turns over but won't stay running - Team Camaro Tech
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post #1 of 9 (permalink) Old Jan 16th, 05, 04:54 AM Thread Starter
 
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87 camaro iroc-z
305 tpi 5.0L


We rebuild the transmission (T5) and put it back in. Then, when we went to start the car it would turn over, fire maybe 4-8 times and would die. We've checked fuel pressure both at the "on" position and during cranking and according to the shop manual it is ok. We've done the test with a wire in the diagnostic connector and it keeps flashing 12. We then unplugged sensors to test the ECM and it still only flashed 12. So, we replaced the ECM and tried again. Nothing changed. We've checked the starter- working and properly grounded. We've also checked most of the circuits- all working properly. We checked the cold start valve- works (injector light stayed on when plugged into it during crank).
When we went to check the fuel injectors with a test light, it would not flash. This is (according to the shop manual) supposed to flash a code error, and it isn't. We also checked the circuits for the fuel injector system- they work properly and are grounded correctly. The spark plugs fire properly.

We think the ECM isn't sending a signal to the fuel injectors.

Here's what we have tried already per the shop manual:

Diagnostic circuit checked: ok
Tested power to pins in ECM connector and ground to ECM connector: ok
fuel injector circuit tested: ok
injector noid light doen't light during crank
"fuel diagnosis" tests fuel pressure: ok (pressure equals 46- drops to 43)
crank fuse: ok
cold start valve: ok (lights when noid is attached)

When we unplug sensors (MAF, cold start) the ECM doesn't generate error codes (according to the service engine light flash test)- we only get code 12 over and over. We just replaced the ECM, however, and the results didn't change. We think teh problem is with the ECM generating the signal to the fuel injectors, but we don't know how to check on this (manual just says replace ECM).
For the injectors to fire, certain checks are done by the ECM:

pulse from distributor
throttle position
coolant temperature

These are the only test that we know of. If anyone knows of the other checks done by the ECM, that knowledge would be helpful too.

Thanks for the time and help with my problem!
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post #2 of 9 (permalink) Old Jan 16th, 05, 07:32 AM
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I'm not sure about the 87 motor, but does it have a crankshaft position sensor? If it does, it can cause the sympoms you are seeing. I know some GM motors (particularly front wheel drive V-6) in that era use a crankshaft position sensor.

Dave
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post #3 of 9 (permalink) Old Jan 16th, 05, 11:04 AM
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Code 12 for the ECM means its okay. The fuel injectors, two sets, pass side & drvr side, are powered by a relay each and a fuse to one side of the injectors. The other wire of the injector goes back to the ECM.

The ECM places a "low" on this wire, thus, creating a difference in potential and the injector opens for milliseconds. Only a "noid" light will show this event. One side of the engine is a green wire and a black wire, the other side is purple wire and a black wire.

As a test, you can measure the injector coi; resistance with a DMM, digital multimeter, and measure 12-14 ohms for each coil. Also, measure into the disconnected harness to be certain continuity to the ECM. Having power to one side of the injector and control voltage on the other side are important.

On the intake side, be sure the MAF meter is plugged in the circuit as well as the intake air. Plus, be sure the bellows has no holes and the intake track from MAF to the throttle body is "airtight."

It reads like the cold start injector is working good. Fuel pressure reads good. I'm sure in swapout of the chip, the operation went smooth and no bent pins, or, if the ECM is from a different vehicle, the chip was changed as the chip goes with the VIN, not the car.

Hopefully, you didn't crunch any wires from the wire harness when replacing the trans. The wire harness does come close to the b/housing & engine interface.

Be sure spark is going correctly to each cylinder and at the proper time. You didn't break any ground wires or leave any off did you? There are a few fusible links at the starter solenoid terminal with the posotive battery cable. There may be one broke.

ECM is not going to generate any codes until the engine is running. Pull the spark plugs, dry them off, blast each cylinder with shop air to dry out. Charge the battery. Reinstall plugs, mash throttle to the floor, and attempt to start. Retrace your steps through the trans swapout just to be sure you didn't miss anything or left something out. I wager it will run.

Oh, Welcome to the Club, Newbies buy the first round. You'll enjoy it here. Let us know what happens.

PS., Hopefully, the IGN position of the ignition switch is in good repair. I'd hate to read later the start ign signal is good, but the "run" position is bad.

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post #4 of 9 (permalink) Old Jan 16th, 05, 12:41 PM Thread Starter
 
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Thanks for the various advice. We are trying (no crankshaft sensor in this year, still checking electrical causes) the different ideas now and will get back in touch as soon as something turns up.
Oh, and ya, drinks on me.
Thanks!

PS: Could not bleeding the clutch cause any type of problem?
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post #5 of 9 (permalink) Old Jan 16th, 05, 04:27 PM Thread Starter
 
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We bled the clutch, changed all of the spark plugs, and found a sensor into the block (coolant) that was unplugged. After fixing those things, it still won't run. (no visible difference)

The spark plugs we took off had a small nub in the gap that wasn't like a standard flat spark plug (burns hotter?).We put standard plugs in (new- got them before we took off the old plugs).
Didn't help.

I'm running out of ideas. Thanks for the help so far though.
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post #6 of 9 (permalink) Old Jan 17th, 05, 01:58 AM
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Try looking at the injector fuses, spark plug electrode having a "dip" in the ground electrode signifies lots of mileage.

So you have an injector noid light, good. At the injector plug, either one, one wire will have battery voltage to ground, the other wire will be control voltage, either a high (close to battery voltage) or a low ( almost zero volts, maybe 0.5 VDC).

Its too bad you don't have spare distributor, then you could subtitute the OE dist and turn the sub dist by hand and listen for the injectors working.

Check the distributor connection. The ECM references the rpm signal to generate the inj pulses. If the TACH connection is loose, inj may not work, but, you will still have spark.

Keep us posted. Stay warm......
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post #7 of 9 (permalink) Old Jan 17th, 05, 12:22 PM
 
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could the distributor cap have gotten cracked?
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post #8 of 9 (permalink) Old Jan 18th, 05, 03:13 PM Thread Starter
 
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Thanks for all of the tips and support. As it turns out, when we took off the distributor cap we found the four-way connector unplugged. Sorry I didn't check for something that simple before, but I thought it wouldn't fire with any wires unplugged. Thanks again for the help though!

PS: Tranny runs sweet now!
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post #9 of 9 (permalink) Old Jan 19th, 05, 01:36 AM
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