Miss like it hits a brick wall at 4000 RPM

[slick94prix]

Lately, whenever I get on it, right as it hits 4000 rpm's, it's like it's the rev limiter. It will bounce back to about 3500-3600 rpm, and bounce back and forth until I let off. Otherwise, the vehicle drives fine. Idle's fairly smoothly, all gaskets are fine. Wires and plugs are perfect. ICM and Coils are fairly new, but they could be going out. The ICM and Coils are from a 99+ 3400, they were supposedly brand new, off of ebay.

Any suggestions, maybe try a new set of coils and icm? Anything else I should check?

Also, fuel is fine. Fuel pressure is fine, injectors are cool.

[Fierobsessed]

RE: Miss like it hits a brick wall at 4000 RPM

I think this ones easy. Your park neutral switch is either shot or out of adjustment. Ever rev the car when its in neutral or park? It only goes to 4000 RPM's.
Also, check the Shift cable, make sure that its properly adjusted so that when the transmission's detent is in park, that your shifters detent is also in park. Then check the switch. Another quick thing to try is to put it into drive (or 2 or 1 doesnt matter really) instead of OD, and see if that makes a difference, If it does, then you KNOW that the switch is just out of adjustment.

If thats not the problem Id be very suprised.

[slick94prix]

Re: RE: Miss like it hits a brick wall at 4000 RPM

I think this ones easy. Your park neutral switch is either shot or out of adjustment. Ever rev the car when its in neutral or park? It only goes to 4000 RPM's.
Also, check the Shift cable, make sure that its properly adjusted so that when the transmission's detent is in park, that your shifters detent is also in park. Then check the switch. Another quick thing to try is to put it into drive (or 2 or 1 doesnt matter really) instead of OD, and see if that makes a difference, If it does, then you KNOW that the switch is just out of adjustment.

If thats not the problem Id be very suprised.

So put it in 2 or D and give er hell? I'll see what I come up with.

[slick94prix]

Welp, in any drive gear, the vehicle only rev's to 4k still. But, i put it in neutral and it will rev perfect after 4k, so I am assuming its the neutral park switch. Where is it located at?

[spacecadetz26]

on the top of the transmission probably the brake booster area.

[slick94prix]

Changed it, but still no difference in the rpm brick wall.

Somebody was saying something about the VSS, but I'm not too sure about that. I might try a set of coils and icm, see what that does.

[Fierobsessed]

Do you have access to a scantool? Check to see if it's registering speed when you move and I think It will also relay weather the car is in neutral/park or any other gear. But from what I remember about the 3.4 DOHC's computer system, its the VSS that telles the computer, that tells the guage how fast the car is going. So if the speedo works, your entire vehicle speed system is working. Im not sure if the 91-93 LQ1's were the type that wouldn't let the RPM's above 4000 without the car moving. I know some cars nowdays do that.

I think your best bet at this point is the scantool. It will tell you exactly what the computer thinks and sees about what the car should be doing.

[slick94prix]

Do you have access to a scantool? Check to see if it's registering speed when you move and I think It will also relay weather the car is in neutral/park or any other gear. But from what I remember about the 3.4 DOHC's computer system, its the VSS that telles the computer, that tells the guage how fast the car is going. So if the speedo works, your entire vehicle speed system is working. Im not sure if the 91-93 LQ1's were the type that wouldn't let the RPM's above 4000 without the car moving. I know some cars nowdays do that.

I think your best bet at this point is the scantool. It will tell you exactly what the computer thinks and sees about what the car should be doing.

Thing is, the ALDL connector doesn't work, same with the SES light. I am probably throwing a code or two, but no way for me to tell.

[Lyle's GTP]

I think it's because you have a code. I noticed when I had a check engine light on my car would not allow me to do crazy things. Like punch the gas and drop a gear and rev like hell. I never checked where the RPM limiter was set though. But I think it is a "limp mode" that GM put in. I have a 94' GTP as well so check it out.

Lyle

[slick94prix]

I think it's because you have a code. I noticed when I had a check engine light on my car would not allow me to do crazy things. Like punch the gas and drop a gear and rev like hell. I never checked where the RPM limiter was set though. But I think it is a "limp mode" that GM put in. I have a 94' GTP as well so check it out.

Lyle

My car is a 93' Z34. Check the sig.

[ladyblue]

I have a similar problem that I can't seem to get correctly diagnosed.
94K miles, runs like a bat out of hell when cold (the first 5 mts or so) then once engine gets warmed up a bit, when I nail it, the RPM's jump, it bucks, hits again, steadily gains RPM's, just hesitates, catches, hesitates, catches.
gas mileage suffering dearly, from 450 tank down to 250. First time I took it in, the codes pulled were Cam position sensor and P/N switch. Thought, hey, the cam position sensor makes sense, replaced it, still does it. Runs fine until you put your foot in it. Idles fairly smooth, has a distinct rhythm, not really a miss, just a little hiccup, does it all the time at idle though. I just took it to another dealer, they don't have a clue! Told me timing chain (ha!)was bad and they won't touch my 3.4 with a 10 ft pole! I am back to believing the P/N switch has been the problem all along. Any thoughts?

[ladyblue]

BTW, after you hit it hard, the Service Engine Soon light comes in yet they swear it's not storing any codes

[patgizz]

btw holy crap old post, the car that had the problem had a bad park/neutral switch causing ECM to keep the park rev limiter even when in gear, and slick had since sold it to me, then i junked it.