I have a 98 monte carlo LS 3.1L and I have been trying everything to make it run right.

I was driving down the highway last week when it started missing badly. I lowered my rpms and got off the highway, coming up to the stop sign at the end of the off ramp it stalled. It started up with alittle gas and I managed to drive home keeping the rpms low with only an occasional misfire that would jerk the car.

Once I parked at home it wouldn't stay running in idle. After cooling down it idled fine, but if i revved the rpms up it would misfire really badly at 2500-3k rpm and not climb anymore, if i floor it it dies almost but wil catch and resume idling when i let go of the pedal, or it will just constantly misfire.

If I gradually increase gas flow it will go to 3k rpm then start misfiring. If I stomp the gas it cuts out and then catches again and will misfire around 2500 rpms untill i lower the amount of gas im giving it then i can get it to 3k rpm.

I replaced the fuel filter, egr valve, spark plugs, wires, cleaned the MAF, tested fuel pressure while off and while idling and while misfiring at 3k rpms, it remained between 35-36 psi when misfiring or idling, its at 40 psi when the engine is off and 48 psi when the pump is priming. I tested the MAF voltage and its at 4.5V at idle, and it drops to 4v at about 2500 RPM. The egr valve connection to the intak is sucking air in, and the exhaust part blows air out. Unplugging the MAF or the EGR changes nothing in the symptoms.

I've posted on alot of forums, people say its the MAF or something, I think its not getting enough fuel for higher RPMS because of a slight sulphur smell while misfiring pointing towards a lean fuel mixture.

I had the coil packs and the ICM scanned at autozone and they checked out ok.

I'm really lost where to go and it's throwing no codes. HELP me please!

when testing the MAF with a DVOM what exactly am i checking for? there are 3 wires to my MAF, a yellow one on the left, a black one witha white strip in the middle, and a red one on the right. Which one do I want to check? I tried myself and one of the wires read 4.53V at idle, and dropped down steadily to 4.0V when i increased teh throttle to about 2500 RPM. I didn't test the black wire witha white line in it, the other wire read 14V so im guessing that was the power feed.

ok so I just figured out my s-10 has the same MAF sensor, So I took the sensor off my s-10, cleaned it, and put it on my monte carlo. I started it up, the injectors were pretty loud, but they usually are when I first crank it. Then I ran a bit, it misfired alittle but then it started making it to 4k rpm, and the rev limiter, So I took it on the road and punched it, it worked fine, I drove down the road with the occasional hiccup but it climbed to 6k RPM then cruised at 8- mph fine. I turned around to come back, and punched it again, and then it started missing again and I'm right back where I started. I don't know if it was working good because the engine was really cold or what, It threw no dcodes and now I'm back to where I started, I'm so confused and disapointed with the false hope I was given.

any ideas?

Ok I ran it a bit more and got the original symtoms again, except worse. I went about 4 miles to the gas station, when I pulled in, it died. I put 5 bucks in the tank then I was gonna ride softly to autozone since at lower rpms it seems to be fine, well not now. I pulled out of the gas station and it started bucking at around 1500 rpm, the tach would drop and jump all over the place. So I turned around and drove home. Even with my foot off the gas and cruising it would want to die, the tach would drop 500-600 rpm and I still couldn't get it to go over 2500 rpm, also when I pressed the gas sometimes it would seem to do nothing, Obviously this problem gets worse the more warmed up the car is, and first thing in the morning with dew on the car it managed to get to 6k rpm. I read somecodes and got a new freeze frame data from when i unplugged the MAF I think tho I may be wrong, heres the info it put out tho.

MAybe its an electrical wiring problem? I don't know.

p0102

Load 1.1%

2610 RPM

MAP sensor 37 KPA

Air Flow Rate 1.90 GR/sec

Throttle position 16.4%

Coolant temp 197 degrees.

Fuel trim same as above

Fuel system open.

If I goto I/M monitor it says OK or N/A or INC, no fails.

