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Discussion Starter · #1 · (Edited)
Multiple times I have read the mention of bringing original Opel 70s fuel injection systems into the modern age with programmable digital ECU, modern high pressure fuel system, etc.

I like this idea and want to do it.

Here is an example…
For 1.9-2.0 Engines you can use the 1975 Opel L-Jetronic Intake manifold and injector plates or weld in injector bungs (probably best solution) but you will have to make a fuel rail (the 1.9 L-Jet setup uses ancient injectors with hose barbs and hose connections which can be made to work but I'm not sure it is worth the effort). If it were me I would make a fuel rail and use the stock injector plates (which I have done) which is a good solution but a better solution would be weld-in injector bungs and a custom fuel rail. Not really expensive but does take some work. For the L-Jet intake manifold you will have to use/adapt an aftermarket throttle body because the Opel L-Jet TB does not use a Throttle Position Sensor (potentiometer) but rather a Throttle Position Switch which is not compatible with any modern EFI.
I will mine other examples form the forum and reference them here as I find them.

This thread will capture my project/journey to deliver on this conversion and updating of nearly 4 decades of fuel injection technology. We will keep what works well (physical manifold) and update the rest.

Hopefully the performance improves in many ways as restrictions are eliminated.
 

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Discussion Starter · #6 · (Edited)
1975 Opel Fuel injection is not sequential, it fires all 4 injectors at the same time and inject twice per four stroke cycle.
Hopefully that can be changed with modern fuel injectors and modern ECU brain. I just don’t know enough yet to understand all of the sensor inputs required for sequential electronic fuel injection. Would sequential EFI require a crank sensor and cam sensor?
 

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Discussion Starter · #7 · (Edited)
So one of the principles during the update is to keep this system is SIMPLICITY. I want to keep it as simple, clean, and compact as possible. That means using 1 part where possible instead of 2 of 3. In the words of Einstein the design should be as simple as possible, but no simpler. Thomas Edison called combination of functionalities task unification.

The first area up for debate is the throttle body. I believe RallyBob identified a certain Nissan throttle body with similar diameter and bolt pattern spacing. Sounds simple, but hard to find the right throttle body diameter and bolt pattern spacing. The good news about this option is that it includes a modern Throttle Position Sensor, which is great and addresses our need for Throttle Position Sensing input into our modern EFI ECU computer.

Here is the RallyBob posting on the subject.

One of the problems with trying to get an aftermarket ECU to work with an Opel fuel injection manifold is the lack of a proper TPS (throttle position sensor) on the throttle body.

I found one possible solution quite easy to implement, by adapting a late model throttle body to the Opel intake manifold. The throttle body I've used is from a 1991-1994 Nissan SR20DE engine (found in the Sentra SE-R and the Infiniti G20). The bolt pattern of the throttle body is exactly the same as an Opel's, but the securing hardware is different. Opel uses 6mm studs to hold the TB in place, while the Nissan TB is held down by 8mm socket cap screws. I simply removed the Opel studs with vise-grips, then drilled the holes out a bit and tapped them to 8mm x 1.25 thread. Now the Nissan TB bolts right up with the stock Nissan bolts. Even though the Nissan TB is 60mm vs. 55mm for the standard Opel part, the intake plenum opening is already large enough and no port matching is required.

The only thing left to consider is the throttle linkage attachment, which has a few possibilities.
Ideally, I would like the throttle body to also include the idle air control capabilities. Any ideas on options that meet this criteria?

the last item that comes to mind to ponder is the throttle linkage. Three options come to mind:
  1. Modify original highly unique Opel GT hard linkage throttle
  2. Switch to a throttle cable for the final connection
  3. Drive by wire (electronically controlled throttle body)
 

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Discussion Starter · #9 ·
I hunted around for some throttle bodies to repurpose, starting on the Nissan replacement track.
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This Item says it has a built in throttle position sensor, built in Idle Air Control circuit and built in throttle position actuator (sounds like drive by wire). But it only seems to have 1 plug. So, my hunch is that the 6 pins actually control those different sensors / functions.

More research required…
 

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Discussion Starter · #16 · (Edited)
Ok, so I finally got a good first look at the 75 injection manifold from 1.9 liter Opel today. The bare intake manifold flowed really well on my home made flow bench. In fact it flowed better than any manifold I have tested yet.

I was thinking that I would locate the new modern fuel injectors in the center of each runner. But was surprised with what I saw.

