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Hej,
I'm new to this forum and also as a C4 owner. And excuse my Swenglish, I'm from Sweden so if i write funny, thats why... 🙂
I've bought an 85 C4 and i have an issue with long crank time until the engine starts. When it run there are no problems. Just the crank.
I replaced the fuel pump relay with no improvement.
When I Turn the ignition on, should I be able to hear the pump prime?
What is managing the 2 second priming?
If i understand correct, the ECM take charge when the oil pressure is above some value?
If it is a pump problem I guess I would have problems all the time. The engine runs great, when it's started. No lack of performance.
Are anyone able to explain the prime way of working?
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
Originally Posted by Sac_197
Hej,
I'm new to this forum and also as a C4 owner. And excuse my Swenglish, I'm from Sweden so if i write funny, thats why... 🙂
I've bought an 85 C4 and i have an issue with long crank time until the engine starts. When it run there are no problems. Just the crank.
I replaced the fuel pump relay with no improvement.
When I Turn the ignition on, should I be able to hear the pump prime?
What is managing the 2 second priming?
If i understand correct, the ECM take charge when the oil pressure is above some value?
If it is a pump problem I guess I would have problems all the time. The engine runs great, when it's started. No lack of performance.
Are anyone able to explain the prime way of working?
Thanks for your reply. 👍
Do you think so?
The engine runs with no issues when it finally starts.
Do you hear your pump priming?
I will try to check the injectors . 🙂
If you have access to a fuel pressure gauge attach it to the Schrader valve and view pressure after you turn the pump On and after the engine finally starts.
After it starts, tap the accelerator while watching fuel pressure; if pressure drops replace the fuel filter under the passenger side along the rail.
Check spark plugs for condition and gap.
Does it idle smoothly and smooth under light acceleration??
When I Turn the ignition on, should I be able to hear the pump prime?
What is managing the 2 second priming?
If i understand correct, the ECM take charge when the oil pressure is above some value?
If it is a pump problem I guess I would have problems all the time. The engine runs great, when it's started. No lack of performance.
Are anyone able to explain the prime way of working?
Sure but so what if you do hear it or not? I don't know what the pressure is which is important. I need to know if it builds up pressure quick and whether it holds pressure or not. For that you need a fuel pressure gauge not your ear.
ECM does a 2 second prime.
The common thought is that the oil pressure is a "protection" circuit that only gives fuel pump current when it hits a certain oil pressure. Unfortunately, if you look at the diagram, at least in 91, that is not true. It is a backup circuit.
If you can actually check the power with a dyno that isn't your butt, it would be more revealing. I would see if the pump can keep up to demand with a fuel pressure gauge taped to the windshield when you do a wide open throttle run.
When you turn the key on, it primes for 2 seconds. When you turn it off and then on again, it DOES NOT. Some time has to elapse since the first key turn for it to prime again.
If you have access to a fuel pressure gauge attach it to the Schrader valve and view pressure after you turn the pump On and after the engine finally starts.
After it starts, tap the accelerator while watching fuel pressure; if pressure drops replace the fuel filter under the passenger side along the rail.
Check spark plugs for condition and gap.
Does it idle smoothly and smooth under light acceleration??
Thanks for your reply.
I will borrow a gauge to check the pressure.
It runs ok in idle and when I gas standing still, and also on road. I will change the filter too.
Unfortunately everything takes time for me due to ill health. But now I have a plan. 🙂
The Corvette is a new car for me, so there is a lack of knowledge... haha...
From: Liliha Bakery stuffing my face with coco puffs!
Originally Posted by ihatebarkingdogs
85's don't cold start (first start of the day) very well if the Cold Start Injector (CSI) isn't functioning. The CSI is functional up to 95 deg F coolant temp, which isn't all that "cold". My 85 fires at a flick of the key, even if it hasn't been started in months. The CSI is protected by the CRANK fuse in the fuse block. Start by checking that fuse.
Originally Posted by SloJo
When does this problem occur? When it's cold, when it's hot, or anytime you try to start it?
Yup...how's restarting once the engine has warmed up to operating temperature???
