My 89 corvette TPI engine installed in a 1951 Chevy runs great one day and not the next. I can not get the engine timed correctly. I covered all the basics for timing with out avail.

 

Assuming you set the computer over to the new car correctly, what exactly do you mean you can't get it timed? Does it change timing? It should not if you set it by removing the tan wire first, setting it to 6 degrees and then reinserting the tan wire into the correct place.

 

When you disconnected the EST connector (tan wire with black stripe), that disconnects the ECM from the ICM. The only thing controlling the timing is the ICM. There is no timing added when at idle speed.

 

The ECM prom was reworked by Tempe speed shop . I do disconnect the wire mentioned. The cam and crank position was recently checked. When attempting to time I reach 6 degrees BTDC the engine runs terrible. I advance the distributor around far when finally reaching a position where the engine will idle some what smooth there is no power.


One other observation; I just got the mufflers installed, prior to that the car was some what drivable, after that run really bad. Sounds crazy!

 

I have a sinking feeling that the distributor was set in on the wrong tooth

 

I thought it was an electrical problem due to the drivable/not drivable condition. I thought about the ICM, its new, no place that can test. I have also gotten various codes 43/42 It seems like they come and go.

 

I have looked at that as well. No longer trusting myself I ask a competent friend to check, he felt all is well.

 

ASSUMING he redid the timing just to be sure, how sure are you that it is done right? Did he install it correctly? Was your timing mark good? BOTH must be good for this to work

 

yeah. this ^^

did you verify your TRUE tdc position by using a piston stop? I did mine, using a video here:
i used a random combonation of nuts bolts and jb weld left overnight to hold it all together.


and then used it like this:


and this guy talks about why it might have been moved:



and once you have marked your hb with the true tdc position (in my case, it was ok, hadn't moved) then you need to set timing again.

with the mark on the balancer confirmed, you can verify that your rotor is pointed directly at the #1 terminal.

Once that is confirmed, if you are having intermittent running issues, my own next step would be to double check all grounds. it was an engine swap after all so there could have been a botched ground (among other things)

if grounds are good, i'd be putting an aldl scanner on it, and seeing what the readings are when it craps out on you. if you have a sensor that has gone haywire on you reading ***** nilly, like a cts, or a tps, or an iac or a maf (were they maf in 89?) or a egr that suddenly opens at idle...then you should be able to narrow down your issue.

here is my tdc tool:
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Hi

It is quite common for the harmonic balancer outer ring to slip, usually the outer ring also moves back toward the timing case cover.

Confirm the no 1 piston is all the way up and that the distributor rotor points to no 1, the correct way is to rotate the engine with valve cover removed. Watch the inlet valve open and close and when the piston is at the top, that is TDC and the distributor rotor button is pointing to number 1.

I would think the most likely issue is the harmonic balancer outer ring has slipped, setting to TDC is the piston all the way up?
You can check this with a coat hanger wire poking through spark plug hole, that will confirm if the harmonic balancer has slipped or not.

By adjusting the timing to what you think is TDC could be way off, your engine is running so should be in the ball park.
Just set the distributor to where the engine runs best.

Do you have any fault codes?

 

You can still set the timing successfully. The distributor will be off by 15 or 20° but it doesn't matter as long as the rotor is pointing at the correct terminal when it's time to fire the spark plug.

You can tell if the distributor was inserted correctly by how the top of the cap aligns with the firewall. If it's correct it will be parallel with the firewall (or 90° to the centerline of the engine).