Stock EFI fuel control problem

[anastosmotors]

Hello,
Need help,
Vehicle is a 72 Ascona 1.9L using stock EFI from a 1975.
Unable to adjust fuel mixture i.e. sometimes rich sometimes lean.
When vehicle electrical system is loaded fuel mixture always leans out, usually enough to stall engine .
Checked grounds ok .02v drop loaded.
Charging voltage 13.8v wihout load, never dropped below 13v loaded.
Have tried to adjust the mixture at the airflow sensor and it does respond to adjustment but does not stay consistant when rpm's increased and then return to idle.
Airflow sensor resistance measurements within specifications and voltage changes at sensor seem smooth while engine is running.
Tried a different computer and had same results.
Anybody seen this before?
Any thoughts or suggestions?

[hrcollinsjr]

Originally Posted by anastosmotors Hello, Need help, Vehicle is a 72 Ascona 1.9L using stock EFI from a 1975. Unable to adjust fuel mixture i.e. sometimes rich sometimes lean. Tried a different computer and had same results. Anybody seen this before? Any thaughts or suggestions?

Pete,
I am NOT an EFI guy but a question to maybe assist others in helping you. You said stock '75 EFI. Is the engine stock? I was under the impression that a stock '75 EFI could only handle a few modifications.

Harold

[dallasmanta]

Pete two places to look first. Run a fuel pressure test to see if you have the right pressure drop for a loaded engine condition. Then check the temp sensor this unit is the only item on the Opel EFI that controls the fuel mixture simulating a cold engine more fuel vs a hot engine less fuel by controlling the duration of the injectors staying open.

If this all checks out check the fuel injectors to make sure they have even flow and a good spray pattern..

Hope this helps Ron

[Aardvaark]

Pete.
Also check for a vacuum leak downstream of the air flow meter.
It sounds like you have an unauthorized source of air the air flow
meter adjustment can't make up for.
Check everything from the master cylinder diaphram to the intake manifold
at the head flanges. Been there and done that on my stock 1975 Ascona and other EFI cars like Saabs and VW's.

[dallasmanta]

Excellent suggestions.. an old trick to find vacuum leaks on the EFI is to spray carb cleaner along the various hoses as suggested and listen for a change in engine speed will help you find the breach faster. Ron

[ghcoe]

This is in the bosch manual. Not sure how it senses voltage. Maybe you have a wire that is giving faulty info to the brain since you notice the problem with electrical loads.

[tekenaar]

Originally Posted by anastosmotors Hello, Need help, Vehicle is a 72 Ascona 1.9L using stock EFI from a 1975. Unable to adjust fuel mixture i.e. sometimes rich sometimes lean. When vehicle electrical system is loaded fuel mixture always leans out, usually enough to stall engine . Checked grounds ok .02v drop loaded. Charging voltage 13.8v wihout load, never dropped below 13v loaded. Have tried to adjust the mixture at the airflow sensor and it does respond to adjustment but does not stay consistant when rpm's increased and then return to idle. Airflow sensor resistance measurements within specifications and voltage changes at sensor seem smooth while engine is running. Tried a different computer and had same results. Anybody seen this before? Any thaughts or suggestions?

. . . check the fuel FLOW from tank to fuel pump! . . . on the '75 tank, it's a 1/2" line between the tank and the fuel pump and, even then, if the in-tank fuel sock clogs up from rust particles restricting free fuel flow (35 year old tank!), you'll get exactly your symptoms as pump needs unrestricted flow at inlet to maintain pressure under all engine loads.

That said, it is also critical that you do not restrict RETURN fuel flow by making the return line too small, as it will then act as a pressure regulator by restricting regulator bypass fuel flow making the mixture too rich. Adequate unrestricted fuel flow tends to be much more critical in FI systems as they continually recirculate excess fuel not required by the engine back to the tank.

All this learned from personal school of hard knocks . . . finally had to remove the fuel tank on my '75 Ascona to get it cleaned and sealed because of continuing problems with internal rust particles clogging up the fuel strainer inside the tank. I authored a thread with many pics about FI fuel sender/strainer/tank problems about a year ago . . . go look there, Pete . . .

[anastosmotors]

Hi everyone
Thanks for your replies.

We found the supply voltage to the ignition system was the root cause of our problem.
Key on engine off the voltage was 12V, but when runnuing would drop to approx. 8V.
After consulting the wiring diagram found that there is a resistance wire in the power supply to the ignition coil.
This would be fine with the original ignition but this car has Compufire D.I.S. ignition system.
As a test we jumpered a 12V feed to the ignition module and the car ran much better with no problems handling all electrical loads in gear.

Question..... Does anyone know where in the vehicle the resistance wire is located?

Would it be a simple thing to replace or do you think it would be better to by-pass it with a new power feed to the ignition module?

[wrench459]

Originally Posted by anastosmotors Would it be a simple thing to replace or do you think it would be better to by-pass it with a new power feed to the ignition module?

Why not use the clear wire to control a relay to power up the module?

[RallyBob]

Originally Posted by anastosmotors Question..... Does anyone know where in the vehicle the resistance wire is located? Would it be a simple thing to replace or do you think it would be better to by-pass it with a new power feed to the ignition module?

I just replaced the resistor wire in a '71 Ascona harness a few weeks ago. It runs directly into the fuse box, but there's quite a lot of extra wire taped up to the main harness, as the length of the resistor wire affects the resistance. Not wanting to cut the harness apart, I soldered a new 18 gauge wire to the resistor wire, and pulled the new wire right through the harness cover. Soldered it to the same terminal on the fuse block the resistor wire was attached to, and it almost looks OEM now.

[wrench459]

Originally Posted by RallyBob I just replaced the resistor wire in a '71 Ascona harness a few weeks ago. It runs directly into the fuse box, but there's quite a lot of extra wire taped up to the main harness, as the length of the resistor wire affects the resistance. Not wanting to cut the harness apart, I soldered a new 18 gauge wire to the resistor wire, and pulled the new wire right through the harness cover. Soldered it to the same terminal on the fuse block the resistor wire was attached to, and it almost looks OEM now.

me would think

that the load would be less on the switch using a relay

the relay field only takes 100ma or so