The picture below is looking back up the runner from the head side flange. The hole in the ceiling is where the injector was mounted. The yellow circled area is the protrusion that sticks into the air stream. I spent time last summer machining off similar restrictions when porting my down carburetor manifold last summer.
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And, instead of being centered on the port, the fuel injection slot is off center in the runner. And not just a little bit. The offset of the edge of the injector slot from the wall is 5 mm on the left side and 12 mm on the right side.
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So, does anyone know why the hump in the middle? My hunch is that it is there to add metal to the casting for structural support around the center attachment screw for the injector plates. The picture below shows the 3 injector plate mounting screws and the yellow circle represents the approximate hump location.

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But my plan is to weld in the injector bungs, so the mounting holes are not required. If this is the case, my approach would be to grind off the hump and open up the runner so that it has constant cross sectional area. Then I would place the injectors in the center of the air stream.

Does it make sense to center the injectors or am I missing something?
 

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Discussion Starter · #20 · (Edited)
Ok, so I removed all of the humps near the runner ports with my die grinder, much smoother, consistent cross sectional area now, especially on outside runners.

But, as I am lining up the fuel injector bungs, I am seeing the error of my ways. There is no clear path to machine the angled port to receive the fuel injector bung, since the plenum is in the way.
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So, here are the options that I am considering to proceed:
  1. Machine holes for the injector bungs from opposite direction (from the inside of the head flange). May require some clever fixturing, as I am not sure I could get it in my mini mill at the proper angle / clearance.
  2. Drill and weld the bungs into a piece of aluminum similar to original design but welded (Rallybob did a prototype of this). Then weld or screw the aluminum plate to the runner arms.
  3. Machine slots from top using a small hand tool (like Dremel tool). Maybe hard to do this consistently across runners.
  4. Cut off some of the angle / length of the runners and weld back together (@scifi guy mentioned this idea)
  5. Cast intake manifold of modified design (see other thread for this approach). Same design intent ad option 4, but cast whole new manifold or just new arms. I have a sketch of this in CAD already and will post it
 

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Discussion Starter · #23 ·
I was wondering about these things too….
The bump might be there to add turbulence near the injector to improve air/fuel mixing or to push the airflow towards the offset injector to improve air/fuel mixing.
If this was the case, I am hoping that the modern fuel injectors and higher pump pressure provide better atomization.

The injector offset may be to better aim the spray of fuel in the direction that the air flows through head. The ports in the head aren't a straight shot to the valve/cylinder,
What is interesting is that the humps were in the middle (the divider between runners of each arm) so they are not consistently on one side or the other for a given arm
 

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Discussion Starter · #24 ·
So, here are the options that I am considering to proceed:
  1. Machine hole for injector bungs from opposite direction (from the inside from the head flange).
  2. Drill and weld the bungs into a piece of aluminum similar to original design but welded
  3. Machine slots from top using a small hand tool
  4. Cut off some of the angle / length of the runners and weld back together
  5. Cast plenum of modified design with shorter, less angled arms.
no matter the option, I figure I need to get the injector bungs all machined at the same 30 degree angle from parallel. I checked my metal bandsaw And the limit of cutting is about 52 degrees. So I designed and am 3D printing a jig to get the extra 8 degrees. So 60 degree cut from a right angle should be 30 off of parallel
 

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Discussion Starter · #28 · (Edited)
Keep in mind that the oem FI was solely focussed on economy and low emissions, with very little consideration of power. When I was configuring the 2.4 motronic FI on my 2.4, we tried out an aftermarket throttle body that was the equivalent size to the larger throttle on a 6 cylinder 3.0 liter Opel FI system. The 2.4 computer was too dumb to handle the much larger air flow, but at about mid-throttle it had rev response that was super fast, like you are trying to achieve. With a more adaptable computer, that could deal with the higher air flow, we could have made it work and gotten a faster rev'ing engine.

So, what I'm saying is: Don't get locked into the stock throttle size. I don't know how one calculates the maximum size throttle that an engine can handle, but going big on the throttle is something to consider. I'm sure there are detriments to going too big or too small.
Thank you. Could you perchance measure the diameter of the throttle body that you tried? It might be just what I am looking for, as I am going to put a flexible / programmable stand alone ECU and have started gather parts to upgrade displacement to 2.4 liter stoker.

