car stumbles at higher rpm???
 

I have an 88 Iroc with a 305tpi. The car idles and runs fine at lower rpm. When I hammer down it pulls hard to about 3000 and then starts bogging. At first I thought it was because it was in dyer need of a tune up. But I just got done installing a MSD cap, rotor, 8.5mm wires, and plugs. It doesn't bogg as bad as before, but its still pretty bad. Also there is NO check engine light on. I'd imagine its a bad sensor or something, but I'm not sure. Any ideas?

Re: car stumbles at higher rpm???
 

Check your fuel pressure

Re: car stumbles at higher rpm???
 

I'll check the fuel pressure, but I just put a new pump in back in December and have probably only put around 100miles on it.

Re: car stumbles at higher rpm???
 

Have you ever used seafoam? Ever change the filter?

Re: car stumbles at higher rpm???
 

Check your timing. Just had my Camaro on a dyno for some testing after it not shifting right, and bogging down around 3,000 or so RPMs. Was told it was not a tranny problem, but all the sensors were good, fuel pressure good, etc. Never thought to check the timing. First pull on the dyno showed .... ready ... 63, yes SIXTY THREE hp. So they checked the timing, and I forget what they said it was, but they fixed the timing, and now I'm getting a whole 178hp, with no shifting problems anymore. They said the thing runs great, I havent picked it up yet.

Re: car stumbles at higher rpm???
 

I'll check that first thing tomorrow since its shifting funny too.
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Yeah, I seafoamed it less than a year ago and the filter was done less than 500miles ago, but I have a new filter I'm going to put on tomorrow just to be safe.

Re: car stumbles at higher rpm???
 

Your running out things to change. Like :yup: , check your timing. I never thought at either.

Re: car stumbles at higher rpm???
 

Just got done checking the timing and its exactly where it should be. Also just replaced the fuel filter. Haven't checked the fuel pressure yet because I don't have a fuel gauge. Its still not running right. Its like when I hit 3500rpm the car shuts off. then its starts bogging. I'm thinking it has to be a fuel problem, because it feels like I run out of gas at higher rpm. How would I go about checking the injectors?

Re: car stumbles at higher rpm???
 

Even though your fuel pump is less than a year old, it still could be going bad.
You may be able to rent a gauge from somewhere. Years ago, one place let me buy on then return it after I was done.

Re: car stumbles at higher rpm???
 

I completeley forgot my TA has a fuel pressure gauge, so I just took it off and put it on the camaro. Its reading about 36psi at idle. Its this about normal?

Edit: Just did a search a found that it should be at about 43 with the vacumm line disconected. Which vacumm line do I disconnect? Also would an adjustable fuel pressure regualtor allow me to increase the fuel pressure, or do you think I just got a bad fuel pump?

Re: car stumbles at higher rpm???
 

Does this happen only when hot or cold, or both?

Re: car stumbles at higher rpm???
 

Its happens when both. After doing a little more searching I think it might be my Throttle valve cable. Because when I'm in first it doesnt like to shift untill about 3500rpm. and thats when I'm just driving normal. But I cant seem to find a good pic showing how to adjust it. They talk about a d-shape button or tab and I'm not seeing anything like that.

Re: car stumbles at higher rpm???
 

Wasn't the TVC, how do I know if my distributor is bad?

Re: car stumbles at higher rpm???
 

See if you can get your ignition module tested somewhere.

Re: car stumbles at higher rpm???
 

on the TV cable it will be the lower one if i rember there will be a black area that from the side looks like the letter D inside of it is a sliver area u can push to release it its been a while but u release it open the throttle then push it back in that will set the shift point

Re: car stumbles at higher rpm???
 

bad fuel injectors

i had this problem and it took me awhile to find it. tried new fuel pump, worked for alittle while then no still problem. new cap/rotor and ignition coil. solved it again for alittle while but came back

Ohm the injectors, if they dont read around 16 ohm or higher when warm, then they are bad. my car was pulling good till 4000rpms in 3rd when it started missing/stumbing, basically like a rev limit where it wouldnt pull anymore

Re: car stumbles at higher rpm???
 

I'll check that tomorrow since I just did a new distributor and MAF sensor with no luck.

Re: car stumbles at higher rpm???
 

yep i'd try that its easy to do. my car for the most part ran great in 1st and 2nd gear till you hit 3rd at about 4000-4200 rpms or so

Re: car stumbles at higher rpm???
 

Yeah, thats how mine was. It used to make it to 4000 before bogging out, but it keeps getting worst as time goes on and now it only makes it to about 3000 before bogging.

Re: car stumbles at higher rpm???
 

sounds like mine... starting getting worse as it started breakin up in second gear before i replaced them. make sure you ohm them when warm cuz i had two bad ones once warm but the one seemed to ohm ok when cold

Re: car stumbles at higher rpm???
 

