Run the MAF diagnostics first, it seems to be the problem. The tap test is not all telling on these MAFs, so the testing from the FSM has to be done. The code 15 is a concern also, but first things first. Get the correct FSM, it will pay for itself. I also believe you have to start with a known baseline on the the basic maintenance, a complete tune up including the o2 sensor, fresh gas, oil change and the coolant changed and/or topped off. Also check your fuel pressure. Tackle the MAF problem, coolant code and then other codes. The egr can cause idle problems but not the problems your having with drivability.

Gary

 

Does anyone know if the codes are the same for 85's and 87's? I am looking at this 87 FSM, just trying to make sure I am not wasting my time.

 

OK, that was just a quick test. If the wire glowed, the test was over and the MAF was bad. Time to go a little deeper.

1. On the wire harness to the MAF, connect a voltmeter between Terminal A and Terminal E. These are the two end terminals on the connector. A is a black wire and E is a red wire.
2. Turn ignition on (engine stopped) for 10 seconds. Turn ignition off and immediately look at voltmeter. Voltage should stay above 10 volts for 4-8 seconds. If it does not, the burn-off module is bad. If it does, proceed to the next step.
3. Move voltmeter from Terminal E to Terminal D (Blue wire). Turn ignition on and check voltage. Voltage should be less than 1 volt.

Report back

 

I didn't see any voltage drop across those ever...I am pretty sure I was doing ti right.

 

I am guessing I have a problem with a wire; power getting to the connector. I will check for a volage drop across my wires if I can figure out where they go to.

 

Did you get voltage at all?

 

The red wire (Terminal E) goes to the MAF Burn-Off Module. The module is located behind the dash on the passenger side.

 

4.9V on the center pin that is all

 

The center pin is the 5v reference signal from the ECM. If you did not get any voltage on pin E, then the burn-off module appears to be faulty. It supplies 12v to pin E.

I have seen burn-off modules on eBay. But you might want to check a couple parts stores. Getting to the module is a pain. You have to remove the cushion referred to as the breadbox on the passenger side dash. I don't know how, mine was gone when I got the car. I suggest you start another thread and ask how. The breadbox can be replaced with a $50 plastic dash from Ecklers. That's what I have and it looks better.

 

Is there any additional testing I should do before I get the part? I still havent checked the wire because I wasn't sure which one it is.

 

This is where the troubleshooting chart in the FSM ends. If the MAF does not get 12v power to heat the wire, it does not work. The burn-off module supplies that voltage. I think you are done troubleshooting.

This why it is so important to look for codes and then use the shop manual to troubleshoot those codes. Swapping parts is not troubleshooting. It might work sometimes, but generally it costs a lot more. Keep in touch with me. If I can help more I will.

 

Ok, Thank you so much for all the help so far!

 

While I am looking for a solution for my burn-off module, does anyone have suggestions on how to approach my code 15?

 

I have a new thread related to my burn-off module issue, located here:
http://forums.corvetteforum.com/c4-t...post1583526874

Thank you all so much, any tips on my code #15 diagnosis/fix would be much appreciated!

 

Code 15 indicates a high signal voltage on the coolant sensor circuit. The coolant sensor uses a thermistor to control voltage to the ECM. The ECM supplies a 5v signal to the sensor. When the engine is cold, the resistance is high and the ECM sees a high voltage. As the coolant warms, the resistance becomes less and the voltage drops.

The code 15 will set if the signal voltage indicates a coolant temperature lower than -31 Deg F for 4 seconds.

Note there are 2 coolant sensors. One is for the ECM, the other is for the gauge on the dash. The ECM sensor is located on the front of the intake manifold. The other is on the driver side cylinder head.

I believe you can check the sensor by doing a resistance test. At -40 Deg F the resistance should be around 100,000 ohms. At +40 deg F the resistance should be around 7,500 ohms. I'm guessing you will see 100,000 ohms or greater. This would indicate the sensor is bad.

 

Update on my status, sorry I seem to have dropped off but I have been very busy with work.

MAF burnoff relay bought from cody here on the forum in the parts section, fast shipping, working part. I drove 4 miles and no CODE 34 anymore.

But my car decided it didn't want to start anymore. Pulled the alternator, got it tested, they told me it was failing, bought a new one put it in. Got it cranked up but it would only stay on if I gave it alot of gas.

I think my fuel pump is suspect, I had the pedal to the floor and I get no response (no gas coming in), I pulsate the gas pedal and it would go but cut off if I stopped giving gas immediately. I have a new one on the way and no how to fix it.

