Lt1 Maf On V6

[BOOSTED]

Tuning 2001 Monte Carlo, 3800. Intercooled turbo kit, came with LT1 MAF,43lbs injectors. tuned first VE, then connected MAF, then tuned MAF by % error, car runs great until after a few restarts after sitting or coming to a stop after a few drives a p0300 code shows and rough idle starts and scanner shows misfires in 5 of the cyls. If I disconnect the MAF no misfires, tried another LT1 MAF misfires come back. This only happens at idle. Do I need to work in MAF delta airflow area?...or somewhere else?

[Eddie-98GTP]

Does the MAF sensor have a screen? Removing this can cause all kinds of drivability problems. Also, is it before or after the turbo?

Another question - how are your fuel trims? Is the engine running too rich (very low LTFT) or too lean (very high LTFT)?

Be sure there are no vacuum leaks. A leak after the sensor will cause the PCM to try to correct for something it can't see. Disabling the MAF will remove this as a calculation and could mask a vacuum leak.

I'm running an LQ4 MAF (pretty much the same thing as an LS1), and have never had any problems.

[z34phoenix]

i would also work check for vac leaks and watch the fuel trims... i have a maf similar to what you guys are runing that is stock on the DOHC motor. i have heard drivablitiy and tuning issues as well without a screen, but i do not run a screen myself.

i did some porting to my stock TB and increased the flow... so i wasnt able to put the screen back in cause it wouldnt fit. i have not issues because of it. when the car was stock, i would get a SES light when i didnt ahve the screen and it would only trigger at WOT

[JerryH]

P0300 is misfires. I bet you have an issue with one or more of the following:

- one ore more bad spark plugs
- one ore more bad or loose spark plug wires
- corrosion on one ore more of the coils
- defective coil(s)
- corrosion under the ICM
- bad ICM

Don't bother doing more tuning for the moment until you fix this hardware issue.

<soup nazi mode>
No more tuning for you!
</soup nazi mode>
(lol)

(edited for typos... again)

[John_F]

Post up your tune. It has to be in the tune somewhere if it runs fine to start with and then after a few driving cycles it starts misfiring again.

[JerryH]

I am willing to bet its not in the tune. If he is setting a P0300, thats a misfire (the car is already telling you where and what the issue is!). Misfires are an indication of hardware issues. A v6 running on 4-5 cylinders is not going to be too smooth.

Can the HPT scan individual cylinders for misfires? If so it will tell you right away where to look.

[John_F]

If I disconnect the MAF no misfires

OP's quote ^^^

[John_F]

I'm going to get back to GTO tuning now, let you guys handle this stuff.

[JerryH]

If he disconnects the MAF, a lot changes. I still would check for the obvious. When I disconnect the MAF, my car doesn't get P0300 codes and no turbo or supercharged car I have ever tuned did either.

Start with the obvious/easy and work from there. I never advise fixing a harware issue via tuning.

[devildog9999]

How much was the MAF scaled? 85mm Maf and what size intake?

[BOOSTED]

Thanks for the recommendations, the screen is in the maf, all new plugs,wires. Checked for vac leaks, found a small one, fixed it, checked grounds none bad. If the maf is disconnected car runs and idles fine, every cyl except number 5 had multiple misfires with the connected maf. We moved the injector to cyl 1 from number 5 cyl, We then had no misfires in number 1 cyl but 5 did have misfires after the injector swap, we are leaning toward some problems with injectors that we were supplied with. ltft trims 0 to 2

devildog.... the LT1 maf with screen is attached to the original maf that has no screen by rubber connector. and can you let me know what do you mean by how much was the maf scaled?

[johnh]

Hmmm... bad MAF?

Any chance you could try a replacement MAF and see if the problem occurs?

Or you could try the hammer test...this is where you tap lightly on the maf with the handle and see if there are any erratic readings....

[devildog9999]

I was thinking it may be scaled way off... seen this kind of thing before.

[Perforator]

the LT1 maf with screen is attached to the original maf that has no screen by rubber connector.

Are you saying that both MAF sensors are being used in the intake at the same time?