Misfire problems, Loss of power.
 

Hi I'm here to ask for help. If these forums are anything like thirdgen I'll be over the moon. My girlfriends 99 Montero has given her about a million problems over the past few months.

Currently it makes a backfire sound and eventually loses acceleration. She'll drive normally and all of a sudden it does this. In the past month the fuel pump has been replaced and also the crank sensor. Also apparently her cpu as well

There is an error code but I haven't been able to check it yet, she keeps taking it to a tuffy and I feel like they've been ripping her off and making up reasons, or are potentially just idiots. I come to you all for help. Thirdgen has never wronged me and I'm sure y'all won't either. Just looking for some ideas of what it could be.

Spark plugs? vac leak? I'll find the code tomorrow hopefully

Post the code. It will help to narrow it down. It can be no spark, an unbalanced air/fuel ratio or a bad fuel injector. Once you know the code you should be able to tell if it happens to one cylinder only (than spark plug or fuel injector), or to all - air fuel mixture control.

Cylinder1 misfire. Supposedly tuffy already diagnosed this and everything checked out fine. I tend to not believe that at all. They came up with the idea that the cpu was defective and replaced it with a used one. Is it possible that this cpu could be faulty as well?

Also, she's younger and lives with her family. Her dad doesn't like the idea of someone who's job isn't to work on cars to work on it. If the car's just going to sit there though I feel like something has to be done. Where would be the easiest way to start? Check the plugs? And when people say it's apain to change them out, what are we talking,like an hour? Two?

P0301

Hey Alex I bought my 98 Montero 3.5l sohc a few weeks ago and had the P0301 come on as well. I would clear the code, but it usually came back on when I put a heavy load on the engine. I thought the sluggish acceleration was because of the weight, but I just finished replacing my spark plugs and ignition wires yesterday and the car runs MUCH better now. I think that replacing the plugs/wires might solve your issues and especially if they've never been replaced before. It is a bit time consuming if you DIY, but just take your time and it will be worth it in the end. I used the following awesome guide:

Montero Sport Online » DIY – replace spark plug

I think changing a CPU on a misfire code is excessive, unless every other possible thing is checks out. The fact that swapping CPU did not help leads me to believe that there is another culprit and the previous work was for naught. Couple possibilities - bad spark plug, bad spark plug wire. Google the nominal resistance value on the plug wires for your year Montero and check to see if the actual measurement is within specs. You can always replace all spark plugs and wires (do you know how long ago that work was done?). Quesiton:
Does '98 Montero have a single ignition coil with a distributor or a set of 3 mini coils? If it is distributor, than you may have a problem in there (crack, corrosion, etc). It if is 3 separate coils, than if one fails, you should be getting two cylinders misfiring.

how long total do you think it took you to change them out? Couple of hours?

I estimate it took about 3-4 hours of actual time if we didn't run into any problems. My friend helped me out so we just took our time and worked on it over a span of 2 evenings. It would have taken 1 evening, but a heater hose leading to the throttle body cracked (due to age) while moving the plenum so had to wait until the parts store opened the next day. We also had some trouble reinstalling the 2 EGR tube bolts due to the tight space so that took some time.

Spark plug for cylinder 1 was changed out. Helped for a little while, but the car won't get above 1000 rpms. There is little to no power and the error code is gone. A family friend is working on the car as we speak and is going to change out the other plugs. He also thinks the MAF is bad. Is it possible that it could go bad and not send an error code?

Double post