I have a 1994 LT1 with about 180k on it. Ive been having this "issue" and havent had the best of luck trying to solve the problem. Its throwing a code 48 (Mass Air Flow Sensor Circuit). Car starts and drives fine. Randomly (usually at a stop light or while first moving, the car will cut out). I can put it in neutral and it starts right back up and everything's fine. It could cut out again at the next light or 10 stops down the road. (the car will drive fine, until the problem occurs, then it will just go down hill from there and keep occuring). I also have a code 28, which is the AIR pump circuit ( the relay for this is messed up and the fused is blown) Im from Florida so I dont have emissions to worry about so ive just left it. (im 99% sure this has no connection to the issue as its been like this and driven fine with the code 28 for well over a year). I have a new and the old MAF sensor ive tried them both and still the same problem. I was reading that it could possibly be the relay, I tried locating it on my car and it there is not one on the back firewall behind the battery. I found 3 relays on the passenger side (somewhat near the windshield washer fluid fill) I replaced them all just in case lol. I also found 2 mounted on the drivers side of the radiator (these were replaced as well). These are the only ones i am able to find on the car besides the messed up AIR one. After replacing them the car ran great for a few days/trips. And BOOM, happened again :smash: I have both of the shop service manuals for the car and followed the steps.

1. Clear DTC's/start/idle does DTC set?
It toke me a while but i did manage to get it to set eventually while sitting in the driveway. So yes

2. Connect voltmeter between term A and ground should read between 4-6volts, does it?
Yes it was reading just shy over 5 volts.

3. Measure voltage between harness connector terminals B and C Should be B + Is it?
Heres a question, im assuming that means it should have a positive volt? If so, no it has like -.19 volts.

4. Measure volt between terminal C and chasis ground, should be B+
(same as above)

So my options are

Open ignition feed circuit to MAF sensor (i believe this is it) or Open ground circuit to MAF sensor.

Now im not really sure where to go from here. I tried looking for a circuit diagram so i can find out where the ground is for the 339 circuit and am not having much luck. Also tried looking in the ignition section. I am basically not having much luck trying to locate where in the shop manual i need to go next.

I also looked for vacuum leaks couldn't find anything. tried the taping MAF sensor test wiggling wires, feeling around all the wires in the engine compartment to try and reoccur the problem and havent had any luck.
Car is bone stock, I have checked all the fuses (panel and underhood) and they are all fine. I would assume a ground short would blow one?


I apologize for the long post (trying to give as much info as i can up front) and I appreciate you taking the time to read this and thank you ahead of time for any insight or information you can provide me.
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First off, book two should have the breakouts for the that harness.

Wish I could help you but I really can't. I have an '89, which is much different than yours, but every time I had maf codes it was the relay. A cheap part to try, if your car has relays similar to mine. Beyond that, I don't know and I have no experience with an LT1.

I don't have much to offer either. But Welcome aboard.

I only have a 92 FSM (no MAF), but could use a bit more info. Cuts out? Is this "fully shuts off and must be restarted"? I think you answered this but.
Does it restart easily?
Does this happen after the car is fully warmed up, driven lie 10 minutes? Does it do it while the engine is cool and being warmed up?
When it goes downhill, does it cut out frequently or does the engine run bad?
Does this happen only at stoplights or can it happen at other RPMs.
Will the car rev above 4,000 or so?

The MAF may be a contributor but, I would think it wouldn't cut out the engine unless this condition is cusing the ECM to send the wrong info to the IAC.
The Idle Air Control could also have a wiring problem.
The injectors or their relay may have a problem.
The Ignition Control Module could have a wiring problem but, I dought it is at fault since they usually crap out under hest and need to cool down to work again.

How old is the Opti? A bad opti can cut off the engine and the restart for quite a while before throwing a code.

Also, DTC 28 on the list I have (corvetteactioncenter) says it's "transmission range pressure switch fault", DTC 29 is the AR pump.

Thank you for the replys I appreciate it.

By cuts out, i mean fully shuts off and must be restarted. It restarts easily right away no problems.
I guess i would say it generally happens after the engine has been warmed up.
I have had it stall a few times while cool, but usually its fine for the a trip somewhere and then the problem occurs on the return trip home. Usually car only sitting for less than an hour, so its still warmed up i guess.
Im from south Florida, so I am afraid i dont have much "hills" to have driven it on or much less to even test it out.
This happens at a stop sign or stop light as the car is sitting idle, or right before take off. I have had it cut out when doing a U turn two or 3 times, This was just barely over idle speed tho.
I belive the car will rev above 4k, I will give it a test it out tomorrow. When at WOT I have noticed a nice size black smoke cloud from the exhaust tho (I know this is fuel).
The opti was replaced shortly before i purchased the vech 3 years ago, I have put probably 6k-7k miles on the car since then. So id say it has less than 10k on it.
That was a mistype it is indeed a code 29, for the air pump.

Thanks again for your help.

So, you can pretty much eliminate the opti.
The black smoke may be part of the MAF problem, punching it to WOT with everything right shouldn't have black smoke. It may have a gray/brown puff but that's just crap built up in the exhaust from slower driving.

The cut out may be the IAC or it's wiring since it's only at low speed.

There are charts in the FSM in section 6B right after the last code ref. in 6A. Check "Rough idle, unstable idle,stalling"
Also check the chart for Idle Air Control in 6E.

Have you done a fuel pressure test? Ohmed the injectors?

Good Luck

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No B+ means the signal should be the same as the current battery voltage.



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You will not find the ground for wire 339 as that is the power wire. It joins back in at S115 with the EVAP, EGR Solenoid, TPS interface module and the CAGS 2-3 blockout (if equipped)

The ground is Number 108 and it is at the passenger side front head.

My suggestion is to repin the harness and create a new power feed and a new ground. And see if the car runs correctly. The yellow wire is the signal wire going to the PCM.

chase the harness back... I will bet money that you have a serious issue where it goes to the back of the engine.

Once I get home ill check the manual and take a look at the IAC. I was also told to try disconnecting the MAF sensor and drive around and see if the problem reoccurred (and if it didn't it was probably the sensor itself). I did so and I did several trips yesterday for last minute valentines day and didn't have the slightest hint of a problem. (car just didn't have any power, but im sure this is normal.)

?

camaro guys complain alot about the power wire to the maf.. if i remember correctly its the pink wire.

I went outta town for a few weeks, I ohm'd the injectors they were all around 12.9-13. I have not checked the fuel pressure yet Ill have to go buy a gauge from autozone or something. I checked all the grounds and cleaned them up with some contact cleaner.

What I was talking about before was that I was told a way to check to see if it was the MAF was to disconnect it and try driving around to see if it fixed the problem. Well I did this and the car runs great. The MAF is new so I do not believe it is the problem. With the MAF disconnected is the IAC valve still being used? Wondering what else in the car is being affected by disconnecting the MAF.

I forgot to add earlier, there are more relays under the passengers side knee pad.

The IAC is being used. It might piggy back on the circuit, but it is an independent sensor.

Well, the MAF tells the ECU how much air is coming in and how fast. So without it connected, the engine is running off the built in tables. This means something in the harness is telling the computer some bad info.

I wish I had a 94 HSM, but I don't... I will check my Corvette EFI and Electronic Ignition book, it covers up to 2001.