kruqnut

I have a 98 monte carlo LS 3.1L. I was driving it down the road the other day and it just started missing heavily, I lowered my rpms and got it home. When i pulled in the driveway it wouldn't stay at idle and would stall.

After it cooled off I ran it and it idled fine, but it wouldn't go over 2500 RPMS. If I pressed the gas it would just climb to 2500 RPMS and misfire constantly keeping the rpms around 2500, It would also almost stall out.

I was getting a few codes before, EGR insufficient flow popped up a few times, as well as a evap canister error code. I had them cleared and the next time EGR flow again. So I removed teh egr valve and tried to clean it up as much as possible, with the car running with the valve off of it, the intake part is sucking in air pretty good, and the other part is blowing exhaust out, I had the same symptoms (misfiring over 2.5k rpms) when the egr valve is off, I bought a new valve used anyways, same symptoms after I put it on. I also tried unplugging the MAF, same symptoms, I cleaned the MAF off as well, It seems now if I gradually press the gas I can get to 3k rpm but it starts missing then. If I press in the gas quickly it misfires alot sooner and harder.

I also tested the fuel pressure, and It seems to be within spec, 40~ psi, ~47 psi when pump is priming. ~37 psi when running, ~48 psi with the fuel regulator vacuum hose pulled off. I lose alittle pressure if I pull the throttle but it stays around ~37 psi. All this seemed normal to me but maybe I'm not getting enough gas flow? I'm working on removing my fuel filter but its corroded on there pretty good but with the fuel pressure within spec I'm not sure that would be a problem? can the pressure be good but not enough flow?

I'm stumped what could be wrong. Oh I also took the ignition coils off and the ICm and had them tested at autozone, they both seemed ok, the ICM passed the check and the coils all had 0 resistance.

This problem occurs while the engine is cold or hot, but seems to be slightly worse when the engine is warm.

PLEASE help!

Mike Sigmond

Welcome to the forum!

Id start with checking the vacuum with a guage. Its just sounds vacuum related or maybe the brake booster is going bad since you got EGR & Evap codes. I may be wrong but I am sure the members here will share thier knowledge and help you out.

MDTAHOE

You really need to get the fuel filter off (sounds like it is really old) and replace it of blow trough it to see if it is clogged. You can still have good pressure with low volume.

kruqnut

The brakes work fine except when the car is cold, they like to lockup when the car is first started, causing the abs to kick in and the traction light to show. How do i go about testing vaccuums, I'm returnign the fuel pressure kit to autozone tomorrow and I will pick up any other tools they will lend me, let me know what I need.

kruqnut

I finally got the fuel filter off, the old one was pretty grimy, thick black crap poored out of it then it went completely clogged, I put a new filter on but same symptoms.

Mike Sigmond

See if you can barrow a vacuum guage. Then look up in a manual the -pressure/vacuum it should be at.

kruqnut

i pulled a p1676 code off an OBDII scanner, any idea what this is?

I read somewhere someone mention about the brake booster, could my problems be from vacuum failure in teh brake booster? I noticed when i first started the car that my ABS would kick in when i hit the brakes coming to the end of my driveway at like 5 mph.

I jotted down some values from the freeze data, the car wasn't running when it threw the code, at least it said 0 rpms,

MAP sensor at 99 KPA

Short term fuel trim 1 0.8%
Long term fuel trim 1 0.8%
Short term fuel trim 3 -96.7% (is that normal?)
Long term fuel trim 3 8.5%

kruqnut

I had the backpressure tested and it was ok, I changed the plugs and the wires and its still acting the same.

I brought it out on the road and I noticed if I try to floor it, it will misfire immediately and not seem to even fire off anything for a second, then itll cathc and run again, if I gradually press the pedal it drives normal(but doesn't exceed 3k rpm) and will get up quickly enough and shift fine. When in O/D it starts to miss when im going about 60 mph and it's at only about 2k rpm, but itll work through that and get up to about 65 but sttarts missing mo

Mike Sigmond

P1676 is the Evap Purge drive circuit

kruqnut

Which shouldn't be what is causing this problem, as the code is pretty intermittent, I cleared it and it hasn't came back but my symptoms are exactly the same.