Upper RPM skip

9 Deuce GT · Jan 13, 2008

A few years ago I installed some performance parts on my '92 GT. It runs great, and has the power I was looking for, but it seems to have develpoed a slight issue. I rarely push the car hard, but every now and then I like to take it up a little past 5,000 rpm just to see what it's got. Well I have noticed that there seems to be a skip or sopme sort of miss when the rpm's go this high. It is fine when driven below this rpm level. My first thought is was the AFR valve springs. I unfortunaltey did not upgrade the springs when I purchased the heads. Another thought may be too much fuel. Here is a list of parts currently on the car that may help someone diagnoes this issue:

Stock 77,000 mile short block
AFR 165 pedestal monut heads
FRPP 1.6 rr
TFS Stage 1 cam
Tmoss ported Cobra intake
PMAS 80mm MAF
FRPP 65mm TB
FRPP 30 # injectors
Kirban AFPR
FRPP 190 lph pump

The oldest upgraded part has around 4500 miles on it, and that would be the heads and intake. I know the injectors are too big for this combo, and I may switch back to 24#'ers soon. Could too much fuel cause this issue? Can I tell by pulling the plugs and inspecting? Let's say the valve springs were the correct pressure for this cam, could an incorrect size push rod cause this? I had a bitch of a time shimming these things, (Why did I not get stud mount heads?????)!

If anyone can help, it would be appreciated.

dcurtis · Jan 13, 2008

Don't know whats wrong with it but I bet the afr springs are fine for that size of a cam.

jhonda · Jan 13, 2008

you may want to upgrade your ignition

jrichker · Jan 14, 2008

A high RPM miss on a warm engine is a sign of a TFI module going bad. You can have it tested at most auto parts stores, but you will need hair dryer to heat it up and get it hot. They only fail when heated when you run them on the bench tester.

9 Deuce GT · Jan 14, 2008

Just a quick thought:

A bad TFI module can cause a non-start situation on one start-up, but then act fine any other time, can't it?

I have had a few instances where the car would act dead when the key was turned, like the battery was dead. But when driven others times, it would start up fine. I have had the wire on the starter get corrosion on it before to where it needed to be replaced, and I really thought this was the same deal. But maybe not.

BK_CAULEY · Jan 14, 2008

the cutting out could be numorus things. have you checked your plugs to make sure there not fowled? checked your rotor and cap for corrosion? made sure all of your spark plug wires are ok?
im pretty sure it is, but is the MAF calibrated for the injectors? i doubt its getting to much fuel. the ECM should detect that and decrease fuel if o2 sensors are working right.

and as for the TFI question as long as its cold starting the TFI module shouldnt affect start up. it will only affect the running condition after its been heated. if you are having trouble with random mis-starts i would check the starter solenoid, but first check all of the battery and cable connections (+&-) to make sure you have a good clean and tight connection.

jhonda · Jan 14, 2008

I just put a ignition control module(TFI) on my car. I noticed bad gas mileage, lack of power especially when up to temp. Only way to compare the power loss is like going from 3.73gears to 3.08s. The module only cost 39 dollors with tax, so I tried it and it worked. if you take it off to test it and your car has any miles on it you might as well replace it. On mine and I think all the V-8s you have to pull the distributor on the 4 cylenders you can leave it on. I had to make a special socket to get it to fit in the mounting holes, I think it was a 11/32 size but I had to grind the edges of the socket down to get it to go deep enough to grab the bolt head.

DKVL · Jan 5, 2009

I think i am experiencing this. I noticed that when i am in 4th gear and high reving (4500+ RPM) my car seem to miss (or at least sound like little marbles bouncing around faintly). In addition, when my car is warm or driven for a while, I would shut off the engine for a quick starbucks. Then when I want to start the car again, it takes a long crank or two cranks to start.

I am assuming the TFI is the issue, but what is a TFI? Where is it located and how much is it?

Is it really called the ignition control module? What does it do?

How do i figure it out for sure.

Upper RPM skip

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Upper RPM skip

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