It threw p1676 again as well I guess I need to check that wiring as well.

Hope some of this helps, and someoen can figure out what -96.7% short term 3 fuel trim is.

I have a 98 monte carlo LS 3.1L and I have been trying everything to make it run right.

I was driving down the highway last week when it started missing badly. I lowered my rpms and got off the highway, coming up to the stop sign at the end of the off ramp it stalled. It started up with alittle gas and I managed to drive home keeping the rpms low with only an occasional misfire that would jerk the car.

Once I parked at home it wouldn't stay running in idle. After cooling down it idled fine, but if i revved the rpms up it would misfire really badly at 2500-3k rpm and not climb anymore, if i floor it it dies almost but wil catch and resume idling when i let go of the pedal, or it will just constantly misfire.

If I gradually increase gas flow it will go to 3k rpm then start misfiring. If I stomp the gas it cuts out and then catches again and will misfire around 2500 rpms untill i lower the amount of gas im giving it then i can get it to 3k rpm.

I replaced the fuel filter, egr valve, spark plugs, wires, cleaned the MAF, tested fuel pressure while off and while idling and while misfiring at 3k rpms, it remained between 35-36 psi when misfiring or idling, its at 40 psi when the engine is off and 48 psi when the pump is priming. I tested the MAF voltage and its at 4.5V at idle, and it drops to 4v at about 2500 RPM. The egr valve connection to the intak is sucking air in, and the exhaust part blows air out. Unplugging the MAF or the EGR changes nothing in the symptoms.

I've posted on alot of forums, people say its the MAF or something, I think its not getting enough fuel for higher RPMS because of a slight sulphur smell while misfiring pointing towards a lean fuel mixture.

I had the coil packs and the ICM scanned at autozone and they checked out ok.

I'm really lost where to go and it's throwing no codes. HELP me please!


It is possible the cat converter or exhaust is plugged...remove the upstream O2 sensor and go for a test run,,,leave the O2 hole open !

Fuel pressure should be 41-47 psi. Maybe your guage is off or maybe your fuel pressure regulator is fualty. Other than that it sounds like your fuel injectors might be gummed up or going bad. Does check engine light flash? Usually a misfire will cause the check engine light to flash and set a misfire code. Try getting a big bottle of Techron fuel system cleaner and refill the tank with Shell gas if you have it available around you. See if running that through it awhile improves it any. the only way to really check the injectors is with an injector drop test and coil test. A clogged up converter can also prevent the engine from revving as mentioned.

I already removed the o2 sensor and ran it, It ran exactly the same, except alot louder. fuel pressure is 41-47 psi with the engine off, the fuel regulator brings the fuel pressure down while its running, it i ungplug the fuel regulator its about 47 psi.

Ok the egr system is fixed, I ran a test drive and the I/M monitor says EGR system OK. On my test drive I had no codes but many symptoms. I got out on the road and took off gradually like the GM OBD II drive cycle says, Got up to 55mph and put on cruise control and drove 4 miles or so at 58 mph. I then gradually decellerated down to 20 mph, turned around and this time applied about 3/4 throttle and it was misfiring badly in the 2.5k-3k range, never got higher than that. I then got up to 55mph and re-equipped cruise control, it went a little bit, then it bucked alittle bit, kicking cruise control off. I traveled back to my house then cruised down to a stop at my driveway. It bucked a few more times on the way in.

I noticed that went it bucks the tachometer goes from liek 2.5k rpm down to 2k then flucuates some more before the car stops bucking and missing and settles down to slowly resume acceleration again. any of these driving symtpoms help anyone diagnosing the source of my problems?

So you're not getting a misfire code or any other codes now? Like I said it sounds like a fuel deliver problem or maybe your transmission is shuddering. Does it miss if you place it in third gear?

So you're not getting a misfire code or any other codes now? Like I said it sounds like a fuel deliver problem or maybe your transmission is shuddering. Does it miss if you place it in third gear?

this is begining to look like a cracked upper intake manifold..