car running really really bad! I NEED HELP!!
Thread Starter
Joined: Mar 2003
Posts: 8,319
Likes: 1
From: North Carolina
car running really really bad! I NEED HELP!! ok my friends car runs like ****. its missing really bad under load, any kind of load. sometimes it is ok though. fuel trims were maxed out and we replaced the MAF and it ran great. then rean shitty. replaced the plugs and ran ok for a little then shitty again. now its getting a p0300 random multiple misfire. we checked all the coils and they are all sparking. replaced the o2s they are fine. got some new ngk plugs and they are fine. new fuel filter too. my only guess would be fuel pump now. its a 98 trans am with 80k miles. did a top end cleaner too....any help would be GREATLY appreciated
Thread Starter
Joined: Mar 2003
Posts: 8,319
Likes: 1
From: North Carolina
yeah wires are fine. i mean we checked it all out. pulled all the wires to check for spark and they all sparked great and im talkin about we went up and down this thing. im not sure what else it can be really, im not big time mechanic im 19 and he is 18, he knows his stuff but not too much....i know quite a bit and learned a whole lot on here but i dont knwo everything so im sure there are pleanty of other things it cna be. coils, o2's, plugs, wires everything is good, did top end cleaning, checked inside the intake for any excessive oil build up, checked the computer out and everything....i just odnt know what else to do if the fuel pump doenst do the trick...
Thread Starter
Joined: Mar 2003
Posts: 8,319
Likes: 1
From: North Carolina
i used the predator cause that was all i have. i also used the inspection machine at work to check out the idle parameters to see things. fuel trims were +25% all the time until the new MAF and then they were around 0% at part throttle driving.
Had same issue with a buddies 98' Z ended up being a broken intake pushrod on # 7. It also gave off a PO307 code #7 cyl missfire too which pin pointed the cyl to me right away. replaced the pushrod, ran great!! 2 weeks later it really started running like trash and idled fine no shaking or poping but wouldnt rev over 4K at first and then later wouldnt rev over 2500K. But the thing is the car ran beautiful just lightly driving around, it sounded like 3.1 V6 out the exhaust though. Well of coarse the putz didnt say anything to me by this point and he burned the check valve out of the driver side air injection tube and burned a hole in the hose and everything. Naturally it turns out it had a plugged up coverter on the driver side. This car had about 82K on it, this was the 3rd F body i knew of that smoked 1 or both of the cats between 75 and 90K.
Maybe food for thought it seems like it may have one of these issues i saw from what you described. It only threw a PO300 random misfire DTC at the time too.
P.S
DONT waste any more time or money replacing parts that are not needed like you have been doing!!! NEVER assume while troubleshooting something make sure its a black and white case of a failed part before you replace it.
Maybe food for thought it seems like it may have one of these issues i saw from what you described. It only threw a PO300 random misfire DTC at the time too.
P.S
DONT waste any more time or money replacing parts that are not needed like you have been doing!!! NEVER assume while troubleshooting something make sure its a black and white case of a failed part before you replace it.
Last edited by BADDLS1SS; Dec 30, 2003 at 02:45 PM.
Thread Starter
Joined: Mar 2003
Posts: 8,319
Likes: 1
From: North Carolina
well the thing is everything we did didnt cost much money most of the stuff was regualr things we were gonna do anyway but thats why i asked about the fuel pump. i was thinkin today and figured it could be a few bent pushrods. the cats arent on there. thanks for the imput we will pull the pushrods out and see...
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You can determine if the fuel pump is a problem if you gotta gauge to hook up to the shroeder valve on the fuel rail and see if its maintaining its 58 PSI consistently....
Pushrods can get bent super easy in these engines LOL, its worth a shot to pull em and roll them on a piece of glass or a mirror and see whatcha got.
Pushrods can get bent super easy in these engines LOL, its worth a shot to pull em and roll them on a piece of glass or a mirror and see whatcha got.
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Verdad Gallardo If the car was driven around with +25% LTFTs
it means it was driven around lean (25% is a
limit value, it wanted more). Gross lean can make
a lot of soot from misfires and quite possibly foul
O2 sensors. Use the Predator to look for lots of
activity at part throttle and steady, .8-.9ish
readings at WOT. If you see the O2s "stuck"
low at cruise, maybe they're fouled (which
could also be a cause of positive LTFTs,
chicken & egg).
Fuel delivery can be a cause of load problems;
filter, pump, pump wiring, kinks in the lines from
"off-roading", accumulated crud in one injector
etc. A fuel pressure gauge can tell you about
it to some extent though it's hard to make full
load in the bay. Inspect the lines, check for
cylinder-specific misfires if you have access to
something like EFILive. Injector balance test
would point out any problems like crud in isolated
injectors.
Open-air spark and idle spark don't rule out coil,
wire or plug gap problems. High cylinder pressure
(as under load) requires up to 10X more voltage,
can show a marginal coil or wire insulation problem.
it means it was driven around lean (25% is a
limit value, it wanted more). Gross lean can make
a lot of soot from misfires and quite possibly foul
O2 sensors. Use the Predator to look for lots of
activity at part throttle and steady, .8-.9ish
readings at WOT. If you see the O2s "stuck"
low at cruise, maybe they're fouled (which
could also be a cause of positive LTFTs,
chicken & egg).
Fuel delivery can be a cause of load problems;
filter, pump, pump wiring, kinks in the lines from
"off-roading", accumulated crud in one injector
etc. A fuel pressure gauge can tell you about
it to some extent though it's hard to make full
load in the bay. Inspect the lines, check for
cylinder-specific misfires if you have access to
something like EFILive. Injector balance test
would point out any problems like crud in isolated
injectors.
Open-air spark and idle spark don't rule out coil,
wire or plug gap problems. High cylinder pressure
(as under load) requires up to 10X more voltage,
can show a marginal coil or wire insulation problem.
Staging Lane
Joined: Nov 2003
Posts: 57
Likes: 0
From: Arizona
Did you recently unclip any of the pig tails to the coil from the injectors? If so, you may have bent the connectors pushing them back on. That will cause a mis-fire if enough volts are not flowing through. If you can log the mis-fire to determine the cylinder (s) misfiring then you can pull those and take a look inside the connector to inspect for damage.
TECH Enthusiast
Joined: Nov 2001
Posts: 521
Likes: 0
From: Farmingdale NJ
Possible vacuum leak somewhere? +25 is WAY lean! Also check for some type of intermittant fuel delivery problem, like a clogged filter. Put a FP gauge on there, and tape it to the windshield. It may be fine at idle but with a restriction the pressure will drop dramaticly at load. Tape the gauge to the windshileld, carefully shut the hood (so you don't pinch the hose) and go drive the car. If the pressure drops a lot under load, you have a fuel delivery problem.
Oops, just re-read the first post and I guess you did a fuel filter already. Well, do the fuel test I described anyway. It will still help you diagnose a pump or other restriction.
Oops, just re-read the first post and I guess you did a fuel filter already. Well, do the fuel test I described anyway. It will still help you diagnose a pump or other restriction.
Thread Starter
Joined: Mar 2003
Posts: 8,319
Likes: 1
From: North Carolina
yeah i was thinkin about doin that. fuel trims were fine after a new MAF, it was my old slp he bought from me so i mean we didnt just go buy a new one for it....but ill try that one too, thanks
