lancerus

Hi - I'm looking for some advise on MAF errors. I have an 87 IROC with the 5.7L. Some performance work was done before I bought the car (chip, thermostat, flowmaster exhaust) - otherwise (as far as I know) the car is stock with 45k miles on the engine.

Last year it started throwing a MAF High code (code #33). I purchased a SnapOn MT2500 analyzer, and sure enough - there are 2 values shown, a MAF value, and an "airflow" value. The airflow value was locked high (a reading of about 48), the MAF value however properly tracked airflow differences if I revved the engine.

Trying to get ready for this year's PowerTour - so far I've replaced the MAF with a Granatelli unit. The TPS had been replaced about 5k miles ago. When I first installed the new MAF - I threw a MAF Low error (code 34). SnapON scanner in diagnostic mode showed that the (like before) the MAF value tracked engine rev, but the "airflow" value was locked solid at 6. I swapped back and forth btwn the old and the new MAF - and the code 34 went away. I'm assuming I had a bad connection (?). After the code cleared - looking at the SnapON again, and I see that the MAF and "airflow" values track about the same. about 6 at idle, and shooting up the 30-40 when I rev the engine. At this point the engine was running great - extremely responsive and producing full power.

This weekend I took the car out for a long drive. 30 miles into it the engine light came on. Brought the car back home - hooked up the SnapON - and I'm reading a MAF High error again. The "airflow" value is again locked at about 48, but the MAF value still seems to be functioning correctly. The car was otherwise running fine except that it felt slightly "de-tuned". I continued to use the car like that for some errands - when suddenly the car started bucking, engine fluttering, and a total loss of power. This happened 2-3 times within 5 miles where I had to pull over. Shutting the car off for about 15 minutes seemed to clear the loss of power issue and I was able to get the car back home. The ONLY code shown is still the MAF High code (#33).

My questions are:
-) where do I start? I'm at a loss of what to do next.
-) I can understand that the engine wont run correctly when the computer is throwing codes - but the total loss of power feels like there is something else going on in addition to the MAF code? I cant reproduce this problem at will, so I'm not sure how to diagnose it?
-) is anyone else familiar with the MT2500 scanner and the information it is reading off of the car computer? What is the difference between the MAF value I'm reading vs the "airflow" value that I'm reading? That almost implies that there are (2) sensors here, or (2) distinct values that the MAF is responsible for producing to the computer ?

Any help/advise would be greatly appreciated. Thanks!

3.8TransAM

Believe one MAF valuie is what is stated in the code or expected.

The other is the actual gm/s the sensor is seeing. Its been a long time since I have had a MAF car on my MT2500.

Have u investigated your MAF burnoff relay yet?

Its a possibility if it is occuring to you with two different sensors.

Also , is your air intake 100% sealed from the MAF to the TB?

There is tons of info here on all the above, but the search is temporarily down. Hopefully one of the MAF guys pops in, I dont have an older manual to help u with.

later
Jeremy

lancerus

Yes - I noticed the search was down :-(

I'm ordering both relays today, hopefully will have them by the weekend. They are cheap enough where i assume i have nothing to lose replacing them. None of the local parts stores knew what I was talking about when I asked for the relays.

One more data point - with my old MAF - the car was a BEAR to start when it was cold. Start/Stall/Start/Stall - once it got slightly warmed up - it would continue to run and would restart easy. With the new MAF - my cold start problems completely went away. I took that as a hopeful sign that my old MAF was indeed failing. Even with the MAF high error lit now, the car still starts easy.

The old maf - the silicone was pealed away on the electonics cover. The screen inside the maf was covered with a thick film (kinda like a mixture of oil and dirt). Unfortunately the old maf dropped about 1 foot in my garage and broke the connector area, so I cant switch back to it now for comparisons.

As far as i can tell - I have a good seal btwn the MAF and the TB. Or at least there isnt anything visually obvious that is wrong/torn/etc in that area.

3.8TransAM

Ok.

Couple things to check with the new info.

Do a leakdown test on the injectrors, block off the feed and return lines and see if it holds pressure after u prime it.

Ohm the injectors out, above 12ohm is serviceable most stockers should be near 16-17 ohms when all is good.

Check out the cold start injector for proper operation and function.

Get a scanner and see if your sensors all jive, especially the coolant temp sensor.

later
Jeremy

lancerus

Do I need a special tool to do the leakdown test? (I've never done that ...). Is there any rule of thumb regarding when the injectors should "just be replaced just because" ? The car has 95k miles on it, the engine was rebuilt (or long block replaced, not sure which) at about 50k. In the last 6 years the car has seen "maybe" 2k miles total.

Ohm readings I'll take this weekend.

Looking at the running readings via the MT2500 - everything "looks" reasonable. The temp sensor was failing also (reading wide open until the engine warmed up), and that was replaced after i did the MAF. (I did the MAF early feb, did the temp sensor about 3 weeks later, waited for some decent weather and clean roads to take the car out for a long haul, which was this past weekend. Note that the cold start issues went away with just the MAF change, which I found interesting since the temp sensor should have had the influence there.).

ZZ28ZZ

When the maf connector is connected, make sure none of the pins are being pushed up into the plug. I pulled my hair out for 2 weeks cause of that one.

lancerus

When I went to replace the MAF power relay - I discovered two of the wires going into the connector were messed up -- the insulation is pulled back and bare wire is visible for for about 1/4 of an inch. I was also surprised to find the connector jammed packed with grease.

Can these connectors be purchased new somewhere? Or do I need to go hunting down a used harness? My MAF connector isnt happy either - the retaining clip is broken, although the connector does stay in the MAF.

As far as the total loss of power problem - I discovered 2 spark plug wires laying on the exhaust (passenger side) - and not looking all that good. So I assume these were arching out and causing problems when the car got hot.

Red Devil

That's how most look, the grease is supposed to be there and it was more likely that your relay(s) were bad than the other MAF slowly dying. That's what typically happens anyway. Wish the search was working, there are a ton of posts on this too.

lancerus

Ok thanks. Any thoughts on where I can get new connectors that I can splice in? (since the exposed wiring cant be a good thing ...)