Here is my take on throttle body sizing, mounting methods, and purchasing options under $100 after much research and pondering.
  1. I like the idea of a higher / non constrictive air flow and thus going with larger diameter throttle body as long as it doesn’t make throttle response wonky.
  2. I believe the original throttle body was 55mm? With a 60mm square bolt pattern
  3. I am targeting a 60 mm to 70 mm diameter throttle body for this build.
  4. I would get the 60mm Nissan/Infiniti throttle body, but alas I cannot find one so have moved on to other options - CANT FIND
  5. I have found a 65 mm billet throttle body that comes with a weld on flange and has the same 60 mm bolt pattern (see pic below). I like this as I could bolt it onto the Opel manifold, and have a spare weld on flange for future custom intake builds.
  6. I found a 70 mm billet throttle body I could make with a weld on plate and a little die grinder work — TOO BIG
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Discussion Starter · #30 · (Edited)
Just an FYI, but a 60 mm TB can easily handle 200 hp.

If you go too big on the TB, you end up with a sort of ‘on-off’ throttle response. It can be annoying on smaller displacements.
Thank you for the driver insight and technical perspective. I am definitely looking for a driving experience that makes me smile (not annoyed). So I’ll rule out the 70 mm.
However do you think that the 65 mm would be too binary (on/off) throttle response on a 2.4 street stroker build? It may not be ideal, but it is compelling to me, because it is: available, has the right bolt pattern, and looks good.
 

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Discussion Starter · #31 · (Edited)
So, here are a few pics of an injector bung machined to the requisite Opel 30 degree angle off of parallel. I 3D printed a holder the diameter of the injector bung with the 30 degree angle and took off 10-15 thousandths per pass in the mini mill with 1/2” end mill to get it down to the proper shape.

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Discussion Starter · #33 · (Edited)
Ok, so I am back from a week long business trip. I am working on fitment of the 75 injected manifold in the GT today.

First thing I did was to remove the hood latch mechanism. I will trim it down and put it back in so that it only latches on the driver side. And I cut off the big hood hooks on the passenger side so that the hood can close.

Second thing was to grind off the back of the manifold where it hit the Opel GT heater box. I believe that perhaps a cold start valve of something of that nature mounted here. It seems that the casting had a hole there and then a machined piece was pressed in that had 3 threaded holes.

here is a picture of the end that interfered.
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then a picture after grinding some aluminum away. I just used a big belt sander with super heavy duty 60 grit sandpaper. Here we have breakthrough.
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I will TIG weld a piece of aluminum over the hole from the sanding.
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And here is a side by side (albeit inverted)
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Below you can see how much material was removed. I wanted clearance and prevent any potential bumping.
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Here I am cleaning up the ears off of the hole with my die grinder (great inexpensive tool for aluminum work)
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I had a left over aluminum slug that I had cut with a hole saw when prototyping another project. It was just the right size, so I tapped it into place. During the process, the larger disc insert ring came out. So I just tapped them both into place.
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If anyone else tries this, I recommend welding the inner disc first (lower amperage, cleaner metal, better angle). Then up the amperage for the outer thicker metal to the manifold casting, which is full of all kinds of contaminants.
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my TIG welding is not very good (just started last summer), but it should work as long ad the penetration is sufficient and I don’t have pinholes from the contaminants. I turned the AC balance up when welding the manifold for more cleaning action. Also I still have my big 1/8 tungsten in the torch from welding my other manifold. Should have taken the time to switch back to 3/32 with a nice sharp tungsten.

It cleaned up pretty nice with the belt sander.

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Discussion Starter · #35 · (Edited)
How is your clearance between the manifold and the cowling?
I think that @krewzer must have modified the manifold for the cowling before sending it to me. Here is a picture of the original
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and here is the picture of the modified manifold. The yellow circled area is the part that slips under the cowling.

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here is the under hood fit. It is tight, but fits.
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Discussion Starter · #36 · (Edited)
Just finished machining all 4 of the injector bungs to the Opel 30 degree slant. The picture below are the bungs sitting on the Opel Injection Manifold runners.
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Here is a picture of the machined fuel injector bungs mocked up with the new fuel rail.
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The next steps are:

1) Drill the fuel rail to receive the fuel injector o-rings

2) Get some injectors or at least mock up some rods shaped like the injectors to use as fixture jig to align the bungs to the fuel rail properly for welding.
 

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Discussion Starter · #37 · (Edited)
Well I though I had landed on the direction of going with Holley Terminator X for my ECU / engine management system. I downloaded the software and really like it. However. I can’t seem to find a version of the kit that would work well for my needs on the Opel. And have called them multiple times in the last few days for help. Sometimes they are helpful, but sometimes not.

