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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...
Then it could be the relay or wireing close to the relay. Measure that you have a 12V feed to the relay and try a jumper to FP pin on relay.
Then it could be the relay or wireing close to the relay. Measure that you have a 12V feed to the relay and try a jumper to FP pin on relay.
I'm having a short garage session again, I manage only short sessions due to ill health...
The relay have 12v, but
I haven't been able to measure the 2 sec pulse.
Out of curiosity I wanted to check the pump.
When I feed the pump separately with a battery the pump is running fine.
But if I feed 12v from the car, using ground of the car, it doesn't run.
I feed to the fuel pump connector, and ground from the car.
Do I make myself understandable? 🙄
Somehow it seems like ground is messing things up... ?
Om du ska köra pumpen från kontakten vid tanken så är A=jord och C=12V. Det är inte säkert att det fungerar att jorda bilen eftersom tankarmaturen kan vara isolerad från resten av jorden p.g.a. packning.
Men jag anser att du kan utesluta fel vid tanken eftersom pumpen fungerar när oletryckswitchen aktiveras.
Jag tycker att du ska undersöka kontakten till bränslepumpsreläet.
A - Tjock Röd - till bränslepump.
B - Smal Svart med vit rand - Jord
C - Smal Grön med vit rand - Signal från dator
D - Smal Röd - Till pinne G på ALDL kontakten
E - Tjock Orange - 12V från batteri
Om du kortsluter A till E så ska pumpen starta. Det är stiften längst ifrån varandra. Det är mellan dessa stift som oljetryckskontakten sitter.
Om det fungerar är nästa steg att kolla styrsignalen till reläet.
Mät B ( Svart vit ) ohm till jord. Det ska vara nära noll.
Mät spänning mellan C och B. Det ska bli 12V när datorn drar pumpen ( 2 sekunder ). Du kan även koppla en klen lampa, typ instrumentbelysning mellan stiften.
Jag fick laga min originalbox. Det var en transistor som drar reläet som hade pajjat. Den blev också svårstartad.
Kolla även att kontaktstiften ser bra ut. Det är inte helt ovanligt att kontaktstycket blir dåligt, att stiften tappar spänst.
Hi again,
Sorry for the stand still.
I managed to dislocate a knee in a bad way.
So my garage time is on halt for a while.
But I will be back! Thanks guys. 👍
/Stefan
I am sorry to hear about your knee, I guess your skiing is done for the rest of the season in Sweden! Be careful and Stay Healthy!
While reading the posts regarding the fuel pump not running I remember doing the same test for the same reason. On my C4 the fuel pump worked fine with power applied to the pump where the gas filler is. It turned out that my fuel pump relay was not getting enough voltage to make it hold. The reason I had the problems was because the fuse block was corroded as well as the Post that supplies the battery Power to Feed the Fusible Links. On my C4 there are 7 fusible Links that are powered at the post. All 7 Fusible Links Connectors had corrosion issues and after a good wire brushing I reassembled the post and covered it in battery Grease.
This made a low voltage situation where I was about 2 volts low at the dashboard. When I cleaned the post suddenly I had full battery power at all the fuses on the panel. Try activating the Fuel Pump Relay manually using 12 Vdc and see if that works.
My Corvette also developed a strange problem where it would develop the correct Fuel pressure But NOT the VOLUME of fuel needed. The gasoline today has ethanol in it here and it absorbs water like Brake Fluid does. My fuel Supply Line was Blocked off internally but with just a little fuel getting by the pressure looked okay but the engine would not rev properly. I verified the fuel amounts by measuring the fuel released over 5 seconds through the original line and a Rubber Bypass Line and the test was very easy to do. I ended up replacing both of the two fuel lines, 1 supply and 1 return line from the tank to the engine.
