When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
It is in the scematics. Shorting A to E should start the fuel pump.
E is orange from battery.
A is red to fuel pump.
D is another red to the ALDL connector pin G
Super, thank you. 🙂
With this information we should be able to solve it.
I'm not sure when i/we will be able to check it. But I will update the thread.
Do you mean that the faulty valve prevent the priming?
Cheers/Stefan
I don't know, but it has happened to me.
Just try this: When you first attempt to start the car turn the ignition on.........then back off.......then on.........off.........on....START.
If it then starts..............it is the check valve.
Just try this: When you first attempt to start the car turn the ignition on.........then back off.......then on.........off.........on....START.
If it then starts..............it is the check valve.
It starts with the same cranking needed.
I haven't checked the valve closer, but will do when we will work on it.
Just try this: When you first attempt to start the car turn the ignition on.........then back off.......then on.........off.........on....START.
If it then starts..............it is the check valve.
Why? The system does NOT prime every time you turn your key on. It waits for a while. Forgot how long.
Better test might be to have someone do it for you while you crimp off the feed line after the prime and see what happens.
It is in the scematics. Shorting A to E should start the fuel pump.
A is red to fuel pump.
B is Black-white ground
C is green white from ECM
D is another red to the ALDL connector pin G
E is orange from battery.
Shosting A to E does not start the pump. And 12volt to pin G at the ALDL does not start it either...
I hope my mate will solve it.
( not to easy though... 😂
I have replaced the relay, and no difference.
Previous owner have messed with the pins/wires.
it might have been when installing an alarm.
I does not work, so I have a plan to remove it.
But so far, a plan only... 😂
Originally Posted by aklim
Why? The system does NOT prime every time you turn your key on. It waits for a while. Forgot how long.
Better test might be to have someone do it for you while you crimp off the feed line after the prime and see what happens.
Yeah, the testing is easier being two.
With the tips from you all I'm confident we will solve it. Many thanks to you guys!
It's great with active members. 👍👍
As mentioned in one of the posts it most likely is the cold start relay. I did not read all the posts but check for fuel pressure at the rail during cranking, if you have fuel pressure you can (most likely) rule out all other items other than cold start relay and engine temperature sensor.
Report back on fuel pressure during cranking and then we move on.
Last edited by bjankuski; Jan 14, 2021 at 02:25 PM.
As mentioned in one of the posts it most likely is the cold start relay. I did not read all the posts but check for fuel pressure at the rail during cranking, if you have fuel pressure you can (most likely) rule out all other items other than cold start relay and engine temperature sensor.
Report back on fuel pressure during cranking and then we move on.
I tried to update the thread on my mobile, of course it didn´t work.... So new try...
At last, I managed to measure the pressure.
When I crank I have no pressure util the ECM starts running the Fuel Pump.
When I turn the engine off, first the pressure increases, then after a few seconds it goes down.
When I crank again the engine starts like it should. Even though I can´t see any pressure at once.
I will try to upload two clips, the first clip is my first start, with the long crank.
The second clip is a few seconds later, normal crank. (the shorter file if the order will be wrong)
First time you turn your key to the "RUN" position, the fuel pressure should spike up. If not, it might not be priming. Continue to turn the key off and back to the "RUN" position won't cause it to prime.
If it bleeds off quickly after that, you may have a leak somewhere
Either regulator or injectors or maybe the pump.
Pressure could rise when you turn engine off because manifold pressure goes up. At about the same time he fuel pump shuts off so it depends if manifold pressure rises before pump shuts off.
Pressure could rise when you turn engine off because manifold pressure goes up. At about the same time he fuel pump shuts off so it depends if manifold pressure rises before pump shuts off.
That hasn't happened to me yet and I checked it many times. Not saying it can't.
OK, finally checked in an old '85 Vette FSM. '85 Vette FSM Fuel Control & Fuel Delivery
-when you turn the key to On, the ECM powers the FP through the FP relay for ~2sec.
-as the engine cranks & runs power comes through the Oil Pressure Switch...only...
OK, finally checked in an old '85 Vette FSM. '85 Vette FSM Fuel Control & Fuel Delivery
-when you turn the key to On, the ECM powers the FP through the FP relay for ~2sec.
-as the engine cranks & runs power comes through the Oil Pressure Switch...only...
Hope this helps.
It's kinda blury but referencing stuff on Google images, it doesn't seem like that. It seems like the oil pressure is a backup after it gets running and not the one and only,.
-when you turn the key to On, the ECM powers the FP through the FP relay for ~2sec.
-as the engine cranks & runs power comes through the Oil Pressure Switch...only...
Hope this helps.
Not possible to read, but shoudl be Oil pressure switch AND FP Relay.
Have you measured that you get the initial 2 second pulse?
Not possible to read, but shoudl be Oil pressure switch AND FP Relay.
Have you measured that you get the initial 2 second pulse?
You are correct - it is both. People will never stop posting this BS that the oil pressure switch is the lone pump feed or that it is a "safety cutout".
I haven't been able to measure the 2 sec pulse.
Do you know which pin should have the pulse?
What gives the 2 secs? Not the relay itself I guess?
As a 'quick and dirty ' solution, I guess I could have a manual prime on a separate button.
is there a risk to toast the ECM you think?
I want to fix it correctly of course, but as a temporary solution....
You can manually prime by applying 12V to pin G on the ALDL connector. See schematics posted.
That can not toast the ECM because pin G is disconnected when the ECM engages the FP relay.
The 2 sec pulse is on from the ECM to FP relay. You can measure if you remove the FP relay. See schematics.
You can manually prime by applying 12V to pin G on the ALDL connector. See schematics posted.
That can not toast the ECM because pin G is disconnected when the ECM engages the FP relay.
That's also why I suspect the FPR is connected wrong... applying 12V to pin G, I the pump is not working. 🙄
I applied 12v to the pump connector direct, then it works...
In a couple of weeks I will get help from a fellow C4 owner. I blame him for my purchase, so he is helpful. Haha...