Here are my criteria (in no particular order):
  1. Budget - Not much over $1000
  2. Easy to use, intuitive, and stable software
  3. Hand held controller (don’t want to have to have it hooked to laptop to get basic info (air fuel ratio) and sensor info. Plus can make simple tune changes etc
  4. Can data log and hook it to laptop to tune it
  5. Works with modern injectors (was planning USCAR EV6 plug modern LS style injectors)
  6. Works with whatever TPS, IAC etc I go with
  7. Clean looking install under
  8. Capable of controlling timing eventually

Here are my frustrations:
  1. There are Holley Terminator X kits for many different cars, but only 1 universal kit.
  2. The universal kit only comes with old style EV1 connectors (I was planning on EV6 injector connectors)
  3. The injector harness has 8 plugs. Holley said I would have to redo the harness to remove the extra plugs
  4. I found 4 cylinder injector harness when searching on my own that will plug right in (verified by Holley, see pic below), but only has EV1 injector plugs and is an extra $100
  5. Can’t figure out which main harness plugs I will need for timing control (crank and cam sensors) down the road
  6. It is pricey at $1300 and doesn’t even come with the $70 cable to plug it into the laptop

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Discussion Starter · #41 ·
Extra wires and customizing seem to be part of the game when modding an old analog car to FI. My present car has a 1990 Motronic system and I had to eliminate half the wires. There were a lot OBD1 diagnostic wires, plus ones for controlling a modern electronically controlled auto tranny, anti-lock brakes, etc., that all had to go. If I had decided to run my oem system with an aftermarket controller, I would probably have had to cut off many, if not all, the plugs and graft them onto the new system's wiring harness.
Makes sense, I will just go into slice and dice mode as the Holley Terminator seems to be the best option for me after weighing all of the factors.

Consider mounting your ECU and extra wiring in the passenger side footwell, which would require cutting a decent size hole in the firewall on that side. I'm customized and don't have the heater there anymore, so I have plenty of room to mount all that stuff behind the dash.
I like this idea. the passenger side footwell is the future planned home for my Opel GT ECU.

I understand your fascination with the latest, coolest, injectors, but, remember: You're rigging an old, weird, car for FI and you're making your own unproven manifold design that may or may not have the optimum injector positioning and general flow of air. Plus, you're thinking of throwing a turbo into the mix? You've got all sorts of variables going on and almost all of them are unproven. The older, larger, injectors were used for decades and nobody complained, I hardly think that the latest gee-whiz injectors would make any noticable difference. The oem FI had the injectors squirt right at the head ports, your concept has them a few inches farther away, Holley Snipers have them all the way at the beginning of the line before the throttle plates, my system will have them just after the throttle plates, carbs introduce the fuel before the throttle plates and various carbs set ups are near and far from the engine, and they all seem to work just fine.
I acquiesce. After a bunch more research, I agree with you, there is not that much of a difference and I will just go with readily available / compatible injectors. I have not yet acquired the fuel injectors. But that day is coming soon. I will focus more on getting the lbs/hour right and fabricating my fuel rail.

I contacted Holley late last week to ask how to configure the system to run the spark and injection like a 2-barrel Holley Sniper. They said to wait 3-4 days for a response and I'm still waiting.
I downloaded the free Holley Terminator X software, and it is actually quite helpful in figuring out what is configurable. Also, the 4th Holley call I made I talked to someone really helpful. He pointed out that on their web page if you select the picture of the item you want and scroll down to the bottom there is an area called "Tech resouces" that has all kinds of info that was helpful for me designing my system.

Are there knock sensors also?
My research indicates that the main wiring harness that comes with the Holley Terminator X does have a place to plug in knock sensor, but the knock sensor itself doesn't come in the kit.

But figuring all that stuff out is half the fun. 😀
Agree! This is a fun project with much problem solving on the way.
 

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Discussion Starter · #45 · (Edited)
I recommend using the injectors that are populated in the drop down menu or aftermarket injectors where you can get full information on the injector dead times an flow characteristics.
Spot on. Thank you for clarifying. That is exactly what I am doing. What I gave up on was insisting that I had EV6 connector injectors. I did not understand what well characterized injectors were at first. But eventually, I downloaded the Terminator software so that I could see which injectors they have characterized. That is great advice.