Like mentioned above, if you have the Pulsator still on the fuel line I would remove it and replace it with Fuel Hose designed for "Fuel Injection" and "Submersion in Fuel". I removed mine the first time the unit was taken out to install a new pump. The problem was it was not the fuel pump that caused my troubles. If your fuel pressure drops too quickly after shutdown then it will likely be either the Injectors or the Fuel Pressure Regulator, mine started getting worse so I replaced my injectors and that is when I learned that I had a leaky injector. I also found that my Cold Start Injector (9th Injector) was also leaking so it was replaced as well.
That is not all either, a previous Owner (Bubba) crimped some wires on the engine and he/she did a "terrible job". I had a loose connection that appeared okay until I removed the wire and checked for power. Bad connections or grounds are frequently a cause of problems for the early C4's. I still clean every connection and treat it with "DeOxIt" which really helps the connections stay good and cleans off all the corrosion on the contact.
Long cranking times are frequently Fuel related, but the other part that could aggravate the cold start process would be the Coolant Temperature Sensor (CTS). If your CTS is off it would clearly make your cold starting harder. Imagine that your CTS is telling the car it is 35*C when it is really -10* C. This would make the engine start up with NO choke or Cold Start Fuel Enrichment which would lead to longer crank times. It would be like starting a Car in the cold with no choke to help you.
If the CTS thinks it is -40* C the fuel enrichment would be "ON" and not turn off causing your engine to run very rich. This could make warm starts take longer than normal.
The CTS on my 1988 C4 is on the front of the intake plenum and has three wires feeding it. You measure the resistance between two of them and then compare it to the chart in your Factory Service Manual to get the temperature the sensor is indicating. By the way, CTS' go bad all the time and are not too expensive since they are small.
Last but not least Check the wires that feed your injectors. Each injector should have 12 Vdc on one side with the key "ON". When the computer wants the injector to release gasoline it will send a ground signal to the other side of the injector. If one of the wires that supplies ground (0 Vdc) is shorted to the engine block you would have an injector that constantly injects while the key is "ON". The wires are tiny and sit on top of a very hot running engine. On my C4 the insulation was breaking off in many places on each ground. They are worth checking.
Many electrical components use Pulse Width Modulation which makes measuring the voltage a bit harder. I use a tool called a "Power Probe 4" for working on my Corvette's electrical systems as it applies power or ground at the tip by the flip of a switch. Very, very handy Corvette tool!
Your Corvette is beautiful, it must be awesome having one in your part of the world!
P.S. Make sure nobody jacked your Corvette up crushing the fuel line, I have seen it happen on fuel lines and on brake lines where a lift operator picks it up from the wrong spots...Just another thought!
I am sorry to hear about your knee, I guess your skiing is done for the rest of the season in Sweden! Be careful and Stay Healthy!
While reading the posts regarding the fuel pump not running I remember doing the same test for the same reason. On my C4 the fuel pump worked fine with power applied to the pump where the gas filler is. It turned out that my fuel pump relay was not getting enough voltage to make it hold. The reason I had the problems was because the fuse block was corroded as well as the Post that supplies the battery Power to Feed the Fusible Links. On my C4 there are 7 fusible Links that are powered at the post. All 7 Fusible Links Connectors had corrosion issues and after a good wire brushing I reassembled the post and covered it in battery Grease.
This made a low voltage situation where I was about 2 volts low at the dashboard. When I cleaned the post suddenly I had full battery power at all the fuses on the panel. Try activating the Fuel Pump Relay manually using 12 Vdc and see if that works.
My Corvette also developed a strange problem where it would develop the correct Fuel pressure But NOT the VOLUME of fuel needed. The gasoline today has ethanol in it here and it absorbs water like Brake Fluid does. My fuel Supply Line was Blocked off internally but with just a little fuel getting by the pressure looked okay but the engine would not rev properly. I verified the fuel amounts by measuring the fuel released over 5 seconds through the original line and a Rubber Bypass Line and the test was very easy to do. I ended up replacing both of the two fuel lines, 1 supply and 1 return line from the tank to the engine.
