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Guest Message by DevFuse

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a gm problem

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8 replies to this topic

#1 thepenguin


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Posted 01 August 2007 - 06:12 PM

I got a 91 corvette in the shop.. this thing will not dile for crap once it warms up. its got 42 psi of fuel pressure on a hot soak and 32 while running. it has a oem distributor new fuel filter, plugs and wires, and even a new crank sensor.. still running like crap.. exhaust isn't clogged. mass air flow is working, iac working fine baros good ect is good the only thing I got to go on at this point is when you unplug one injector on either bank it smooths out.. it has two injector driver modules on two seperate circuits. they don't even share a common ground which I checked on both. I am at my whits end on this thing I really want to unplug an injector and give it back to the customer. please help:mad:

#2 nipper


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Posted 01 August 2007 - 08:27 PM

bad injectors causing it to run rich and flood at idle ?


#3 nipper


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Posted 01 August 2007 - 08:35 PM

Thinking more, maybe a shorted injector? i am assuming there is a common feed to the injectors, and they low side of the injectors go to the module or ecu?

look for what is common to both sides. removing one injector power from either side smooths it out. This make me think its electrical. Does it matter which plug you pull off. Removing a spark plug wire, does the same thing happen? If not, i would look at the FI electrical, as opposed to a sensor


#4 thepenguin


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Posted 01 August 2007 - 08:50 PM

ok I am still at work. it doesn't matter what plug I pull. I am going to scope test the fuel pump make sure it has a cisp signal and power feed. I know its an electrical issue now the problem what electrical feeds both injector banks and does not set a check engine light. I will let yall know if I find anything more but my heads starting to hurt from beating it agnist the wall I going home

#5 nipper


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Posted 01 August 2007 - 08:54 PM

CEL in OBD I cars esepcially american ones that used annoying diagnostics is not as good a tool as obdII.

Check the injectors when the car is hot to see if they are shorted to ground internally.

A electrical fault may not show up cold.




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Posted 01 August 2007 - 08:55 PM

Not to be a futher burden. But its an obd1 base car. It could be a number things and not set off a cel.

#7 Nug


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Posted 24 September 2007 - 09:16 PM

First of all, this car has something like 11 ground wires. They all need to be there, and be secure.

Second, the idle speed needs to be correct. 550-575 rpm.

Third, check the TPS voltage. Should be around .50 volt. Check your manual.

Fourth, check the base ignition timing. The computer assumes that the timing is at a certain baseline setting. If it is not, it will not run right. Check your manual on how to do this correctly.

The above must be correct before you start throwing money and parts at it. Do this stuff first.

More tips:

A classic goof is mixing the wires for the knock sensor and the coolant temperature/fan switch sending unit on the passenger side. The blue wire goes to the knock sensor, the green to the temp/ fan sensor. Reverse these and you'll get a code 42 and/or 43.

Lots of mysterious problems can be traced back to bad batteries, and crappy connections on battery cables. Test the battery, and do voltage drop tests on the cables to see if they are good. If there is corrosion, replace the whole cable instead of cutting the end off and splicing because the corrosion can wick up into the cable.

****All of the preceding information was pulled from a derelict Car Craft magazine sitting on my bathroom floor****

#8 hatchsub


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Posted 26 September 2007 - 06:32 PM

In both of the IROCs that ive had i have had to replace the computers. I guess its just getting to that time when the computer needs replacing. Do a slap test ..as in hit the computer with your hand while the car is running an see if it affects the idle. This is a speed density car right? Or did the corvette keep the MAF sensor and only the camaro go to speed density? If so could the map ( i think thats the right sensor) be causeing this problem?

#9 4x4_Welder


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Posted 28 September 2007 - 04:01 PM

This car has data streaming, do you have the right scanner for it?
What are the readings for:
O2s rich/lean
Fuel trim
TPS volts

Post up the results, I'm thinking the cts is off something else is making the computer richen it up.

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