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Tech Area => General Buick Tech => Topic started by: Gerry17 on July 20 2020, 07:59:58 AM

Title: engine only runs with MAF disconnected
Post by: Gerry17 on July 20 2020, 07:59:58 AM
hello everyone im hoping someone can help me diagnose my issue. MY car will not run with the MAF connected. new LT1 maf and translator, ecm, air temp sensor, ignition module and coil. tested my grounds at the ecm and all ok. checked for vacuum leaks nothing found. BLM at 128 fuel pressure holding steady at 40 psi. it will load up and stall as soon as I connect the maf sensor..load tested the maf circuits and all passed. any help will be appreciated.
Title: Re: engine only runs with MAF disconnected
Post by: Steve Wood on July 20 2020, 10:41:28 AM
that one is a new one on me.

When the maf is connected and you turn the key on, what does the maf read on your scantool (don't start the engine)

After looking at that reading, crank the car and look at the maf reading again with the engine idling.  What does that read?

Also, does it throw a trouble code when it is running?
Title: Re: engine only runs with MAF disconnected
Post by: Gerry17 on July 20 2020, 10:47:14 AM
I will check at lunchtime on the readings. there aren't any codes only a 34 because of the maf being disconnected
Title: Re: engine only runs with MAF disconnected
Post by: Top Speed on July 20 2020, 11:18:20 AM
All settings correct on the translator?
Title: Re: engine only runs with MAF disconnected
Post by: Steve Wood on July 20 2020, 11:19:55 AM
also, are you using a TurboTweak chip or something else?
Title: Re: engine only runs with MAF disconnected
Post by: Gerry17 on July 20 2020, 11:24:00 AM
Yes turbo tweek chip and double checked my settings on the translator
Title: Re: engine only runs with MAF disconnected
Post by: Gerry17 on July 20 2020, 12:44:48 PM
Just checked my MAF sensor readings and it's at 3 g/s with keep and doesn't change when its running. ⁷
Title: Re: engine only runs with MAF disconnected
Post by: Gerry17 on July 20 2020, 12:59:22 PM
with key on its at 3g/s
Title: Re: engine only runs with MAF disconnected
Post by: Steve Wood on July 20 2020, 03:49:03 PM
Then there appears to be a problem with either the maf, or the translator.

It should read 5 or 6 at idle when the engine is idling.  3 is correct with key on, engine off.

You might ask Bob Bailey for an opinion on how to tell which is bad if you don't have access to another maf to try.
Title: Re: engine only runs with MAF disconnected
Post by: Gerry17 on July 20 2020, 03:53:28 PM
it was doing the same with several stock units. but I will definitely look deeper into it. Thank you
Title: Re: engine only runs with MAF disconnected
Post by: Steve Wood on July 20 2020, 05:18:21 PM
then that seems to be another problem.   Have you checked the continuity of the maf wire back to B6 on the ecm?  It would then seem to me that the maf signal is not getting to the ecm or that the ecm itself has a problem http://www.vortexbuicks-etc.com/ecmwiring.htm (http://www.vortexbuicks-etc.com/ecmwiring.htm)

I would also make sure the maf ground wire is good, but, it sounds to me like the ecm is not getting a signal...
Title: Re: engine only runs with MAF disconnected
Post by: Gerry17 on July 20 2020, 06:27:37 PM
I just checked the MAF circuits again. according to the shop manual I should have 2.50 volts at B6 terminal at the ecm key on engine off and 2.48 volts engine running. I have 5 volts at the terminal. any idea what the correct voltage should be?
Title: Re: engine only runs with MAF disconnected
Post by: Gerry17 on July 20 2020, 06:31:06 PM
I also replaced the ecm with an ac delco unit
Title: Re: engine only runs with MAF disconnected
Post by: Steve Wood on July 20 2020, 07:07:09 PM
well, heck.

The ecm connector show a yellow wire going to B6 along with the voltages, you mention.
The maf sensor page 21-2 shows it to be a gray/red wire.  Not the only discrepancy I have seen but as long as you are on B6, that should not make a difference.  I don't have a car with a maf on it so I cannot go check it.  Those voltages in the manual are not always what I have found but I cannot confirm it.
The maf ground is black/wht and the power from the fuse/key is Pink/black

I have no idea what is happening but it sure looks like it is not getting a maf signal.  When you start it up, and rev the engine, does the maf reading move off 3?

Normally, in these cases, I disconnect the ecm connector, put my meter between the correct terminal and the terminal on the maf end and see if I read 0000 ohms on my meter to demonstrate continuity.

Do the same thing between terminal c on the maf connector and the battery negative terminal to confirm the maf ground and also verify battery voltage on terminal A of the maf connector.

If all that checks out, then I ask Bob LOL.  Maybe it is just coincidence that factory mafs and the translator are both doing the same?  But I would not spend money on that bet without talking to Bob.

I was guessing it was the ecm but you have shot that guess down in all likelihood.
Title: Re: engine only runs with MAF disconnected
Post by: Gerry17 on July 20 2020, 07:17:09 PM
I tested all 3 circuits and even did a load test to eliminate and any issues. the wire at b6 is a grey/red wire and I have 5 volts at it all the time. as soon as I plug in the connector the engine starts to spudder and stall, the maf readings stay at 3 g/s.  I have been messing with this for 3 weeks and it gets expensive when you just throw parts at it lol. I appreciate your help. I think my issue is elsewhere but its affecting maf.
Title: Re: engine only runs with MAF disconnected
Post by: Steve Wood on July 20 2020, 07:50:55 PM
I am with you on buying parts.

When you plug the maf in, does it blow black smoke out the tail pipes as it would when it went rich, or does it go the opposite way, no smoke and very lean?

You checked the Translator and saw ON, ON, ON, Off

The knobs are set for the correct maf 3" Lt1 or 3.5" https://www.turbotweaksupport.com/files/translatorinstructions.pdf

 (https://www.turbotweaksupport.com/files/translatorinstructions.pdf)I think you are down to talking to Bob...he designed it, and built it...but better, he worked in the GM research group and he understands as completely as anyone how these cars work.  And, he is really a nice guy as well.  I would try him   bob@bailey-eng.com
Let us know what happens.  I'm old but I still like to learn things LOL




Title: Re: engine only runs with MAF disconnected
Post by: Gerry17 on July 20 2020, 08:34:49 PM
yes it goes rich and starts smoking.. the translator is set 3 switches up and 1 down. I will definitely reach out to Bob. Thanks
for the info. I will let you know what happens.
Title: Re: engine only runs with MAF disconnected
Post by: daveismissing on July 21 2020, 12:11:49 AM
The 2.5volts is GM telling a tech what he might measure with his voltmeter when it is really a frequency around 100-300Hz. Different voltmeters may vary a bit. If you said you plugged in a stock MAF and got the same 5V  then it looks like maybe a wiring problem the 5v MAF supply is connected to the MAF signal.
Title: Re: engine only runs with MAF disconnected
Post by: Gerry17 on July 21 2020, 06:36:11 AM
I connected a bulb between pnk/blk terminal and the ground terminal at the maf connector and the bulb was bright. I also connected the bulb between gray/ red terminal and ground and with my power probe supplied voltage  at b6 with connector off and bulb was bright. I also checked for short to power and short to ground. no problems found with any circuit. I am checking with maf disconnected and not back probing.
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