Its funny that you say they didn't show they were bad till it was warm, because my car gets worst as the temp goes up. I'm pretty excited to go work on it tomorrow now. I've been puzzled for the last two weeks because I keep replacing parts with no luck. Homefully I'll have it up and runnig good tomorrow.

Re: car stumbles at higher rpm???
 

Well, got the new injectors in and had no luck. I was told to change my coolant temp. sensor because this also plays a role with telling how much fuel I need. Does this sound right? Any other ideas?

Re: car stumbles at higher rpm???
 

You didnt have to get new injectors if the old ones were good. but if injectors didnt work then maybe the temp sensor is bad..that could be another option

Re: car stumbles at higher rpm???
 

I didn't buy brand new injectors, just picked up some used ones from a boad member who knew they were all good. Gonna go pick up the coolant temp sensor today.

Re: car stumbles at higher rpm???
 

What pump did you put in? Maybe the pressure is ok but the volume isn't enough at higher RPM. The majority of higher RPM bog has been either ignition or fuel, in my experience. I have also seen the rubber hose between the fuel pump and sender tube leak or collapse, well any rubber hose collapse inside and restrict volume for that matter,and the pressure can still read good. With the fuel pressure guage connected prime it to operating pressure then see how long before the pressure bleeds off. It will give you an idea if there is a fuel leak.

Just a few thoughts, maybe this can jog someone elses memory.

Re: car stumbles at higher rpm???
 

Put the new coolant temp sensor in and got nothing.

UPDATE: Just a quick up date. The car still idles fine. When its first started and cold I can get up to about 2700rpm before it starts bogging. Once it reaches running temp, I can't even give the car any gas. everytime I even touch the peddle it boggs out. Now I have code 13, 32, and 42 showing. 13 is oxygen sensor circuit. But I just replaced the O2 sensor 3 weeks ago when I did the exhaust. 32 is for the EGR, not sure whats up with that. and 42 has something to do with timing, but I have timed it a couple time to make sure it where it suppost to be and it fine(yes I unhooked the wire by the fire wall when timing it) It also says it could be a defective ingition modual, but the distributor/modual were just replaced last week.

Now I was told if I have a bad coil, it could be burinig out the ign. modual. So I guess I should try a new coil huh?

Re: car stumbles at higher rpm???
 

maybe it could be a bad coil but doesnt really explain why you have those codes. is there any bad wiring anywhere? bad relays or burnt wires?

is it running very rich now and thats why it bogs out? could be MAF related and o2 related.. thats why i was thinking bad wiring to the o2 sensor causing a false lean condition and overly richening the mixture causin it to run bad

Re: car stumbles at higher rpm???
 

Check your dizzy shaft it could need replacing if worn. Part# 10467353.

Check and replace (if worn and showing oxydation);

Dizzyrotor #10496798.

Pickup coil #10495089.

Re: car stumbles at higher rpm???
 

hey did you ever figure out wut the problem was?? I have been having the same problem so I parked it...

Re: car stumbles at higher rpm???
 

Nope sorry, never figured it out. I did the same and just parked it. Going to look at it again when the weather warms up.

Re: car stumbles at higher rpm???
 

How is your car running? Did you get things fixed? My car is having very similar problems and I am going to begin working on it tonight. I would love to know if you were able to diagnose the problem.

Re: car stumbles at higher rpm???
 

My 87 was falling on it's face at the track last summer at about 4000 rpm... she would just trip over herself and bog, then if I let off the gas and feathered back into it she would recover (sometimes)...

She stumbled at idle too... but not all the time, some days she was fine, other days it was all stumbly...

I looked at a lot of things until I think I found the problem... my MAF is tanked... I replaced it with one from my buddies GTA and the problem went away....

Computer controlled cars... there's lots of things and combinations of things to make 'em act that way...

Re: car stumbles at higher rpm???
 

I ohm tested my injectors and found 1 to be in the extreme NO ZONE. I know you said u replaced yours but id suggest checking the ohms with a meter... mine were all 16.2-16.5 cept 1, it was at 2.5!! I replaced it and should have it fired up within a weeks time.(gonna be busy) Ill let you know!!

Re: car stumbles at higher rpm???
 

I'm having a similar problem, it'll stumble a past 3500 or so. Also occasionally dies at idle. I'm going to test my injectors as soon as I get the chance, is there any way to tes the MAF besides replacing it?

Re: car stumbles at higher rpm???
 

Well I finally got around to working on it again. I decided put a new timing chain on. When I pulled the cover, the chain had a lot of slack in it and was half a tooth off. So I finish putting the new chain on and got everything back together. Car runs pretty good now. Didn't get a chance to really get on it, but drove it arond the block a few times and everything seems good.

Re: car stumbles at higher rpm???
 

thats great to hear, sry i forgot to mention my car runs perfect now with the new injector in place... i bought a gear drive for mine so ill get to see about the slack in mine too :p