Nick-7

Lately my car has hessitated at higher rpm's, around six or so. I will be accelerating and sometimes, not all the time but most the time, the car will totally not fire a few times. It makes the car accelerate slower and is concerning me.

Last week everytime I took the car to about 4k it would act like I was hitting a rev limiter and jerk violently. I decided to replace the front coil with a spare I had lying around and it no longer acted up at 4k, but it still did it at 6k.
I have no idea what is going on. I thought it would be ignition related, but everything seems to be ok.

LongDuck

We need to know a little bit more about your car, as the symptoms for an SE that results in throttle cut out will be different than for a 12A.

Some things to think about include whether you've put any parts on it recently, or moved anything about the engine compartment. What you describe may be due to 'cross-talk' between the coil lead wires going to the distributor, as these are carrying a high voltage that can ground out to chassis and other wires if run side-by-side for long runs.

What you're describing sounds more like an ignition cutout than fuel. More info would help,

Nick-7

The car is an 84' SE. It is stock and I have not moved anything around. The only thing that I have done lately is adjust the TPS and reset the idle.

bouis

This happened to me, once, at 6k RPM or so. My car was also losing coolant. Suffice to say, I was a bit worried.

It turned out to be a damaged heater hose which would only leak under the high pressure from high rpms. This made the engine shudder. Go figure.

LongDuck

The TPS is a very finicky setting, as you're likely aware. If you've had your car for some time now, you probably realize how difficult it can be at times to adjust idle to a consistent setting, as it always seems like the ECU is trying to adjust for one thing or another resulting in an idle setting that you'd not intended.

When you stated that you've adjusted the TPS, were you using the FSM 2-light apparatus method that sets one light on and one light off? This is the required means of setting the TPS, and I can walk you through building one of these if you don't have one. Adjustment of the TPS switch outside of this device is just asking for trouble, however. The TPS works by providing a linear resistance signal to the ECU based on how far your accelerator pedal is pushed down, i.e., how far open the throttle butterfly valves are. With this signal, the ECU is able to compare against Airflow Meter signal and determine how much fuel to put in. Acceleration should be on a rich mixture, which goes slightly lean just as you push the throttle down. This is to ensure that there is enough fuel to be burned efficiently as the rpm is increasing.

The TPS being out of adjustment can cause such strange driving conditions as surging at steady speeds such as on the freeway under cruise on level ground at 55mph which will feel like the engine is attempting to stumble. This is due to the TPS telling the ECU that you're modulating the foot pedal (and Throttle Butterfly valves) and fuel is modulating up and down erratically.

When you stated that you replaced the coil and it seemed to fix the problem up to (but not beyond) 4k rpm, that may be an indication that your coil or coil wires or distributor cap and rotor are in need of replacement. Oftentimes, replacing one component that seems to fix the issue, but not entirely, is because that one part is compensating for a larger issue which is really at fault (such as wires, cap and rotor, etc.).

A good tune up will include changing cap and rotor, as these are cheap ($30) and easy to get to. Also, be sure that your wires from the coil and leading/trailing ignition are not running alongside each other in contact. If/when they cross, they should cross at right angles to one another to prevent a signal grounding out or jumping to a nearby wire or ground (chassis). Be sure that you don't have any frayed wires or worn areas on the sparkplug wires that could cause the engine to misfire.

Lastly, if you have a timing gun, time the engine and make sure that your leading/trailing timing is set correctly. As a last investigation, your high-rpm timing issue could be due to a bad or failing vacuum advance/retard which is being felt as you're accelerating. These functions are controlled by the two black and copper colored cylinders to the right of your 'rats-nest' that have vacuum tubing running through the loom, and over to the sides of the distributor. These are designed to increase ignition timing on acceleration, and delay ignition timing on coasting - all things which may be felt by your perceived 'missing' at higher rpm's.

Take a look and report back and we'll see where to go next,

GavinJuice

Longduck you always have such wonderfuly elaborate explinations

Nick-7

I did use the light bulb method to re-adjust my TPS. I just went outside to make sure that all the wire were not crossed, which some were. The rotor and distributor cap aren't too bad, I replaced them about six thousand miles ago. I have not checked the timing on the car, and I need to test the vacuum advance.
Thank you for your info

Nick-7

I had a spare rotor, distributer cap, and a set of plug wires from another 7 lying around, so I put them on. I drove the car and it seemed to do fine. I have since driven it many more times and it will do the skipping every now and then. I could not find any vacuum lines on the vacuum advance selinoids that were cracked. If this problem were consistant I could diagnose it a whole lot easier. The car will pull hard to red line in first and second one time and then the next time it my skip in first or second. It doesn't make any since.

Nick-7

I am currently tying to get the parts together to do the DLIDFS modification. I will post on my results later. I am using the GM HEI control modules.