Ideas for a stubborn fuelie?

[Gary Sullivan]

I am having some issues getting a 75 with FI to run right and thought maybe some of you have had similar experience. It's symptoms are these: On startup, it runs just great. Starts right up. Runs smooth and decent power. Two or three minutes after it has been running, it seems to gasp and starve and then I have to pump it and floor it to get enough power and make it home.
I have been running through the various checks for many many hours now. I have already freshened up the ignition: fresh point, plugs, wires, rotor, changed out a failing coil and condensor, reset & checked dwell and then timing, set the valve clearance, did vacuum checks and fixed a slew of leaks. It has good fuel pressure, good vacuum now, and the dual relay checks out.
Perhaps the solution is to test each and every piece of all the systems, but that is really gobbling up the time.
75's sometimes have problems with those fuel pumps so after I get it running I'm inclined to go ahead and permanently install a fuel pressure gauge and a fuel pump indicator light.
Anyone had similar experience with a fuelie? I was hoping to not have to go through the entire manual to get it to run okay.
Appreciate any insight/ideas.

[BQS4]

Gary;
I too have a 75 Opel, and right now, it's running great, but, I have been told that the injector design is not the greatest. Even though mine is daily driven, the tips of the injectors will rust and cleaning them will not help. A reliable source has told me that VW type 3 injectors will replace the Opel ones and are of a far better design. I don't know if this may be your problem, but, you might want to look into it and let us know.

[Paul]

How new is the fuel filter?

[Gary Sullivan]

I just bought the car a short time back. Looks to be a new filter on it. I also tested the EGR and it checks out.
I thought I would look at the air flow meter next (but my good past history with 75 fuelies suggests that few fuel inj. components fail in my experience.)
The fact that the problem seems to occur during or at the end of warmup makes me suspect some of that circuitry in the brain box/control unit.

[David McCollam]

There are a couple of things I would suggest on the static test of your FI system. Have you taken the engine past idle for the test to observe the fuel pressure under difference RPM's. This will let you know if the pressure regulator is working correctly. If the pressure drops significantly under acceleration (below 25psi or so) you may have a problem.

Second, can you connect your pressure gauge and observe the car under load while driving. You could have a resistance problem in the FI control as you said. Also, you could have a fuel starvation problem from a clogged main filter or a sediment covered pickup screen in the tank. I would replace the main FI filter and pull the fuel sender to check the pickup screen.

[Gary]

It sounds like it runs well when the cold start injector is on but leans out when it warms up. Vacuum leak? Did you spray carb cleaner around all vacuum connected hoses and other areas?

One problem I had with my '75 was a vacuum leak at the throttle plate due to the bushing wearing.

[wrench459]

Even if the fuel pressure is right you might have a fuel volume problem.
Rule of thumb is a pint in 15 seconds.

[Gary Sullivan]

Thanks. Those seem to be some good ideas. I didn't closely check the throttle plate for leakage but had used the throttle spray technique on the hoses, and additionally made a tester to lightly pressurize the manifold and did a control leak down test as well and found a boatload of hose cracks. I've now got it up to 18 lbs vacuum at idle now (I did have 14). I think I'll just swap out that filter and look for the tank screen and watch that fuel pressure on road conditions. I'm also going to take a close look at the pump wiring. The car has a little more road grime and grit on it than some cars and I had previous experience with wiring corrosion issues with the fuel pump on other 1900's.
Appreciate the help guys.

[tekenaar]

There are a couple of things I would suggest on the static test of your FI system. Have you taken the engine past idle for the test to observe the fuel pressure under difference RPM's. This will let you know if the pressure regulator is working correctly. If the pressure drops significantly under acceleration (below 25psi or so) you may have a problem.

Second, can you connect your pressure gauge and observe the car under load while driving. You could have a resistance problem in the FI control as you said. Also, you could have a fuel starvation problem from a clogged main filter or a sediment covered pickup screen in the tank. I would replace the main FI filter and pull the fuel sender to check the pickup screen.

The pickup screen is extremely fine mesh which, even if you can get it clean in the first place, will soon clog up again to cause fuel starvation . . . AGAIN! . . . ask me how I know!!

Drain gas tank (remove bottom screw (of 5) from fuel tank pickup/sender and remove it from the tank. Discard the fuel pickup screen and replace with external fuel filter between the tank and FI-pump. I'm in the process of modifying my pickup with an external ball valve so I can shut off fuel flow when replacing the external pre-filter.

[Gary Sullivan]

I finally got a bay open in my shop so I could pull the fuel sender on my 75. Came out easily, but no cylindical screen came out with it. The unit goes in and out just fine, but no mesh cylinder??? I guess it's possible there is one hiding in behind that partition in the well in the middle of the tank. Maybe this means dropping the tank so I can turn it upside down and bang on it or fish one out, but I kind of hate to do that without knowing for certain there is actually one in there. Anyone had this happen? Have any clever ways of scoping out whether or not a screen is lurking in the tank and how you get the stinker out?

[tekenaar]

The pickup screen is extremely fine mesh which, even if you can get it clean in the first place, will soon clog up again to cause fuel starvation . . . AGAIN! . . . ask me how I know!!

Drain gas tank (remove bottom screw (of 5) from fuel tank pickup/sender and remove it from the tank. Discard the fuel pickup screen and replace with external fuel filter between the tank and FI-pump. I'm in the process of modifying my pickup with an external ball valve so I can shut off fuel flow when replacing the external pre-filter.

