75 Manta efi

[Gordy]

Trying to re-install the factory efi back on my 1975 Manta (it had a carb on it when I got it). Have replaced with new, the fuel pressure regulator, the thermo time switch, and the temp sensor. Had it running decent once it warmed up (needs a new cold start injector- that has tested bad). Problem is now that when I crank it the plugs immediately foul with gasoline and it will not start. I'll remove the plugs and clean them and re-instll them and when you first hit the key it sounds like it wants to start and then the plugs get soaked again. Bad injectors?? they are all equally soaked when they are removed.

[BQS4]

Gordy;
You may have the same problem I did, I replaced the exhaust manifold on my 75 Wagon and of course, the F.I. plenum has to come off. When I put it all back together, it wouldn't start. After getting a GM master mechanic (right John) it turned out to be the sensor on the thermostat that was not fully seated and this was telling the ECU the wrong situation and basically it was "flooding", or in the F.I. case, too much fuel was being injected. We relieved the pressure (no jokes) and it started right up

[Gordy]

The sensor you are referring to is the air flow valve sensor? That's the one that has the 2 bolts that hold the valve to the top of the thermostat housing.

[BQS4]

Gordy see the attached picture

[Gordy]

thanks for the imput. Actually I replaced that temp. sending sensor with a new one. My problem was the auxiliary valve just on topof that with the 2 large vacuum hoses attached to it. I've got that set properly now so it is open when the engine is cold as the fsm states. The car idles real nice now. Problem I need to troubleshoot now is when you step on the accelerator it stumbles and floods out even though it sat and idled nicely for 5 minutes.

[Gordy]

Still have some problems but here's where I'm at. EFI at this point has new pressure regulator, new thermo-time switch, new temp sensor, and just added a new cold start injector. Auxiliary air valve seems to be set correctly where it is open when cold and closes as it warms (thus fast idle seems to work). Now the car starts immediately when the key is turned and sounds good and idles smoothly. When cold you can give it some throttle and it will rev and not sound too bad. As it warms up, any throttle you give it has it immediately beginning to bog (and spark plugs foul and are dripping with gas) and if you don't let up it will die out at half throttle. Air cleaner is new and the timing is dead on.
Not sure where to go next with this.

[Rionart]

Gordy,
It sounds almost like the distributor is not advancing....

[Aardvaark]

Gordy, are you following the 1975 FSM supplement step by step FI and EGR trouble shooting sections?
The air flow meter may be sticking and needs to be cleaned. When the throttle position switch goes to rich, and the AFM sticks perhaps your going to rich in mixture and fouling the spark plugs.

[markandson]

Almost sounds like your AFM is flying wide open when you ask for some air flow. This situation would make the computer think you are at WOT and would tell the injectors to dump fuel like crazy. I don't know the 75 system at all but I would check this out, there must be some kind of light spring or counter weight of some kind to resist air flow and also return the AFM to closed position when you go back to idle.

[Gordy]

Thanks for the tips. Seems to point towards the air flow meter. Will check it out this weekend. Thanks Guys!

[Aardvaark]

Gordy. FYI, if you don't already know, the plastic top cover on the flow meter can be pried off carefully since it's only held on with silicon sealer.
Once off, you can carefully check the operation of the potentiometer arm as it wipes across the printed circuit board resistor and the spring tension
that holds it back against the air flap in the air duct. You can clean the printed circuit carefully with a small amount of spray contact cleaner.
Reseal the cover with clear silicon after you clean out the old sealer in the seal groove.
Don't be tempted to adjust the spring tension to increase or decrease the rate the wiper are advances as that will make the engine run too lean or rich as that will effect the voltage signal the ECM senses. Also don't try to retension the wiper arm as that will just cause more wear on the circuit board.

Of coarse you should check the air flapper for free movement and cleanliness
of the air flow path.

[dallasmanta]

IF you have checked to see that your injectors are flowing properly, the cold start injectors is not leaking into the intake and all sensors are working properly.
The pressure regulator is checked by removing the vacuum connection at idle and shows a variation of engine speed.

Then the only other component that can impact how much fuel is injected is controlled by the throttle switch has only 3 positions: idle, mid load and full load (to be exact, a bit earlier than wide open throttle) . The idle contact is used by the ECU to recognize the idle condition, and for the fuel cut off (no injectors opening) on deceleration until the engine reaches something like 1200-1400 RPM. Below this RPM range, the ECU starts driving the injectors again. The full load contact informs the ECU that a richer air/fuel mixture is needed (I.e. more fuel), thus the ECU increases the injector opening time by about 9-12% above the time indicated by the airflow meter reading. You can pry off the cap on the throttle plate switch and look to see if the three contacts are set to open and based on the groove track that rotates as the throttle plate is opened. At idle the first set of contacts closest to the throttle shaft will be touching. As the plate is opened the middle contact is moved by the groove to a mid position not touching any other contact till the track moves to the next stage full throttle where the middle contact will touch the third contact.

This should help set this setting.

Ps. Also you can use a vicegrip to pinch off the cold start injector hose to check it per the FSM in the event it is leaking. Hope this helps

[Gordy]

Very helpful info! I did install a new cold start injector last weekend so that is known to be good. Will check out the mass air sensor and the throttle body this weekend. Thanks for all the great info!

[75 wagon]

E-Bay might still have rebuilt flow meters for $125 delivered. Saw one yesterday. Might solve the issue.
I bought one as a spare. Seemed like a good price.

Originally Posted by Gordy Very helpful info! I did install a new cold start injector last weekend so that is known to be good. Will check out the mass air sensor and the throttle body this weekend. Thanks for all the great info!