Here is an example of what injector characterization looks like in the software pull down menu. it is basically how long it takes for the injector to open (in milliseconds), how long it takes to turn off (as a function of voltage), and flow rate at a given pressure. I love the thought of not having to do this myself!
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Roughly 0.5 lbs per hp...
Using this rule of thumb, for a car in the 160-200 hp range / 4 cylinders, would yield roughly 40-50 hp per cylinder * 0.5 lbs/hp = 20-25 lb / hr injectors. This seems to be on the low end of what is offered and you really don't want to go much beyond the 85% duty cycle (too small), or go too big (poor atomization). I will probably select some injectors in the 24-30 lb / hr range, although there are limited size / flow-rate options.
Do they only recommend the latest, coolest, injectors? Or do they suggest any injector within a certain flow rate and other factors?
Here are the injectors listed in the pull down menu from the software. There are a mix of injectors from a variety of manufacturers, with a variety of lb/hr ratings and connectors. Many are OEM injectors through the various years and some are new high performance, non OEM options. Of course Holley would like you to use their injectors. The 2300 Sniper which some have installed on their Opels have 2 x 100 lb injectors.

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Any suggestions from amongst the list? In terms of best bang for the buck?
 

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Discussion Starter · #46 · (Edited)
So progress of the day. My 1994 Nissan Altima throttle body arrived today. It is 60 mm diameter and 60 mm bolt pattern, which matches the 1975 Opel fuel injection intake manifold, and of course has the built in throttle position sensor. It was a filthy mess (being 28 years old), but should do the trick. I don’t know how you guys figure this stuff out, but I am going with the tried and true.

I had a hard time finding the mid 90s 2.0 Nissan Sentra or Infiniti G20 intake manifolds, but the Nissan Altima one seemed much more prevalent. Thank you to those on the forum that shared their experiences and pointed me in this direction..
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I cleaned up the manifold and cut off the hot water line fittings with metal band saw.
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I drilled out the 4 bolt holes on the Opel intake manifold with 17/64 inch drill bit and tapped then with 8 mm x 1.25 mm thread tap. I also ordered M8 x 35mm button head stainless steel bolts to secure the throttle body to the manifold.
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Discussion Starter · #48 ·
Back to fuel injector selection.... I typed the list of the characterized GM injectors from the Holley Terminator software as mentioned above into an Excel spreadsheet. Then, for each option, I did the folowing:
  1. Entered the injector lbs/hr from the software
  2. Calculated the horse power supported (lbs/hr/ injector * 4 injectors * 2 hp / lb fuel * 85% duty cycle)
  3. Figured out the connector type by looking at pictures via google

All of the sudden, the big overwhelming list of injectors that I could not navigate got very small. Most of the injectors either flowed too much or had the wrong connector. The 4th and 5th ones down are my target. That is a relief, because they are modern, relatively cheap, available, use the EV6 USCAR connector, are designed to run at 60 PSI and have 2 holes (better atomization), and have the right O-ring size for the injector bungs I am preparing to TIG weld to the Opel manifold.
Terminator Software InjectorConnectorLbs/hrSupports HPComment
GM 12576341 LS3EV6 USCAR
42​
286too big
GM 12680426 5.3EV6 USCAR
37​
252too big
GM 12594512EV6 USCAR
37​
252too big
GM 12580681EV6 USCAR
29
197choose this
GM 12587269EV6 USCAR
33
224ok
GM 12609749EV6 USCAR
48​
326too big
GM 12613411EV6 USCAR
36​
245too big
GM 12613412EV6 USCAR
50​
340too big
GM 17113553Mini-Delphi
24​
163wrong plug
GM 17113698Mini-Delphi
24​
163wrong plug
GM 25317628
Mini-Delphi​
24​
163wrong plug
GM 25320288
Mini-Delphi​
24​
163wrong plug
GM 25323974Mini-Delphi
24​
163wrong plug
GM 25323974Mini-Delphi
33​
224wrong plug

This decision then frees me up to work on procuring my ECU. I will likely go after an LS kit since it comes with the LS engine harness with the proper EV6 injector harness. Athough I will need to remove 4 of the injector plugs, I think this is a better fit for me than the universal harness with the EV1 injector harness. Of course I could always custom wire it, but as long as I am paying for it, might as well get it right, minimize rework, and maximize reliability.

Any idea on whether the General Motors LS harness will send me in the right direction in terms of connectors for 1) Throttle Position Sensor, 2) Coolant Temperature Sensor, and 3) Crank Position Sensor?
 
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