Cutting out between 3500-4300 rpm

[John Griffin]

I have a 87 GN that is acting like it is running out of fuel or hit a rev limiter anywhere between 3500-4300rpm. This is a constant problem not intermitant. No codes on the scanmaster and everything is looking to be in range... Fuel pressure is set at 43psi with vacuum off and is rising 1psi with every lb. of boost. That is untill it starts stumbling and then the boost and fuel pressure both lower. I have ohmed the coil and they are all reading mid-12s. Spark plugs look really good and are gapped @ .32... I have checked my grounds and do not see anything that is loose

I replaced my head gaskets a couple months ago, while I did this I also replaced the injectors and got a new 5.7 TT chip, removed my EGR, installed a intake power plate, and replaced my stock MAF with a LT1 and translator.

I did look at other threads to try to find out more info but havent seen any solutions. Any help would be great!

 

[whitehot1]

How old is the ignition module ?

Autozone can test it for you but you will have to remove the coil pack for them to do it. The other big chain auto parts stores may be able to do the test also.
If you decide to do this it would be a good idea to call first to see if their equipment is working. No matter which store you decide to take it to,so you don't make a wasted trip.

 

[GNRick]

I had a stumble at 35-45 mph. Not sure what the rpm's were. If I accelerated the car picked up find. A new crank sensor fixed it.

 

[SHADOWII]

A bad/worn tps will do the same thing.

 

[John Griffin]

Sorry for the delayed response... (Family emergency) Anyway, I just got done testing the ignition module, not sure how old it is but it tested good. Also the tps is reading good on the scanmaster.

I was kinda vague earlier and this is happening when i am excelerating and it does not have to be at WOT.

 

[larrym]

What are you 02s when it stumbles?

 

[John Griffin]

I have only checked the o2 at WOT when it stumbles/misses... it is running around 780

 

[larrym]

I have had my car stubble from being rich if you do pull some fuel do it little bits at a time and watch for knock.

 

[John Griffin]

I have had my car stubble from being rich if you do pull some fuel do it little bits at a time and watch for knock.

Its worth a shot... when I get home tonight I will start trying that. Also going to try to put it under a load sitting in the garage and see if I cant see any arch coming from somewhere

 

[Heskahoka]

I had something similar when I changed my injectors. I went through a lot of diagnosis and went through a lot of different parts till I figured out that it was one out of the 6 new spark plugs I changed at the same time.

Good luck with your issue.

 

[John Griffin]

Well I guess I will replace spark plugs and wires.... I will post my findings after changing them

 

[dynoman]

When you replace the plugs tighten up the gap a little. ......028" - .030". I had a wrong plug out of a box of 6 back in 87 that caused a similar problem.

 

[John Griffin]

Replaced the plugs and wires.... No change. Is it possible I got a bad MAF or translator? I think my next step will be to buy a cheapy from the parts store and see if that makes a difference

 

[GNRick]

Hint hint...replace the crank sensor. If that doesn't fix it then it never hurts to carry a spare.

 

[GNRick]

20% off at Advance online. Use code G52.

 

[DavidM]

20% off at Advance online. Use code G52.

TRT30 gives you 30%

 

[GNRick]

Nice!

 

[MDavis]

If you have a powerlogger check to see if it happens at the same rpm. May be a wiped cam?

 

[GNRick]

TRT41 gives you 40%

 

[John Griffin]

Its not doing it at the same rpm, and when the car shifts to 2nd it will continue to miss (about 3000rpm) I will try a crank sensor... Will try about anything at this point