I finally got a bay open in my shop so I could pull the fuel sender on my 75. Came out easily, but no cylindical screen came out with it. The unit goes in and out just fine, but no mesh cylinder??? I guess it's possible there is one hiding in behind that partition in the well in the middle of the tank. Maybe this means dropping the tank so I can turn it upside down and bang on it or fish one out, but I kind of hate to do that without knowing for certain there is actually one in there. Anyone had this happen? Have any clever ways of scoping out whether or not a screen is lurking in the tank and how you get the stinker out?

. . . exact same thing happened to me when I drained my tank just prior to chemical cleaning and sealing, which is what I finally ended up doing on mine. I messed around with numerous approaches to using an external pre-filter/screen and shut-off valve, all of which had drawbacks with which I was not happy.

Dropped tank and "shook it" to get that screen out, as you said, before I sent it for clean-and-seal. That screen has plastic/nylon ends on it and when there's a bit of corrosion on the external surface of the pickup tube's end around which it is mounted, there isn't sufficient friction left to retain it when you remove sender/pickup from the tank. It's there though, trust me.

[tekenaar]

. . . exact same thing happened to me when I drained my tank just prior to chemical cleaning and sealing, which is what I finally ended up doing on mine. I messed around with numerous approaches to using an external pre-filter/screen and shut-off valve, all of which had drawbacks with which I was not happy.

Dropped tank and "shook it" to get that screen out, as you said, before I sent it for clean-and-seal. That screen has plastic/nylon ends on it and when there's a bit of corrosion on the external surface of the pickup tube's end around which it is mounted, there isn't sufficient friction left to retain it when you remove sender/pickup from the tank. It's there though, trust me.

Forgot to say what I did about my loose fuel pickup screen . . .

Thoroughly remove all corrosion from the vertical pickup pipe to which the cylindrical screen mounts.

When you try to mount that screen, it will be even more loose on the pickup pipe due to your diligent corrosion removal.

I then cut an ~1" length of 1/2" shrink tubing, slid it over the pickup tube to where the pickup screen ends up when mounted and heat-shrunk it to the tube there.

When cool, oil both heat-shrink tube area and the ID of the screen mounting hole and slide it up the tube and over the heat-shrink, turning the screen as you go.

That's it!

[Gary Sullivan]

Thanks. It's particularly helpful to hear from someone who has "been there, done that".
I still haven't pulled the tank yet. I am pondering that, while still relishing the experience of the waves of gas fumes cascading into your face working down there. Yeesh.
Yesterday I was looking to fab something to fish the piece out. It is probably nuts, but I am tinkering with adapting a 1/8" spring loaded toggle wall anchor to slip through the feed tube or find another way to "spear" the rascal through the feedtube. Maybe someone else has better trick. If something like that doesn't work I will still end up pulling the tank anyway.
On a similar, but related note, re: your bad experience with an external ball valve shutoff and pre-pump filter. I had planned on going that route, but it is pretty complex messy plumbing and doing a new filter back in the tank does make more sense.

[tekenaar]

Thanks. It's particularly helpful to hear from someone who has "been there, done that".
I still haven't pulled the tank yet. I am pondering that, while still relishing the experience of the waves of gas fumes cascading into your face working down there. Yeesh.
Yesterday I was looking to fab something to fish the piece out. It is probably nuts, but I am tinkering with adapting a 1/8" spring loaded toggle wall anchor to slip through the feed tube or find another way to "spear" the rascal through the feedtube. Maybe someone else has better trick. If something like that doesn't work I will still end up pulling the tank anyway.
On a similar, but related note, re: your bad experience with an external ball valve shutoff and pre-pump filter. I had planned on going that route, but it is pretty complex messy plumbing and doing a new filter back in the tank does make more sense.

First, you won't be able to "fish out" the screen no matter what . . . trust me!

Second, remove lowest pickup mounting bolt to drain tank . . . slow, but least mess!

Third, forgot to say, but clean screen by blowing compressed air from inside to outside of mesh screen, i.e. opposite normal gas flow!

[Gary Sullivan]

Thanks again. Your sharing your experience probably saved me some unnecessary aggravation. I did pull my fuel tank and the little fuel filter practically jumped into my hand. This one is collapsed inward on four sides all the way to the inner core so I am not certain I should try to reuse it. Fuel pump has a lot of oomph to do this much damage.
You mentioned trying an external pre-pump filter and shut off valve, but you weren't satisfied with it. That could easily be messy plumbing, but are there some other issues that would make that arrangement not work well?

[tekenaar]

Thanks again. Your sharing your experience probably saved me some unnecessary aggravation. I did pull my fuel tank and the little fuel filter practically jumped into my hand. This one is collapsed inward on four sides all the way to the inner core so I am not certain I should try to reuse it. Fuel pump has a lot of oomph to do this much damage.
You mentioned trying an external pre-pump filter and shut off valve, but you weren't satisfied with it. That could easily be messy plumbing, but are there some other issues that would make that arrangement not work well?

. . . mostly space/fitment problems for the 1/2" tubing/hose size required between tank and pump . . . very little room and orientation of tank outlet in relation to pump axis - 135° - makes this near impossible without moving EVERYTHING around! Even then, the results would be less than satisfactory, IMO . . . too kludgy looking!

Function is always my first fabrication priority . . . followed very closely by appearance! This met neither criteria . . .