Let me start by saying that my car has a noticeable stumble and miss in the low-mid rpm range.

I had the car scanned at the local dealership and it has the following codes:

I am not to worried about these as they were known issues before I went in:
26: EVAP system - forgot to reinstall the solenoid on rebuild, will do right away but I don't think this will cause a miss
27: EGR - permanently removed
29: AIR Pump- permanently removed

The ones that concern me are the following:
18: Injector circuit, pcm will disable the problem injector and shut it off - will cause a noticeable miss
41: Ignition control circuit - ckt 423 exceeds 4.6V when rpm's are less than 1500 - not really sure what this means, will it cause a miss?
48: MAF related - I have another maf that I will switch out, but I don't think this will cause a miss

So, the question is what course of action to take here? Should I buy a set of injectors? What do I do about 41? What does it mean?

Lastly, is there anyway to trick the computer into thinking that the EGR and Airpump are truly in place?

Thanks in advance for your help,
Ryan

 

You've got to include the year of your car with a question like this. 93 has different codes than 94/95. We can guess its a 94 or 95 from the MAF code.

Why not add a "signature", with basic info about your car - year, model, engine, tranny and any major mods? People need that kind of info to help you.

Test your injectors before playing parts replacement roulette.... it gets expensive.

Pull the harness connectors off all the injectors and verify the resistance of each injector is in the range of 12-15ohms. With the key on, make sure you have 12V at the pink wire on each injector connector. If you get good results with those tests, put a noid light on each injector to see if the PCM/wiring is supplying the ground pulse required to fire the injector. Alternatively, with the engine idling, pull the connector off the injectors one at a time, and see which one DOESN'T make it run worse. That will be the faulty injector.

DTC 41 indicates an open circuit in the ignition control system. Could be a faulty IC Module, or faulty wiring to the module. There's a diagnostic logic chart in the factory service manual. Find someone that can provide you with a copy.

DTC 48 indicates a problem with the MAF sensor electrical circuit. For starters, pull the harness connector off the MAF sensor, and key on test the pink wire for 12V, referenced to the white/black ground wire. With the engine running, you can also use a frequency meter to read the frequency for varying air flow, and compare it to the MAF calibration chart.

As far as the EVAP solenoid, either replace it, or put a resistor in the harness connector, same value as the solenoid you removed. Ditto with the EGR solenoid, which is what your code is for. There's an EGR code for "no flow" (DTC 32), but you aren't getting that one. The OBD-I diagnostic is not very sensitive.

With the OBD-I cars, as long as there is a good fuse in the AIR pump electrical circuit, it will not set a code, even if the pump and all the other components are removed.

 

Thanks Fred. Odd question - have you ever worked at Holley?

Ok, I will do what you said with the injectors, but from what I read, if I unplug an injector while the car is running, it will set code 18 and shut down that injector circuit. Is this not true?

For dtc 41 - Why does the car still run with a faulty icm or wiring to the icm? I do have a fsm on loan from the local dealership. I will try to diagnose this tonight.

For the maf one, where do I find these maf calibration charts and how do I measure the frequency of the maf?

I plan to borrow a nice multimeter from work today so I should be able to do all the diagnosis. Is there a way to check the injectors without purchasing a noid light?

Thanks again for your help and you are right with the car being a 94-5. Its a 95 M6 z28. How do I add a signature?

Ryan

 

Alright, I went through and checked everything and found some loose connections. Now I have no codes! Thanks for all your help.

Ryan

 

To add a "signature", go to the red bar at the top of the screen, left corner and click on "User CP". One of the drop down options will be "edit signature".

As you found out, the codes can be set by connection problems, which are often intermittent. A loose wire to the ICM can cause DTC 41 or 42, and the engine will still be running, but maybe missing once in a while.

You can measure the MAF output frequency with a frequency meter. Most moderate price multi-meters include frequency. I can send you a table of the stock MAF calibration table, frequency vs. air flow grams/sec. I need to add it to my online "scanner" writeup.

When you pull the connector off the injector, it will TEMPORARILY shut down the injector. Once you reconnect it, it will start to work again.