I have a heavily modified 1991 350 TPI and it was running great on Saturday. Today I popped the memcal out to adjust the startup enrichment and when I put it back in and started the car it ran and drove like crap. Barely started, had to keep on the gas.

Drove around the block and at WOT the RPMs would barely climb then it backfired. Smells super rich. Tried a spare 730 ECM I had with no change. Re-wrote the PROM multiple times on 2 different chips and every result was the same. I used a known good tune.

No codes are tripped, checked timing, it was bang on steady with the est connector disconnected. With the est connected and engine running the timing showed advanced, but reving it up didn't make it move much. I think it was around 20 degrees with the connector connected.

Changed coil and no change. The car bogs, backfires, and feels like the timing is way off, but none of that was changed.

Through all of this the tach was working fine, but now it is going crazy. It was stuck on 0, then when driving it started working, then it was jumping up and down. Never higher than actual RPMs though.

Here is a video of the tach:

https://www.youtube.com/watch?v=_CF2...ature=youtu.be

Are these 2 problems connected as they showed up at the same time?

Is it the memcal/tune/ecm or distributor?

What would be causing the tach to act like that? It gets the signal from the distributor, so that must be the source of the bad tach?

 

This is where I would start.

i/e use your old tune.

Unsure if tach is related, but can't see how dropping the ECM would affect that.

Start over from where you began when it was running right.

 

Another thought...are you using a EEProm?

They are not "forever erasable and programmable"

Could be causing an issue.

 

I tried a previous working tune, the stock tune, and a tune already on a chip that Tuned Performance made me and the car ran exactly the same every time. I dont think it is related to the tune itself.

 

I'm using 27SF512 chips from Moates. But the tune on a chip from Tuned Performance has never been erased and re-written.

I even read the chip in the car and checked it against the buffer and cross checked it with tunerpro and it all seems to check out fine.

 

crap running and a bouncing tach are often symptoms of a bad pickup coil in the dist, or simply a wore out dist. a bad one can run fine until it gets a good rev it wasn't expecting or gets hotter than it's used to. I'd try a known good dist.

 

That is the plan today. I am going to get a working distributor and try it. Is it worth it to swap the pickup and modual into the one in the car or just pull it and drop a different one in?

 

Try a complete new dist. Sometimes the old dist can have enough play in it so that a new pickup won't fix it. If that works you can try a new pickup on your old one and see.

I've had no issues with several reman small cap dists that I've installed over the years. Run around $100 and usually come with a new ICM.

 

So the plot thickens. Put a new dizzy in and the symptoms are the same. But when I ran the engine and adjusted the timing I found all 4 passenger side header tubes cold to the touch after it ran for 5 minutes...

The passenger side of the engine isnt firing.

Both 10amp injector fuses are good.

 

fuel issue somewhere in the wiring most likely, can't imagine anything in the ignition that would only affect one bank, unless the plugs there are sooted up REAL bad.

recheck everything you did and see if anything could have been done that would affect the injector pulses to that side.

 

I have spark to both sides of the engine. Only verified with a timing gun strobing when hooked to each wire one at a time.

I don't have a noid light to check if the injectors are even getting signal. Any other way to check them?

Maybe when I pulled the computer down from under the dash a wire got pulled. Everything looks ok though.

Both injector banks have 12v at the pink/blk wires at all the injectors.

 

ECM provides the ground signal to fire the injectors

 

Is it the ECM that has the injector drivers? I tried a different ECM and its the same situation. If the PROM was bad would that affect injector control?

I rigged up a small light bulb across the injector connector terminals and with the car cranking and running the light didn't come on.

 

Probing the injector wire right from the harness at the ECM shows no grounding signal when cranking or running. How can only 1 bank be not working?

 

Since TPI is batch fire, a relic from the Stone Age, one bad connection can take out one whole side of the engine.

I'd be looking at the connector at the ECM, which was disturbed to some extent while changing the chip. Wire pulled out of the pin, connector loose to the ECM, broken wire near there, etc.

See my signature for a helpful mental discipline during troubleshooting.

 

Bingo! Soldered connection inside the heat shrink on the injector power wire was pulled apart. Soldered back up and the engine works great...

Tach is still stuck on 0 though. Any thoughts on that?

 

You find out what was wrong with your tach?

 

Its working fine now. After driving around for a bit it started working. It was still bouncing around for a day but has smoothed back out. I have no idea why it was acting crazy.

 

My tach did the exact same thing once. I fixed it by giving the negative lead a few extra turns on the batter post. Check all your ground wires.