I am having this recurrent problem with my Superchip. I get a high rpm miss which at times is worse then others. This weekend I towed my 5th wheel trailer (small 18.5 ft) to Florida. I was able to do 70 to 80 consistently on the expressway but sometimes the transmission would down shift to third on inclines (with the 4:30 gears and Transgo kit I tow in OD). At that time the engine would miss bad as though it were firing against the compression stroke.
This happened once before when I put in the 4:30 gears. At that time the plugs were gapped too much and re-gapping the plugs and installing the proper transmission gear corrected it.
This time the plug gap is fine and the gear has not changed.
When I removed the Superchip this stopped happening.
The only thing I can figure this is a result of the advanced timing of the Superchip, especially at high rpm. Also with the Superchip I have been getting a flat spot in the acceleration. This is gone when removed and it seems to pull hard all the way thru the rpm range.
Any ideas mike??

 

Hi WLF,

My first reaction is that you'll need to look elsewhere, as it is not the Superchip causing the engine to miss if it is properly installed, and I'm sure it's installed just fine, I don't think that is the problem at all. The Superchip is basically an all or nothing type of device, it cannot cause an intermittant high-rpm high load miss like that, or any other kind of ignition miss.

All the Superchip does is retune the engine for the use of premium gasoline. It doesn't do anything to your ignition, it cannot cause your engine to misfire if it is properly installed and the code matches, and it cannot cause your fuel system to have problems, nor can it cause anything else to have problems.

Sounds like it's time to go thru this vehicle thoroughly, since it's a 1997 model, and get all it's maint. done properly, starting with the entire ignition system & fuel pump & fuel filter, too. You should be able to turn 5000 rpm with no misses even in high humidity with a plug gap of .050, and if you can't, it's time to upgrade the ignition.

It's obvious your engine is misfiring under load, and that clearly points to an ignition problem (assuming we don't have an obvious fuel delivery issue such as a worn out fuel pump or a clogged fuel filter, or water in with the gas), which is the same problem you had before. Apparently you helped to temporarily bandaid it by regapping the spark plugs, but that didn't solve the actual underlying problem.

Give us a call to go over this, so we can spend some time with you, is my best suggestion. I will be out of the office tomorrow & probably part of Wednesday, but if you'd like to give us a call say, Thursday or Friday, I can spend some time with you going over this in detail, & let's see if we can get this figured out!

 

I will call you.
Prior to the last time this happened I had larger tires without a corrected speedometer. This had my timing somewhat retarded so with the Jacobs ignition, I was able to run gaps in excess of .070. As soon as I changed the rear, I went to the other end of the spectrum with the Speedo reading much higher then actual speed and thus advancing the timing. That is when I got the same kind of problem I have now. It seems the spark ignition is coming too soon. Not a miss but a firing against the piston on the compression stroke. Feels like I am hitting the brakes.
This corrected with a plug gap adjustment and a new Speedo gear.

Lately I put on new tires/wheels, which have my Speedo running maybe 2-3% fast. That is when this started to happen again.
Unfortunately there is no larger Speedo gear for my truck and it would require complicated (and expensive) electronic correction. Not worth it to me for the little off the Speedo is.

All this leads me to believe this has to do with the timing. With the Superchip advancing the timing and the Speedo also advancing the timing, it may be getting so far ahead of the piston at high rpm that I am getting this misfire.
I am going to go thru the ignition this weekend and check the plug gaps again (plugs only have about 20,000 on them). Recently went thru the fuel delivery system including new fuel filter.

I may need a re-burn with a little less timing advance. It is running very good now, almost like when I first got the superchip. I still want the higher rpm shifts, the elimination of the timing retard when shifting and the speed limiter removed.
Will let you know...

 

WLF

Is it a stock program? With 4:30 gears I would think you would need to have the Superchip reburned to compensate for it.

 

Yes stock program. When I did the gear change, talked to Mike and he said with the speedo correction the chip would also be corrected. He was right. Problem now is the speedo is off a little and it probably will not be corrected.

 

Hi WLF,

Thanks for your response.

Yes, the Superchip does advance the timing as part of it's retuning the engine specifically for premium gas, you're absolutely right about that of course.

There should not be anything else on that vehicle that affects timing when the Superchip is installed, it's spark maps are designed to work with the vehicle's timing at the factory spec, always. I don't know exactly what kind of set up you may have there ignition-wise, but most aftermarket ignition systems cannot advance timing in these vehicles. There are a few special purpose ignition computers that will remap spark timing on the fly, but that's a completely different type of component. Your "normal" Accel, MSD, etc. aftermarket ignitions, the vast majority cannot advance timing on these vehicles, usually they only allow a separate rev limiter (or 2 or 3 different rev limiter stages) or a timing *retard* tied in to either boost pressure (as in forced induction motors) or a retard that is rpm-based (skipping the starting retards some units offer to help fire a race motor), & that type of thing. Perhaps you have something different going on there in that regard, we can talk about that when you call.

Timing is not altered by tire size, other than the natural effect of turning more or less engine rpms for the same vehicle speed as a result of the effective change in final gearing from the tire size change. The *load* is certainly altered, as are engine rpms, speedo & odo accuracy, and the auto tranny shift points in some cases aren't optimal, depending on just how far off the speedo is.

Interesting.

We'll go over everything when you give us a call & see just what's up.