Hi,
i need to pause my quest due to my health.
I will continue when more fit.
cheers/Stefan
Hello.
Please find an update of my crank issue.
It´s some kind of summary of a lot of 5-10 minutes visits to the garage, that´s unfortunately all I cope.
And I check the Haynes, Chilton and the Corvette Shop Manual, lots of reading....
It behaves the same wether or not I have the FPR fitted. I have no current to the pump via the FPR.
But the pump works, I tested it "off-line" with 12volts. Doing that I primed "manually", then tried to start - and success.
Normal cranking and start!
So I´m pretty sure that the FPR is incorrectly wired. Now it´s just the challange to get it right , I hope.
If I can´t find the fault, I can have a separate lead to prime it "manually". But I prefer to get it right.
I will report progress, but it will take some time. It´s not the season for Corvette driving anyway, -1 to -10 Celsius.
Hello.
Please find an update of my crank issue.
It´s some kind of summary of a lot of 5-10 minutes visits to the garage, that´s unfortunately all I cope.
And I check the Haynes, Chilton and the Corvette Shop Manual, lots of reading....
It behaves the same wether or not I have the FPR fitted. I have no current to the pump via the FPR.
But the pump works, I tested it "off-line" with 12volts. Doing that I primed "manually", then tried to start - and success.
Normal cranking and start!
So I´m pretty sure that the FPR is incorrectly wired. Now it´s just the challange to get it right , I hope.
If I can´t find the fault, I can have a separate lead to prime it "manually". But I prefer to get it right.
I will report progress, but it will take some time. It´s not the season for Corvette driving anyway, -1 to -10 Celsius.
All the best
/Stefan
Sounds like your relay is faulty. They are cheap enough - replace it. Doesn't necessarily mean it is incorrectly wired, just pooched.
Sounds like your relay is faulty. They are cheap enough - replace it. Doesn't necessarily mean it is incorrectly wired, just pooched.
Hi,
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... 😂
This schematic is for 1984 but the fuel pump and relay it is the same on the 1985.
The oil pressure switch is a 'limp home' function if the fuel pump relay goes bad.
Fuel pump should prime when turning on ignition. Then it should be on while cranking and engine running. The oil pressure switch is not needed.
If fuel pump realy is not engaged the pump will start when you get oil pressure and then run as normal. In this case it would normally take longer time to get oil pressure and fuel on a warm engine.
With ignition off, by applying +12V to pin G you should hear the fuel pump start.
Fuel pump relay is located near brake booster.
If you have 12V on ALDL pin G while engine is running then the realy is not even trying to engage. ( relay coil or ECM output )
Measure voltage pin B to C on relay socket while turning ignition on to check ECM output.
This schematic is for 1984 but the fuel pump and relay it is the same on the 1985.
The oil pressure switch is a 'limp home' function if the fuel pump relay goes bad.
Fuel pump should prime when turning on ignition. Then it should be on while cranking and engine running. The oil pressure switch is not needed.
If fuel pump realy is not engaged the pump will start when you get oil pressure and then run as normal. In this case it would normally take longer time to get oil pressure and fuel on a warm engine.
With ignition off, by applying +12V to pin G you should hear the fuel pump start.
Fuel pump relay is located near brake booster.
If you have 12V on ALDL pin G while engine is running then the realy is not even trying to engage. ( relay coil or ECM output )
Measure voltage pin B to C on relay socket while turning ignition on to check ECM output.
Hi,
(Mina föräldrar har stuga på Alnö 😁, men jag bor i Göteborg)
Thanks, perfect.
I will try to get help to measure.
I have tried the "G pin", but the pump is not running.
That is also why I suspect faulty wiring.
To test the pump I used a separate 12v.
The connector at the pump, the mid pin, what is that?
Maybe it's visible at the schematic you attached, but I look on the mobile right now and its so small... 😂
I will check on the laptop later.
A friend of mine will help me to check the connections at the relay. If I don't remember wrong there are pins A to E?
I have to check which wires should go to which pin.
Long crank time, priming?
