Sarah's 1991 Camaro

[TransAmDan]

Are you able to monitor the voltage at the pink and black injector supply wires during cranking? If there is an HR connection the voltage would drop as the injectors pull current.

There is a plug that connects all the injectors to the wiring harness, I manage to get that apart, 6 wires, and all look very clean. Its a waterproof connector, but should be able to put a probe in there to measure the volts on the injector. The fuse that supply's them is under the dash, but I think it would be best to measure as near to the injectors as possible.

 

[TransAmDan]

Do you have a workshop manual? Is the regulator before the fuel rails or on the return?
Fairly sure I have a Haynes manual covering this engine so I might have to dig it out and see what useful info might help you?

Yes I have a manual, not looked at the mechanical positions of things, just wiring. Peaking through the gaps in the intake there is something circular on the fuel rails, so that may be the pressure regulator, you may find it quicker than me in the manual. Any info is useful.

A lot of progress has been made, at least the pump is working now, and proved many things isn't the issue. Its all good fun.

 

[Will]

There is a plug that connects all the injectors to the wiring harness, I manage to get that apart, 6 wires, and all look very clean. Its a waterproof connector, but should be able to put a probe in there to measure the volts on the injector. The fuse that supply's them is under the dash, but I think it would be best to measure as near to the injectors as possible.

OK. Yeah, the closer to the injectors the better, then work backwards in the supply line if the voltage measured at that point with a multimeter is low.
Looking again at your scope trace, the ECU looks to be pulling them to ground OK, but the mean DC in-between the pulses appears to he hovering at around 9-10 volts. That's what would make me check the integrity of the supply voltage. There are spikes up to about 18 volts but that's probably back EMF from the injectors. I've read that they can pull up to 6 amps each, so the supply needs to be healthy.

 

[AmericanThunder]

Have you pulled an injector? Verifying it’s spraying would be easy. It could be that everything works as it should but the injectors are gummed up. All 6 is unlikely but worth checking.

 

[TransAmDan]

Have you pulled an injector? Verifying it’s spraying would be easy. It could be that everything works as it should but the injectors are gummed up. All 6 is unlikely but worth checking.

Not yet, but that was my plan in post #36. I agree it would be unlikely for all 6 to be blocked, something is going on. Perhaps common 12V to them, fuel blockage, fuel pressure regulator. I'll need to dismantle the intake to investigate any of these, so perhaps a job for tonight if I get time.

Sprayed some rust buster on the bolts so it can settle in for the day. The intake is a two parts, the top half comes off with the throttle body. This should reveal the fuel rails and injectors. The injectors are well burried.

Below is a close up photo of the one above with better lighting. Notice the Red and Green wires in the middle of the photo, this is the fuel injector plug, this is the one I can see the best out of all 6. See how deep it is in there. Its gotta be done, all part of the elimination/testing.

 

[AmericanThunder]

Some more thoughts.
You say you have good pressure at the fuel rail but what is that pressure? I reckon you need 45psi +. That pressure could drop whilst cranking unless the fuel pump is running during the cranking process. You know the fuel pump primes during key on/off but does it run during the cranking process?
You really need a fuel pressure gauge to see what’s going on there and I’m not sure I would discount the pump just yet.

 

[AmericanThunder]

Any chance the timing chain has slipped?

 

[AmericanThunder]

Ok been studying the wiring diagrams.
GM typically switches on the negative side of the circuit. It shows a 12v ign voltage through two fuses (1 per bank), to the injectors. The other wire of the injectors goes back to the PCM which grounds them, presumably at the point they need to fire.
Have you found those fuses or confirmed 12v at the injectors?

 

[TransAmDan]

Some more thoughts.
You say you have good pressure at the fuel rail but what is that pressure? I reckon you need 45psi +. That pressure could drop whilst cranking unless the fuel pump is running during the cranking process. You know the fuel pump primes during key on/off but does it run during the cranking process?
You really need a fuel pressure gauge to see what’s going on there and I’m not sure I would discount the pump just yet.

Even if it was 20psi some fuel should still get through. There is power to the pump while cranking, confirmed in the occiliscope measurement.

