LIM Changed, now misfires? [Archive] - Forum


View Full Version : LIM Changed, now misfires?

12-14-2004, 09:13 PM
I just had my LIM changed at my mechanic's. My wife drive's the GT, and noticed that the heater wasn't working. Checked, the coolant, it was low, checked the oil, it was orange :(

Everything's been put back together, but the car is throwing misfire codes. Is there an easy way to tell if the problem is inside with the lifters, pushrods etc. of if it's wire/plug/injector related instead? Would a compression test confirm this? If compression is good on all cylinders, then I can assume that it's something on the outside? Right now, I just want to make sure that everything inside the motor/head is good, since the outside stuff is easier, and less trouble to replace.

I'd appreciate any ideas/feedback.

Thanks in Advance!

12-15-2004, 07:20 AM
i would have him check the vacuum lines. ppl are notorious for forgeting to put these back on and it will cause a similar problem.

12-15-2004, 08:51 AM
I have noticed when doing POS LIM changes that the POS stock wires are well, POS. The metal inside comes out when taking them off. Check to see if the wires are good.

12-15-2004, 09:27 AM
Thanks, will check both of these! Is there any chance that something got screwed up inside the motor, or a way for me to find out if the problem is inside vs. outside the motor?

12-15-2004, 09:40 AM
I had the same problem. Got the LIM changed, misfired bad, no heat, car overheated, couldn't keep coolant in. It was the head gasket.

12-15-2004, 09:43 AM
Yep compression test should rule out mechanical and point you towards ignition or fuel delivery.. Did you get the codes read, and were they cylinder specific or just a severe misfire code?

And what everyone said.. triple check vacuum lines and all connectors

12-15-2004, 10:07 AM
Pulled a code saying it was cylinder 5, Would the compression test also rule out the head gasket? How can I rule out the head gasket?

At first it wouldn't hold coolant, but would a faulty cap on the coolant reservoir cause this? It seemed to hold coolant afterwards. So i'm not sure if it's an external issue (wiring, coils, spark) or something inside the motor.

Is there an easy way to get to the head gasket? Does it mean pulling the LIM gaskets again etc?

12-15-2004, 10:10 AM
I wouldn't start w/ the head gasket.. considering the heads shouldn't have come off at all for a LIM gasket change...

12-15-2004, 10:11 AM
Compression test. If the head gasket was bad, it would cause a vacuum leak, not allowing the cylinder to compress the mixture. Unless your head gasket broke where the coolant passage is, but I highly double that. A faulty cap WILL NOT cause it. Doing the head gasket means doing all the work you just did, plus pulling off a few more bolts and yanking the heads off also. Along with the exhaust (front/rear/crossover manifolds)

I would say 100% its a wiring/plug/coil issue. Yank the number 5 plug and check that, then take the plug wire and check for spark on the wire. If so, put the plug in the wire and see if you have spark from the spark plug.

12-15-2004, 10:25 AM
If the head gasket was bad, I should have had the misfire codes before doing the LIM ... right?

When we first started up the car, the temperature went pretty high, that's when we found the faulty cap (might have just been bubbles in the system)? The temperature is fine now, but it still throws the code saying that cylinder 5 is misfiring. I just want to be sure that the work done for the LIM was all okay (and didn't cause this). We put in new plugs, so it might just be a bad stock plug (Delco Platinums).

I'm hoping to rule out the head gasket, if it's something external, vaccum, injectors, etc. it shouldn't be all that bad.

Does it make sense that it can't be the head gasket if I didn't have the problem before doing the LIM (especially since the head gasket wasn't touched)?

12-15-2004, 11:52 AM
Yes, it makes sense. You wouldn't touch the heads while doing the LIM. I doubt it has anything to do with a head gasket.

12-15-2004, 04:27 PM
I was mistaken about cylinder 5, I thought it was a P0305, but it was the generic P0300. So far a compression test on the "even" front cylinders came out okay. Hopefully the 3 rear ones will be okay too (fingers crossed).

I'm hoping that checking the back cylinders turns out okay, i'll feel much better was the internals of the motor are ruled out. But even if it shows a compression problem, it could always be a lifter or something, right? (I'm really hoping it's not the head gasket!)

12-15-2004, 05:24 PM
highly doubt it would be a lifter. You dont do anything with the lifters.

12-15-2004, 06:15 PM
Argh, compression is 0 on cylinder number 5, the others all passed with flying colors. It's not low on compression, it's flat out 0. It would only do this if something's not moving, right?

12-15-2004, 06:19 PM
You probley put a pushrod back in wrong. Yank the rear valve cover off, loosen the rockers and make sure the pushrods are put in right.

12-15-2004, 06:30 PM
Thanks! Sounds like a good idea, i'm figuring if it's 0, there's something that's not moving at all. I was thinking that a lifter could have collapsed, but that's probably unlikely since all six cylinders were firing before I started this. I'll take a look at the pushrods, and hopefully it'll be something simple.