Running poorly over near 3000 rpm

[brota]

Sorry for repost I put it in the wrong section
Hello I have a 1995 Firebird with LT1.
A few weeks ago I was driving my car got stuck in some rain (which I didnt do often). The car started to run a little funny.
Next day it cut out when I was driving it after a few minutes I was able to restart it.
Doing some research it sounded like the opti maybe got wet. So I replaced the opti the seals and water pump.
I drove it and when it was warmed up it started to cut out when I stepped on it.
it also seems to have trouble going over 3000 rpm when the issue is happening even when rev it.
Fuel pressure looked good.
Scanned with Scan9495 and eehack no codes other than maybe some from running with sensors unplugged but clear and have not come back.
Not sure what to look for in the app besides that.


New ICM and MAF were installed
Carquest/Advanced Auto opti was installed


See the video it starts at about 11 seconds my foot is almost to the floor.

https://youtu.be/B0OLaorlV4M

Both datafiles can be opened with excel

[Stormyweather]

Opti vent hose in good shape? My hose was old it would close up on full throttle making the Opti miss fire do to the cap touching the rotor probably not your issue though.

It's not how fast you mow. It's how you mow fast.

[kitt8090]

Mine was a shit msd coil....

Sent from my Z963VL using Tapatalk

[brota]

Thank you I was able to blow air into the lines so I do not think that was it but good though!!

I ran a new scan with scan9495 I figured out my index issue was because I didn't save the file it was just the default collection file.
here is a new file incase anyone knows what to look at.

[Injuneer]

Previous thread for reference.

http://ltxtech.com/forums/showthread.php?31190-Could-this-be-a-bad-ICM&p=482355#post482355

[brota]

Link to file new scan

https://black55chevy-my.sharepoint.com/personal/brian_black55chevy_com/_layouts/15/guestaccess.aspx?docid=10d8ba4cdfb1b47a78d1025242a ae3085&authkey=AaKtz0KdL2io1-WB3mO79rQ

[brota]

The coil be the last thing I try.
I am not doing the opti again, I will sell the car first :laugh:

[GaryDoug]

Everything looks pretty normal as far as I can see. Fred is the real expert, I learned anything I know from him. But if I were you, I would try to check the fuel pressure when this happens. No codes for that.

By the way, it doesn't matter when you save the log file, either as its being logged, or after the scan is over. The files will be the same except for the name. The original file was definitely a transmission data log.

[brota]

Great thank you.
I did test fuel pressure but not sure it was when it was happening.
It was where it should be and there was no leak down.
I will try and test it again after I do the coil.

If it is the opti again it is going in storage for a bit.

[Injuneer]

Not sure how you managed to end up with 5 identical copies of the log in one file..... there is about 3 minutes of useful closed loop operation. Still need to look at it in detail, but the numbers are all over the place. At idle, the LTFT's are 160, indicating the PCM is pouring in at least 25% extra fuel to maintain the A/F ratio. High LTFT's in Cell 10 (147/149) adding extra fuel. Might tend to suspect low fuel pressure. But then there's Cell 11 at 122/122, and Cell 14 at 121/123.

But then when you open the throttle any decent amount (doesn't matter whether the car is moving/under load, or if it's just sitting still) and you're revving the engine, both O2 sensors go pig rich (900 - 1000+ mV) and stay there even after you close the throttle. If it was in PE mode, that might make sense, but most of the time it is in PE mode for only a fraction of a second.

Never saw anything like this one before.... but give me some more time to try and figure out why it's so screwed up.

Have you pulled any spark plugs to check condition?

Check the fuel pressure anyway, and respond with numbers. At idle, vacuum comp line attached; at idle, vacuum comp line disconnected/plugged; out on the road under load, as high an RPM as you can reach. Check for wet fuel in the vacuum line. Pull the EVAP line off the throttle body and see if there is any wet fuel in that.

[brota]

I may have just kept hitting save :laugh:

I have the new coil to put in.
I will try and test the fuel pressure again.
I do have a gas small once and while.

I really appreciate you looking at this.

[Injuneer]

Also check your oil for the smell of gasoline.

[Injuneer]

OK.... may have found the problem. The MAF will suddenly go from a seemingly normal reading of 50 grams/second or less (around 2,000 RPM, 35% throttle), to readings in the range of 197-199 grams/second. That drives the injector pulse width to numbers like 30-40 mSec. Since the signal from the MAF sensor is frequency based (Hz), could be some sort of high voltage interference at the sensor or the signal wire from the sensor. Or maybe a faulty MAF.

Do you have access to a temporary replacement?

[brota]

Yes I just replaced the MAF so I have the old one. Or I can grab a new one from advanced.

Yes I do have gas in the oil (i think) It was overfull so looks like I will be draining soon.

Tested the FP again
41-44 Key on
36 running 42 when vacuum line unplugged.
Didnt see any gas at regulator not sure if i took the correct line off evap but didnt see any gas

When running it never seemed to dropped below 34 even when hesitating

Should I also try running with MAF unplugged?

[Injuneer]

Drop all the fuel pressure stuff. We figured out why it's running poorly.... MAF is causing it to pour tons of fuel in when the reading goes sky high. That's what diluted the oil. You will probably find badly fouled spark plugs.

Running with the MAF sensor unplugged will not tell you whether it's a faulty sensor or some sort if interference with wires. But the engine should run better, so that would confirm it's an MAF "SYSTEM" problem. Unless of course the plugs are so fouled with fuel it's misfiring.

Smell the oil. If it smells like gasoline, change it immediately, or you will damage the bearings.

[Puck]

Drop all the fuel pressure stuff. We figured out why it's running poorly.... MAF is causing it to pour tons of fuel in when the reading goes sky high. That's what diluted the oil. You will probably find badly fouled spark plugs.

Running with the MAF sensor unplugged will not tell you whether it's a faulty sensor or some sort if interference with wires. But the engine should run better, so that would confirm it's an MAF "SYSTEM" problem. Unless of course the plugs are so fouled with fuel it's misfiring.

Smell the oil. If it smells like gasoline, change it immediately, or you will damage the bearings.

This is very important. I had an EEPROM go bad and cause my tune to dump tons of fuel into the motor. Swapped the chip and got it running within a few days, but didnt change oil quickly enough and car developed a low hot idle oil pressure issue due to gasoline diluted oil.

[brota]

OMG thank you so much!!!
I just changed the oil and put my old maf back in. I changed it a couple months ago because i had a brief hesitation. I didn't seem to have it tonight.
Now for my mental state I hope I really did need my opti replaced. I think the water pump was steaming a little and the seals seemed to needed to be done so it couldn't be all bad.
The car seemed to be running on all 8.

Is there any training out there on understanding the values from scantool?

Thank you again everyone who contributed.

[Injuneer]

I have a guide that may help you a bit. I'll try and upload it tomorrow.

[Injuneer]

See attached.

[brota]

Fantastic thank you

[Injuneer]

brota Is it still running OK with the "old" MAF? What brand was the newer replacement that seems to have been the source of the problem?

[brota]

I have not driven it much besides the test ride maybe try to take it out today.
It was a spectra from Advanced Auto. Based on the other night it seemed to be the issue.
It is rainy out today so it may be a good day to test the overall car.

Thanks for checking in.