Opel GT Forum banner
21 - 31 of 31 Posts

·
Opel Rallier since 1977
Joined
·
2,278 Posts
Yeah, that is what is odd about the 14:1 AFR at WOT. Makes me wonder what the AFM and TPS are giving to the computer at WOT; I looked over the Motronic info I have and it says the the TPS will be at 4.5v or more for WOT, and that will tell the computer to enrich the mixture. I know my Jetronic has a WOT switch that closes in the last 10% of throttle movement and tells the computer "Ignore the AFM...let's GO!" and it really does give the car a kick in the pants with more fuel (and fixes a lean spot a < 90% throttle. (I'll see how much that AFR changes when I get the AFR gauge on that system.) So it might be worth checking the TPS at WOT to make sure it is giving enough voltage to the computer... kinda like the opposite problem with the idle voltage from before as I recall.

But maybe the Motronic design assumes lots of WOT on the Autobahn and wants to not give crappy fuel mileage for long runs? Just a SWAG.....

And good deal on the fuel pressures now, Gordo. What you have now is coherent compared to the documentation.

One of the big benefits of production FI is keeping the AFR leaner overall. That is not just for economy and emissions, but has the side benefit of less the unburned fuel in the cylinders. Many/most don't realize that never is 100% of the fuel burned. Even at 14.7 stoichiometric AFR, there is unburned fuel (as well as unused O2). Less unburned fuel means less fuel residue in the cylinders and seeping down the bores, and results in notably less cylinder bore wear. So that is one reason I'd like to keep my light/medium cruise AFR leaner.... it is a known factor in improving bore life. The difference in the Mopar small block LA engines (carbed) and the Magnum engines (FI) in bore wear rates is mentioned often over on Moparland. Essentially the same guts inside, same 5.2 and 5.9 L displacements, same bore and stroke, etc., etc., more compression and power for the Magunms, but much less internal wear for the FI'd Magnums is consistently the outcome.

What AFR meter do you have, I may ask? I'd like to look at the calibration matter. But if they do not mention it, then there probably is none, and the numbers are all within reason anyway. Of course, the O2 sensor in the car is a narrowband and will have a given accuracy, just like each of the wideband 02 sensors we use. And the computer is going to enrich based on lower coolant temp at some point, but I have not a clue if the 160-180 temp reading is low enough to be a factor. Hey, you're retired.. I am just trying to keep you from getting bored LOL

And I did race and hope to retire soon and do some more before it it too late. But I put a high value on efficiency. Keep that SAFR chart of target AFR's handy for different operating conditions for the next FI incarnation. I would use those numbers for targets rather than what the Motronic is doing now.

All good stuff....
 

·
Just Some Dude in Jersey
Joined
·
15,454 Posts
Discussion Starter · #22 ·
This is it. It's just a dirt cheap meter probably made by a Chinese dude in his kitchen. It's sold under various names. I just needed a reference point, nothing fancy. It has a needle and an LED readout and you can change the colors by pushing the button.

 

·
Super Moderator
Joined
·
13,934 Posts
I want the engine to last forever, I'm not that concerned about fuel economy or emissions or power. Is Opel's selection of 12.5 at idle, 13 at cruise, and around 14 at WOT the best for engine longevity? I don't know. I'm going to presume that they know a lot more about this stuff than I do.
Just an FYI, but the 2.4’s are fairly well known to crack the factory cast iron exhaust manifolds (if you recall, yours was cracked and I repaired it).

This has to do with a combination of German WOT high speed driving habits and the lean AF ratio.

It shouldn’t be an issue for typical US driving conditions however.
 
  • Like
Reactions: The Scifi Guy

·
Registered
Joined
·
1,017 Posts
You are fine as long as you don’t have pinging.
You could spend all day at 6000rpms at 14:1 if your cooling system could keep up and you aren’t pinging. If have a lot of advance, a milled head, etc, go richer to avoid pinging from hot spots, but a stock high comp 2.0L doesn’t give a crap.

I would be willing to bet that over 50% of Opel owners are either running WOT afrs above 14:1 or below 11:1 Because you can’t tell without either an AFR gauge or a stop watch with most engines. And spark plug will still be pretty tan even at those relative extremes.