 

[TransAmDan]

Ok been studying the wiring diagrams.
GM typically switches on the negative side of the circuit. It shows a 12v ign voltage through two fuses (1 per bank), to the injectors. The other wire of the injectors goes back to the PCM which grounds them, presumably at the point they need to fire.
Have you found those fuses or confirmed 12v at the injectors?

Correct, GM switches the negative side. Measured this in the occiliscope reading. Can see the voltage going high when not being pulled low showing 12V is passing through the fuel injector coils back to the ECU where I was measureing it. However is the 12V a good 12V?, I wont know until i take the intake off. The 6pin connector to power the inectors appears to look okay with a volt meter when not cranking, not verified while cranking.
I can confirm that both fuses are good, this are under the dash on the drivers side.

I think once this intake is off this will answer a lot of questions. I'll remove the main HT lead while cranking as will no intake it will try to go full throttle.

 

[TransAmDan]

Throttle body connected to coolant pipes I can leave them attached.

The fuel rail. You can see the 6 injectors and the schrader I was pressing to release fuel. Notice the round valve type thing with a vacuum hose, notices the damage on the vacuum hose, can this stop the fuel rail delivering fuel.
If that is some sort of vacuum controlled pressure valve could it be returning all fuel to the tank and so none is passing through the rails? Its odd it's not at the same end as the incoming fuel, perhaps there is something fancy in the rail to stop fuel getting to the injectors.

Having lunch now, may have another play later.

 

[July92RS]

That's the Regulator and it needs vacuum,,,be taking the top off that and checking the diaphragm to see if its split,,a bit like accelerator pomp on a carb engine,

 

[AmericanThunder]

That vacuum hose looks melted! How did that happen?
Anyway, that could well be the cause of your problems. The fuel delivery is directly proportionate to engine vacuum.
Hope you have intake manifold gaskets or they came off nicely?

 

[TransAmDan]

That vacuum hose looks melted! How did that happen?
Anyway, that could well be the cause of your problems. The fuel delivery is directly proportionate to engine vacuum.
Hope you have intake manifold gaskets or they came off nicely?

No new manifold gaskets, it came apart easily and needed to be done. I'll check later.
Yes that pipe does look melted, it's the first time I have taken this off. Perhaps nibbled by mice, very odd. I agree, could well be the issue.
Next it to find a right angle vacuum connector.

 

[AmericanThunder]

No new manifold gaskets, it came apart easily and needed to be done. I'll check later.
Yes that pipe does look melted, it's the first time I have taken this off. Perhaps nibbled by mice, very odd. I agree, could well be the issue.
Next it to find a right angle vacuum connector.

It’s very likely to be the issue. No fuel will be delivered in the absence of that vacuum signal.
I wouldn’t worry about finding the right right-angle piece, you could just use a piece of flexi vacuum hose.
Mice nibbling doesn’t work with the timing of it running, being welded, not running though so very curious.

 

[TransAmDan]

Looks intact. When taking it apart it did pop a bit, so hoping something was hammed and it's now freed up.

Replaced the vacuum joint. No leaks anywhere that I can see, although the vacuum system has been played with on this car, pipes going off to other places and multiple joins.

After putting it back together, joined a vacuum hose direct to this, I could suck and it would pull a vacuum, no leaks. Couldn't feel movement in the disphram, but perhaps the pressure would be too high for me to budge.

With fingers crossed it didn't start, but still more tests to do, like testing the injectors.

 

[AmericanThunder]

Updates?

 

[renchero]

when i put my p100 back on the road i had a lot of electrical problems it was corrosion on the fuses i had 12v on my volt meter
but lost it when under load

 

[AmericanThunder]

when i put my p100 back on the road i had a lot of electrical problems it was corrosion on the fuses i had 12v on my volt meter
but lost it when under load

Cars don’t like to be stored (unless perfect conditions) but this problem dates back many years to when the welding was done and the car was running ok then. Whilst there may be electrical gremlins rearing their head, the actual issue has yet to be found. Then again with an older car that’s been played with who knows what problems have been introduced!
I’m still leaning towards fuel delivery and want to see fuel pressure during cranking.

 

[TransAmDan]

Updates?

Nope,nothing yet, may have a play tomorrow.