Kevin Michael

Got a pic of that Maf and what you paid? Sounds interesting.
Kevin

Tampa 928s

It's in the car now and I don't want to take it out and have bad mojo. It just has two tiny holes with adj screws. I'm not sure this was a part of the Maf rebuild adventure. He did this for me trying to dial in this S/C nothing else worked to get the A/F correct. I'm sure he could make you one, I would say you could rebuild yours and have him add this to it.

Fabio421

Mark,

Whats the final verdict. Have you logged a run to see what your A/F is under load and boost?

Tim Murphy

I think you still may have an issue going on that is going to haunt you until you find it.

This is a snip from the latest data log you sent to me. See where the injector duty cycle spikes up for no reason, causing the maf to instantly go rich? This is due to some sort of electrical issue and you need to find what is causing it. I've seen this happening in just about every data log you have sent. It is easiest to recognize during idle or cruising with a steady throttle.
You can connect your laptop and run Logworks realtime and I'm sure every time you feel a stumble or stutter you will be able to look at the graph and you will see the blip on the injector duty cycle.

Causes....? Possible short to ground in the injector wire harness or possibly a bad LH are my guess.

Tampa 928s

Tim,
I have not posted a current log this is a run up the street just a quick drive and forgot to record the Wot run. The car ran great except when I restarted it the super charger was making a noise and I noticed a little oil on top on it. I have restarted it and now its back to normal.

Fabio421

Too lean man. Fatten that thing up to 12,5 like we talked about yesterday. Of course I fully expect you to ask Tim first but you are running without knock sensors or an intercooler. 12.5 is safer.

AO

I don't know if anyone else saw this, but it looks like there is still an issue even under cruise.

Tim Murphy

I have another customer who recently had a shop in Texas install a Stage 3 kit on an 87 S4 AT and he was having all kinds of intermittent running problems. We kept thinking it was the MAF and swapped it out a bunch of times. Every time we changed the MAF it would seem to run fine, for a while, then would go back to having problems again. Well, after lots of diagnosing the shop found the problem......AND...... it turned out to be the voltage regulator on the newly rebuilt alternator.

Mark, it would be nice to data log the voltage that feeds the LH computer to see if something might be going on there. The data log you posted is showing some spikes, as Andrew pointed out, that should not be there.

Z

You're realy not doing yourself any favors with that custom tunable MAF. By using it you're tuning around the problem with extreme settings instead of fixing the problem. Your problem is intermittent. You have times when the engine is running excessivly rich. If you tune it for a correct air/fuel ratio when the excessively rich condition is occurring, what do you think is going to happen when the the underlying condition causes things to go back to the way that they're really supposed to be? What's going to happen is that the mixture will be too lean then.

Based on the information you've provided so far, it really looks like you have a voltage problem. If the LH computer isn't getting a high enough voltage, it will increase the injector pulse width to compensate for the slower opening time of the injectors at lower than normal voltage.I don't know exactly what the minimum voltage required is, but have seen weird intermittent running problems when the LH computer was only getting 12.2-12.5 volts or so. I'd say that if you aren't getting over 13v, find out why. If you've checked the ground and battery conections mentioned before, the alternator is a real possibility. It could be a bad alternator, or maybe just a bad connection at the alternator.

If you remove the cover off of the LH connector you can access the terminals from the back with it connected to the LH computer. You can then measure the voltage between terminals #9 and #5. If you want to log that voltage with the LMA-3, you'll need to make a voltage divider to reduce the voltage by about 1/3, since the LMA-3 can only measure up to 5 volts.

Tim Murphy

I talked to Tampa earlier today and it is possible he found the problem.

As far as the statement above goes.... if you have oil leaking from the supercharger then that would be a warranty issue with Vortech and we can address that accordingly. I'm not quite sure why you threw that out here in this thread but, perhaps,........hmmm?

For those following this thread, Tampa tried a different LH and all his symptoms are currently resolved. The data file he sent to me does not show any of the injector duty cycle blips as AO, Z, and I have previously pointed out. Tampa is going to try some more tests to verify that the problems were from a faulty LH and I'm sure he will chime in with the good, or bad, when he gets the data. For the moment, it appears to all be working as we hoped it would.

Tampa 928s

I THOUGHT I WOULD GIVE AN UPDATE ON MY SAGA OF THE ELUSIVE SKIP.

I had the fun of replacing my comp flap this weekend, found a torn elbow for the main vacuum to the solenoid assembly and adjusted my recirculation valve. The air is now back and working good.

While everything was apart I decided to check on my electrical connections on the CE panel. On the top is two large gage wires with nuts attaching them. I removed and cleaned them after removing the plastic shield. What I did find was that three of six power wires that go to the relays including the injector relay were very loose. I could not pull them off but they would wiggle back and forth a lot. I opened up the spade connector and re-crimped them and replaced one that was not salvageable. I did a 40 mile run today and not one skip or drop out, with the cool air on of course. I hope and pray this is it. I have been chasing this for a long time now, just thought you would like to know.
Mark

AO

Good job! Gremlins suck.

Tim Murphy

Wel, all along we suspected something electrical. Good job sticking with it and finding the problem.

If all keeps running well, it's time to turn up the boost on that bad boy!!