Now if you are on the race track. really pushing the car I wouldn’t expect the motor to last long anywhere above 14:1 AFR. The EGTs and cylinder temps would be crazy I bet.
I’d have to agree with you on this 14:1 @ WOT. On the 32/36 it has an enrichment system that frequently fails at WOT. A lot of us are driving around using that carburetor baseline jetted.
I’ve blocked that feature off & use a 170 main on the secondary. I’m at 12.8-12.9:1 @ 2,000 ft where I live and 13.4 when I’m at sea level. So perhaps I should be fine since I’m sustaining 6,000 rpms for 5-10 seconds swinging up a ramp to the freeway or whatever, that’s richer than 14:1. I figure trouble would set in if I ran 13.4:1 WOT around the track for 1/2 mile or more though 🙃
 

·
Just Some Dude in Jersey
Joined
·
15,454 Posts
Discussion Starter · #25 ·
Recent experiments and ideas:

So, my stock FI works as advertised: It's reliable, starts predictably, gets good gas mileage, and my AFR gauge says that's what comes out the pipes is in a safe range.

My only regrets or disappointments are that it's much less powerful than my side draft set up and there's hesitation when I come off idle. After setting fuel pressure to close to what a stock Motronic system requires, somewhere between 35-40 psi, and running the tests previously mentioned, I was annoyed by the weak idle. I couldn't even here the engine run when idling or coasting and the car would be a little tempermental maneuvering around at idle, like backing up my driveway and transitioning from idle. Entering traffic from a driveway or such always had the possibility of me stalling or bogging if I gave it too much gas. I had to very gently ease down on the pedal in those situations. Tire spinning? Forget about it, no way can I do that. I spun tires easily with the side draft.

So, Charlie brought up the idea that my fuel pump's no return concept might be at fault or maybe the vacuum compensater function wasn't friendly with my set up. I also entertained the thought that maybe there was a dead spot in my throttle position sensor. Well, this weekend I installed a new TPS and maybe it helped the situation of the hesitation a bit, but probably not. So, then I disconnected the vacuum compensater hose and plugged things off and this seemed to make a big difference. Now, when I'm idling, the compensater hose to the regulator DOESN'T drop the fuel pressure by 7-8 psi. The car seems to idle with much more authority, instead of sounding "weak". After driving to several car shows this weekend I'm happier with that hose disconnected. Still a little hesitation, but much better than before I took that hose off.

I was partially basing my previous tests on how the car performed at idle, as well as the AFR at all ranges. Higher fuel pressure seems to make my car perform better at idle and transitioning to Run. I'm also looking into the possibility of putting one of the Holley Sniper carbs in a sideways configuration on my SSD manifold for either this car or my new gull wing one. One thing I noticed was that all of their Sniper carbs are spec'ing 58psi for fuel pressure. Hmmm......I'm using a different style of fuel pump/regulator than stock and I'm using Mustang injectors that are rated at higher than stock Opel pressures and disconnecting the vacuum compensator and running higher pressure at idle improved things a lot. So, I think I will try doing some more tests at fuel pressures up to 58psi. That's almost double what stock Opel suggests. I did notice during my previous tests that the engine started to sound more ballsy after 40psi. I definitely have more balls and performance at idle now with higher fuel pressure, so why not try really jacking up the pressure and see what happens? My AFR gauge will tell me if I'm going too rich. Stay tuned.....:)
 

·
Senior Contributor
Joined
·
5,067 Posts
What is the CC/Hr or Lb/Hr of your Mustang injectors. They are probably designed to run at 45psi.
 

·
Just Some Dude in Jersey
Joined
·
15,454 Posts
Discussion Starter · #27 ·
I'll have to check with Charlie, but 45psi sounds familiar.

I don't honestly think I could run the engine at 58psi. All I know is that my car had a certain distinctive exhaust sound when I had the SSD. It sounded just like a strong V8. Numerous people at car shows even said this to me. It didn't sound like that since the FI, especially at idle, which is what I was doing at car shows when those people made those comments. Yesterday, at a show, after I had removed the vacuum compensation, someone made that comment again for the first time since the FI swap. I too noticed that it sounded like I remember and the car seems to behave better at idle now under all circumstances.

I'll check with Charlie to find out what the injectors are rated at and use that number as a goal. Maybe that's the deal: You have to set your pressure according to what your injectors are rated at to get proper performance. Maybe using lower pressure than injectors are rated at causes wonky performance.

Tick...tock...tick...Okay, I just talked with Charlie and he said that the injectors are rated about the same as oem Opel injectors at about 40-42psi and he said that 80% of all Bosch injectors run at that. They might have a slightly different spray pattern than oem injectors. But, back he goes to the fuel pump and the nuances of my system's set up and not having the pressure regulator in the middle of the fuel rail, as the fuel rail was designed. He suggests that maybe because of the way the Opel fuel rail was designed and me modding away the regulator on the rail, maybe I'm not getting optimum pressure at the suggested Opel Motronic setting and I need to boost it a bit to compensate.

