misfire...wont rev past 4k

[harmankardon35]

Hey

my 98 developed a pesky misfire...it revs up from idle to 3500k nicely and as soon as it hits 4000k its like it hits a rev limiter and the engine shakes. Pulled the codes...only got the obvious "misfire cylinder 1 detected"....I just got done changing the plugs and wires and the misfire is still there! Im thinking coil pack or injector. I dumped a bottle of inkector cleaner in the tank but its still misfiring. Just so Im sure...#1 cylinder is first on the front of the engine left correct? A know-it-all mechanic told me its on the back of the engine but judging from how they are labelled on the coil packs i dont think so......Any ideas? any input is appreciated!!

[LittleHoov]

as soon as it hits 4000k its like it hits a rev limiter and the engine shakes

Thats because its hitting a rev limiter. The engine WILL NOT rev higher than 4k rpms at idle in park, or in neutral below a certain speed. There is a reason for this, because free-revving the engine like that is harmful to some degree, and doing so repeatedly can cause problems. Also its there because in a no-load state like that, it doesnt take long for engines like the 3.8 to rev up too high.

Theres nothing wrong with the car, its just doing what its supposed to do.

Im not sure about the misfire code, but I would clear it, then start driving and treating the car like it should be, and then see if it comes back. If youre sitting there wrapping the engine out at 4k, youre bound to get a misfire.

[harmankardon35]

Originally Posted by LittleHoov

Thats because its hitting a rev limiter. The engine WILL NOT rev higher than 4k rpms at idle in park, or in neutral below a certain speed. There is a reason for this, because free-revving the engine like that is harmful to some degree, and doing so repeatedly can cause problems. Also its there because in a no-load state like that, it doesnt take long for engines like the 3.8 to rev up too high.

Theres nothing wrong with the car, its just doing what its supposed to do.

Im not sure about the misfire code, but I would clear it, then start driving and treating the car like it should be, and then see if it comes back. If youre sitting there wrapping the engine out at 4k, youre bound to get a misfire.

4000K? The engine should be able to climb higher than that.....Ive free revved my old beater pontiac grand prix to well over 5500k and ive driven that for years and still runs strong (i only do it because its a total beater-mobile)....The shaking is also noticable at lower rpms while climbing. Maybe im wrong and im not sure about the bigger engines, but me being a cop I am used to tromping on the v-8 crown vics (yes, in park ive tried) and being able to sweep the rpms well up into the 6-6500k range when I need to...and driving smaller cars (like my mazda mx6 v6) 4000 k seems rather low to be cutting out at. shouldnt there be another code set "speed or rev limiter reached?" Thanks for the input ill look into the rev-limiter...maybee i am just trying to rev it too high?

[LittleHoov]

Yes thats exactly my point, you are trying to rev it too high in park. The rev limiter in park is 4k rpms, which is why it wont rev higher than that.

As for the shaking at low rpms, does it do it when the engine is under a high load, for example if you are crusing down the highway and start to climb a grade without downshifting does the engine start shaking? If so its almost certainly spark plug wires.

Im not sure why you would ever NEED to rev to 6000 rpms or whatever while in park, I mean ive revved my engine just like anyone else, but I dont see the literal need for it.

[harmankardon35]

well, that was the original problem. It would ride nicely on the highway at cruising speed, but when I staerted to climb a hill or press on the gas after the rpms were @ idle coasting on the highway the engine didnt seem to want to kick up the rpms...it just kinda stayed well below 2k and the engine shook while giving it a bit of gas. Pressing on the gas harder always seemed to "downshift" out of it and it was fine...but normally the rpm's should pop right up when you hit the gas while coasting. To me it felt like transmission but I pulled the misfire code and figured that made more sence. Owning GM's for a while I had problems with the overdrive lock up in the earlier models that would cause similar symptoms (like it sticks in high gear and doesnt have power)....and when i gave it a few shots on the gas in park and noticed it topped out ~3500 k I thaught for sure that was the problem.....but now I learn theres a rev limiter so im gonna need more diagnosis. No codes in the PCM after a few good runs. I changed the front 3 spark plugs (lol, i know but i dont want to be the one changing those back ones!) and all the wires. The plugs that came out looked pretty good so i didnt bother with the back ones.

[LittleHoov]

Back ones should be pretty easy on the 3.8, Ive done an Impala and they werent too bad at all.

Take loose both of the dog bone mounts on the topside of the engine, the ones that attach to the radiator support. The engine should either freely come forward or be able to be pulled forward.

On my buddies Impala, it just kinda fell forward, and then we inched a bit more to line up with a hole that is meant to have a bolt slipped through it to hold the engine in this position. Makes doing things like spark plugs and O2 sensors much easier. It can be done on the 3.5 as well, but you have to fashion some other way of holding the engine in place.

[alejmr]

FYI I had a similar problem with my Intrigue 3.8 98 and the problem was that the cat was stucked I had to change it and the problem was solved and I mean the same problem: I could run fine until the RPM indicator reached the 3500 RPM after that no power and a misfire code appeared. The best way to test if your cat is ok: just shake it and if it rattles then you must change it if not, then go with the littlehoov advice.

[LittleHoov]

The refusal of the engine to rev past 4000 rpms is occuring in park, not while driving.

The stumbling under load at low rpm is an almost textbook example of an ignition problem, typically bad wires.

I hope Im not coming off as a jerk, just stating the facts, the cat would be a good thing to check as well, but would not typically cause the problems the original poster mentioned.

[harmankardon35]

Originally Posted by LittleHoov

The refusal of the engine to rev past 4000 rpms is occuring in park, not while driving.

The stumbling under load at low rpm is an almost textbook example of an ignition problem, typically bad wires.

I hope Im not coming off as a jerk, just stating the facts, the cat would be a good thing to check as well, but would not typically cause the problems the original poster mentioned.

no your not coming off as a jerk...

...actually I think I may have fixed the problem, Im glad i learned about the rpm limiter in park, i thaught that was a misfire lol. Thanks for the help!

[alejmr]

indeed 100% littlehoov I thought for an instant that the problem came while driving.