Like mentioned above, if you have the Pulsator still on the fuel line I would remove it and replace it with Fuel Hose designed for "Fuel Injection" and "Submersion in Fuel". I removed mine the first time the unit was taken out to install a new pump. The problem was it was not the fuel pump that caused my troubles. If your fuel pressure drops too quickly after shutdown then it will likely be either the Injectors or the Fuel Pressure Regulator, mine started getting worse so I replaced my injectors and that is when I learned that I had a leaky injector. I also found that my Cold Start Injector (9th Injector) was also leaking so it was replaced as well.
That is not all either, a previous Owner (Bubba) crimped some wires on the engine and he/she did a "terrible job". I had a loose connection that appeared okay until I removed the wire and checked for power. Bad connections or grounds are frequently a cause of problems for the early C4's. I still clean every connection and treat it with "DeOxIt" which really helps the connections stay good and cleans off all the corrosion on the contact.
Long cranking times are frequently Fuel related, but the other part that could aggravate the cold start process would be the Coolant Temperature Sensor (CTS). If your CTS is off it would clearly make your cold starting harder. Imagine that your CTS is telling the car it is 35*C when it is really -10* C. This would make the engine start up with NO choke or Cold Start Fuel Enrichment which would lead to longer crank times. It would be like starting a Car in the cold with no choke to help you.
If the CTS thinks it is -40* C the fuel enrichment would be "ON" and not turn off causing your engine to run very rich. This could make warm starts take longer than normal.
The CTS on my 1988 C4 is on the front of the intake plenum and has three wires feeding it. You measure the resistance between two of them and then compare it to the chart in your Factory Service Manual to get the temperature the sensor is indicating. By the way, CTS' go bad all the time and are not too expensive since they are small.
Last but not least Check the wires that feed your injectors. Each injector should have 12 Vdc on one side with the key "ON". When the computer wants the injector to release gasoline it will send a ground signal to the other side of the injector. If one of the wires that supplies ground (0 Vdc) is shorted to the engine block you would have an injector that constantly injects while the key is "ON". The wires are tiny and sit on top of a very hot running engine. On my C4 the insulation was breaking off in many places on each ground. They are worth checking.
Many electrical components use Pulse Width Modulation which makes measuring the voltage a bit harder. I use a tool called a "Power Probe 4" for working on my Corvette's electrical systems as it applies power or ground at the tip by the flip of a switch. Very, very handy Corvette tool!
Your Corvette is beautiful, it must be awesome having one in your part of the world!
P.S. Make sure nobody jacked your Corvette up crushing the fuel line, I have seen it happen on fuel lines and on brake lines where a lift operator picks it up from the wrong spots...Just another thought!
Best Regards
Chris
Hi Chris,
Thanks for all the tips.
Embarrassing enough I dislocated my knee while closing the hood of the Corvette... 🤣
Yeah, I've understood that jacking up the C4 can cause damages, thank you. 👍
I'm more used to rough Jeeps, so I have to be more cautious.
When I'm 'back on track I will continue the detective work. I will update the thread.
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.
If the fuel pressure quickly decreases below the operating pressure after you shut the key off, then I think you have a bad check valve down in the fuel pump assembly. I think this is the problem that ztheusa was referring to in post #13 and #23. The check valve is allowing all the fuel line pressure to bleed out after the pump shuts down, which means every time you try to start the car the fuel pump has to run for an extended period to rebuild the pressure in the line between the tank and the FPR. You don't even have to run the engine to test this. Hook your pressure gauge up, then turn the key to RUN without even starting the engine. You'll hear the pump run and should see pressure build to around 40psi. Then turn the key OFF and watch the pressure. If it starts falling right away and reaches 0psi after a few seconds, that check valve is not holding pressure in the line. With this problem, the engine runs fine once the pump builds pressure, but it takes a while to build pressure. With the engine off, if you turn the key to RUN without starting the engine and let the fuel pump run 10 seconds or more, you can then crank the starter and it will probably start right up.