So, at some point I'll do some more tests up to pressure as high as 45psi and see what kind of results I get.
 

·
Senior Contributor
Joined
·
5,067 Posts
What the injectors need to atomize properly and what the software is designed for may be 2 different things. Also, are the new injectors the same flow rate as the stock injectors? I doubt that you are getting enough pressure drop in the fuel rail to affect the flow rate of the 2 farthest injectors. The sound of your engine with the side drafts on was probably from the intake noise. With the long intake system that you have now that sound will be much less.
 

·
Opel Rallier since 1977
Joined
·
2,278 Posts
You've clearly upped the pressure and modestly enriched the mixture.at idle and light to moderate cruise.

The pressure and flow ratings of injectors are ratings for testing only. The system design pressure spec is the baseline of operation regardless of the published test spec numbers. Any injector can be run at higher or lower pressures within limits to get more or less flow. All OEM systems that I have ever seen run with a vacuum compensation, so the injectors get run at a range of pressures. (My stock Opel replacement injectors are being run at about 7-8 psi higher overall pressures with the vacuum compensation, than in the stock setup, to help compensate for the added airflow of the mild engine mods at wider throttle openings and the way in which the AFM and computer interact at those throttle openings.)

I can't recall how you set up the fuel rail with your remote reservoir. Is there just a supply line to the rail, or both supply and return lines? If there is both, you can test the fuel rail idea. Put 2 fuel pressure gauges that have been calibrated to each other; one in the supply line to the rail and one in the return line and compare the readings. Any drop ought to be the worst at idle, especially with the vacuum compensation connected. And realize that a 1 psi rise or drop at your range of operating pressures means approximately 1.2% change in fuel flow.... not a lot. So it would take a few psi of pressure drop in the rail area to be able to feel it like you have.

One other related thing is that you remote reservoir system is rated at a LOT of flow to be able to support a lot, lot more HP than you have. If you have a both supply and return lines to the rail, then the excess flow used to regulate pressure is very large ofr a lrge flow system, and could cause more drop anywhere in the area of the rail.

BTW, have you looked at the plugs to check for consistency cylinder-to-cylinder?
 

·
Just Some Dude in Jersey
Joined
·
15,454 Posts
Discussion Starter · #30 ·
The pump pumps fuel about 24" to the rail, the rail's return is blocked off. The pump has the regulator built in, so it's 24" away from the rail. No, I haven't checked compression at each cylinder. I'm using the solid aluminum 2.4 Motronic fuel rail, which has an extra chamber at the top where the stock fixed-pressure regulator was, plus the return line exit. The pressure regulator passages and the return have been modded away and/or blocked off. The pressure testing port is in that upper chamber. Earlier, I had seen some major oscillation of the pressure gauge needle at lower pressures, I don't have that oscillation now that I'm at 38-40psi. So, one thought is that the oscillation of my gauge was caused by a sort of cavitation or ricochet effect happening inside the rail. I don't see that extra chamber at the top of other cars' fuel rails.

This pic shows the fuel rail and the mods I did.
429721


429722


I'm not sweating this issue and am looking for an alternative FI system that takes up less space. We're going to try to put one of the Holley Snipers sideways on my angled SSD manifold via an adapter plate. That will likely get put on my new car's 2.4 engine and I'll spend time working out the kinks on that car. If the idea works out better overall than how my Motronic performs, then I'll do the same mod on the GTX's engine. For now I'll do another round of pressure tests. I suspect that I won't be able to increase the pressure much more than where it's presently at, without running too rich. We'll see. :)
 

·
Opel Rallier since 1977
Joined
·
2,278 Posts
That's all you can do... get to the base line of the Motronic as designed and experiment from there. OK on the rail...... so the regulator excess flow does not go through there and would say that pressure drop to this rail is not likely at all particularly at idle; just not much flow to cause it.

I can understand the change. I have taken the Jetronic as far as I care to bother; as I have it now, it is a bit rich at idle and leans out in the 60-90% throttle range, and then is OK at WOT. So I can't simply go richer or leaner without making it worse at one range or another. I could mess with the analog computer and AFM curve but that would become involved. Easier to put the dual DCOE's on LOL

BTW, I was just suggesting looking at the plugs for signs of rich or lean in any particular cylinder. Not any real reason to suspect any, just an easy check. AFR meters can't catch a cylinder that is off.
 
21 - 31 of 31 Posts
Top