Worked on it again yesterday, swapped my Engine coolant Temp Sensor (I had a code 15), haven't checked the codes again, but I think I would need to get it running to see, I did get 5V on the connector going to the sensor so I think it was indeed the sensor that was bad.

Tried to crank it after cleaning the strainer and gas tank and putting in 7 new gallons of gas and it wouldn't even turn over, hit the starter and it tried, but I really think no gas was getting there, I couldn't hear the fuel pump cut on when my friend was trying to crank it and I had my ear up to the fuel tank opening. I did put voltage on the fuel pump direct from the battery when I had it pulled and it did turn on, seemed kinda flaky, but I think that was cause I had it rigged with wires I was holding so I kept disconnecting the power on accident.

I did not check if the power was getting to the fuel pump.
Any idea of if the fuel pump pulsator failing could be an issue? I guess its not necessary and can be replaced by a straight line, from a previous forum I read.

New fuel pump and starter in the mail, they are relatively cheap and the fuel pump is easy to swap at least.

Any thoughts, suggestions, and constructive criticism greatly appreciated.

It seems as if this car is breaking faster than I can fix it, I just want to see the light at the end of the tunnel.

 

Check for power at the pump, also get a fuel pressure gauge and check for fuel pressure.
If I remember correctly a bad pulsator will give you extended crank time but I don't believe it will cause a no start condition.

Gary

 

Check for power at the pump, also get a fuel pressure gauge and check for fuel pressure.
If I remember correctly a bad pulsator will give you extended crank time but I don't believe it will cause a no start condition.

Gary

 

Any updates?

 

You need some DEFINATE answers to these questions being presented by folks that know...

to do that, you need to STOP doing what you're doing until you get:



a real FSM 2 book set,.
a fuel pressure test gauge
a spark tester
a noid lite
DVM (in hand?)
some basic metric hand tools.

Never assume anything about the fuel system, its NOT at all like a carbed engine. pumping the pedal to keep it running is NOT helping it get gas...its giving the engine a short break to catch its breath after you've over-dosed it with air. If the fuel is NOT getting there it will NOT rev by giving it pedal...it will bog and maybe try to rev as the pedal returns to idle position. This is EFI....its high pressure gasoline that's sprayed at a precise time thru injectors that are told to open/close many times per minute. There is NO accelerator pump or other carb like things to go wrong...its 100% electric controlled and THAT is the primary source of failure. Mechanical failure is limited to the pump, the inj solenoids and the fuel regulator.

test the fuel pressure 1st. That MUST be close to 40 psi when the key is turned to ON or run but not starting the engine.

As far as the engine starting, please define that a little better.....does the starter turn the engine over but it does not fire? or does the starter do nothing, no click, nada?
or does nothing happen when the key is turned?
You have an early version of an anti-theft system that's notorious for no start conditions...that's why accurate descriptions of no start problems are important for accurate diagnosis.

So, get your fuel pressure to establish whether or not you have a pump/filter issue, or if the MAF is still at fault, or whatever else may be at fault.

IF there is NO other way to diagnose, unplug the MAF and run the engine. Drive it. This is forcing the ECM into a back-up run mode and will tell you real fast if its fuel system (it'll still run like it did before) or if it runs right now, then you KNOW its sensor or electrical related.

fuel pump fyi
The pump only runs 2 seconds when the key is turned to ON. The ECM will NOT allow it to run again until the engine is firing and running on its own. The ECM gets the 'ok' from the distributer to know the engine is running.

You CAN jumper the alcl to make the pump run if you have the FSM directions. I could tell you but you NEED the FSM to fix this car. Until then, you're guessing and just throwing parts hoping to get lucky. You won't. Trust me, we've ALL been down that road with Corvettes.
Even though this is a production Chevy and you'd think that its just like any other Chevy that rolled off a GM assembly line, it is NOT. The Vette has many systems that are unique and if you do not have the books you will never figure it out. I have seen people replace the entire fuel system including some unrelated electrical harness just because they did not know or understand that the pump only runs 2 seconds to prime the fuel rails at start-up. The book would have prevented that kind of expensive parts counter education. BTW, ANY parts store can read the codes. These pimple farmers that think they cannot,. are uneducated in OBD-I and flash codes and etc...You want a "code reader" .....NOT a scan tool. The zit ranchers do not know there is a difference...All they know is OBD-II...a totally different animal. OBD-I was before most parts guys were even born...like points. Go ask for a set of points for your distributer...you'll get the classic ...huh...blank stare.



FSM used books are $75 on fleabay. New will be about #$100.

Good luck...you;ll be glad you did all this...someday soon.