I have been having trouble with starting my 95 TA. I have cleaned my injectors and have determined they are working fine as well as the fuel pump. OK so I hooked those injector lights into the injector harness and have discovered that if the car takes 5 seconds of cranking to start the car, the injectors dont start to operate until a millisecond before it fires off. Why wont the injectors jet electricity while cranking? This problem is intermitent, it will start immediately if tried within 5 minutes of turning off motor. Someone said maybe its the opticrap, but it is fairly new, the car operates fine will running and the opticrap as far as I can tell by diagrams has nothing to do with injector firing. Any help would be appreciated. Thanks

 

Usually long cranking problems are fuel related but differently than you had anticipated. Usually they are from flooding of the intake or from fuel draining back toward the tank.

There are 2 common causes of flooding in the intake, leaky injectors and a leaky fuel pressure regulator. You cleaned the injectors so let's assume they aren't leaking. If the regulator has a hole in it, it would have fuel in the vac line to the intake. See if the vac line to the FPR has fuel in it. This would also cause the fuel economy to go to crap. So you should know if the mileage is off. Another thing to help diagnose this condition would be to hold the throttle to WO when cranking it over. If it starts easier (quicker) you know it's from flooding. A leaky FPR would also cause the plugs on the passenger side to foul much more so than the others.

The other common problem is fuel drainage away from the fuel rails and back toward the tank. In a stock system, this is usually caused by a bad check ball in the fuel pump. After the engine is shut down, the fuel pressure will drop quickly and the fuel will drain back from the engine into the tank. One way to help in diagnosing this problem is to turn key on engine off KOEO for 2 seconds and then off. Do this 5 times before finally attempting to start the engine. If drain back is the problem, this will let you know.

Incidently, both problems can be seen with a fuel pressure gage connected to the fuel rail. The pressure will drop fast once the engine is shut down. Rarely the cause can be ignition, but the fuel problem is much easier and cheaper to eliminate as the cause before going on from there.

Oh yeah, please put the particulars of your vehicle in a signature.

Dave

 

The optispark has to provide a signal from the optical sensor. It functions like a crank trigger. I don't know the details, or how to test it, but opti sounds right to me.

Z28

 

I have already tested the fuel pressure and it goes from around 40 psi to 10 over the course of five minutes but will immediately go to 45 the second I turn the iginition on. The fuel is there but I am not getting an electrical signal to my injectors until the car starts, it should do this while cranking. I dont believe fuel is a problem as far as leakage or running rich. I have changed all plugs and they all look good and the car does not smell like excess fuel. I am not getting an electrical signal to my fuel injectors and I dont know why. What could cause this, the ecu, what controls the firing of the injectors.

 

If the PCM doesn't see the low resolution pulse from the Opti, it won't activate the injectors or restart the fuel pump. If that was the problem, you would get a "stored" code for the PCM not seeing the Opti signal for the period before the engine starts. Have you scanned the PCM for stored codes?

As mentioned above, it would help if you included the specifics of your car in a signature... year, trans type and any major mods. It's essential when you ask a tech question, since not all LT1's are identical.

 

I have scanned the ecu and found no codes but after long periods of driving the SES light comes on though car runs the same. I am only not getting electricity to the injectors on start up and not all the time. Sometimes she fires up the first crank. How can I check the low res signal. Pull the connector off the top of the opti and use a voltmeter. If so which wire in the connector is the low res , high res and whatever else is there. I wouldnt ask accept that I cant find this info anywhere, chiltons, internet, car forums, mechanic. No one has a clue. Thanks

 

If the SES light is coming on, you will have a "stored" code, at least if you scan it before you drive with maybe 50 drive-cycles and it self-clears. What are you scanning it with? I'm sure you are aware your 1995 has a "bastard" ALDL connector that requires a special connector, and an OBD-I scanner,

Shoebox has the complete 1995 A4 wiring diagrams on his Tech Pages website. I think he has a "how to verify the Opti signals" procedure on there as well. If you haven't ofund Shoebox's stuff yet, here's the link - bookmark it because it is probably the best source of this kind of info outside of GM.

http://shbox.com/1/4th_gen_tech1.html

 

Checked the codes with a mastach cable and datamaster. I recorded for about 3 minutes and then checked and the info said that there was no codes, it shows all the codes and marks them with either red for a code or green for no code, mine were all green. Performed the test three times same results. Also I found today that I am getting leakage at my fuel pressure regulator into my vacuum very slowly. Could this cause the injectors not to fire off. I am not sure if I have two seperate problems one being the injectors and one being the fuel pressure regulator or if they are related. If anyone knows let me know, if not by friday I will have a new fuel pressure regulator on.

 

slopok has already explained the issue with fuel in the vacuum line. The FPR needs to be replaced in that case. That would explain the slow start and related problems.

But a leaking FPR will not cause the injectors not to fire. How did you determine they are not firing "until a millisecond before it fires off"?

You might want to try another scanner on it.

 

I used a noid light which is the way you test at the harness. It showed a delay in the electrical firing of the injector. I will replace the FPR and give everyone a report back. I am hoping whatever is happening is somehow related. At that point I will then recheck with the scanner. I talked with a mechanic and he said FPR's dont usually throw codes on the LT1's and that he has seen them display the SES light without codes on numerous occasions. Thanks for all the help!

 

There is no code for the FPR. The PCM has no way to "see" the fuel pressure. Has no way to know its faulty. Any codes would be those that result from incorrect fuel pressure, like "rich" or "lean" codes.

I've been doing scans on these cars for more than 8 years, and have never found one that didn't store a code when the SES light came on. I have read a few reports here, but chalk it up to other issues.