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I have just installed an OEM TBI fuel injection on the 250ci inline 6 in my '57 Chevy Suburban. I have modified the coil-in-cap HEI distributor to be run by the ECM.
I have gas at the throttle body but not much sparks.
I have pulled 3 spark plugs (1 at a time) to check for spark, cranking the engine, and:
1 spark plug has spark often, normally, it seems;
another spark plug had spark some times, like 4/5 sparks then none for a few seconds then again a few...
yet another spark plug had only one spark over the 10-20 seconds I was cranking the engine!
With my limited electrical knowledge, this does not make sense at all!
Plugs, plug wires, cap, rotor are new; coil is not new but worked a few months ago, module is junkyard used
Can anyone help?
Thanks!

You have so many possibilities .I would start with the wiring to the distributor ,is the distributor the correct part number with the ECM ? Tell me also where you found the information to guide you ? You said that the distributor was modified ?What did you do to it ?If you want a faster answer try calling street and performance at 479-394-5711 ask for Mark he will point you in the correct direction .Also give me more information I will help also.

http://www.ifsja.org/forums/vb/showthread.php?t=69362

This is the main place where I have found instructions for modifying the distributor (about half way down the page); I simply used the distributor that was on the truck before, I am using the 8-pin module, mounted outside the cap; I use this module because it is the style that came with the harness I found at Pick'n'Pull, from an '88 1/2-ton (ECM and all sensors from same truck). The 02 sensor is not connected yet because my exhaust pipe is not built yet.
I guess in this case, I would understand better if there was no spark at all, but only some spark, in some spark plugs? Strange...

Did you program the ECM ? Also did you check the wiring after installed with a ohm meter .Checking for any breaks. Timing on the engine and computer are they matched ?

Are you getting a full 12v to the coil?

Larry

I did not change the chip in the ECM, it seems a chip is not an absolute necessity; I do not know how to check the timing; everything not part of the EFI harness is as before on the truck, as such, I still use the same wire to bring electricity to the HEI, directly from the ignition switch.

Uh, i would learn how to set timing first.

I have not taken the distributor out to modify it, I have made sure I did not rotate it and all was working fine before. And now the module/ECM should take care of timing...

Anyone in Calgary, Alberta, would like to come and take a look at my truck? I am getting frustrated right now!!!

Here's a link to Jags That Run, they have been dealing in Chev EFI conversions for a few years and have manuals on doing the conversion;

http://jagsthatrun.com/OrderingBooks.html

Hope that helps.

Larry

How do you set the timing on any engine with a distributor? With a timing light.
You do have to pull the EST wire connector apart.
From that jeep forum link you posted.

>>7. Pin B - is the override cranking signal pin. This pin needs a wire connected to it that runs to the GM distributor connector wire that is tan.<<

Whatever that means, but it goes to the EST port on the ECM.
That wire is Tan or Tan/Black strip. There should have been an in-line plug, that needs to be separated in order to set the base timing of probably 6 deg. When you plug the tan/Black wire back together, the computer will move it to where ever it thinks it needs to be.

Have you checked for fault codes on the ADL plug?

One very common problem with these type of conversions is poor grounds. You must have good grounds between the engine and the frame and the body and the ECM.

I know which inline plug you mean, for the timing check, but I have not removed or move the distributor, could the timing need be so different between the oldvaccuum advance and the ECM-controlled timing?
There are no trouble code since the engine does not run, bummer...
I guess I will have to go and check grounds again, too...

Well, I have checked the coil and the pick-up coil, they are good; I have swapped the module for another used one and swapped the ECM: nothing changes.
Indeed the coil could be damaged inside in a way that does not show on the ohmmeter, maybe I should change it?
What else is there?

I had a TBI in my 1991 truck. For some unknown reason, two different coils at two different times suddenly failed. The module was never bad. Consider a weak spark no spark.

So, here are the latest news:
The engine still does not start: the starter spins quite nicely, I have no spark and no pulse at the injectors (they do have ignition +, just no pulse).
Following advice from this forum and ideas from the shop manual, I have checked everything:
I have continuity on all the wires, all the grounds are good, TPS, IAC and MAP, coil and pick-up coil are good, the ignition module was checked today at the parts store; coil, cap, plugs and plug wires are new. I have gone through all the wiring (I think...), everything is where it is supposed to be. I have tried 2 different ECMs. The O2 sensor is not connected because there is no exhaust pipe yet. I have no trouble code because this combo has never run.
So what now??? What is happening, what do I have to look at? What am I forgetting?
Thanks!

You should be able to induce a distributor reference signal to to ECM. When the ECM detects a distributor ref signal, it WILL pulse the injectors. I think you're not getting a signal to the ECM. I had two bad computers in a row. You cannot guess. You must test.

I'm not sure which ECM you are using, but all GM are similar. A GM service manual for the system you are dealing with will be invaluable. FACTORY SERVICE manual.

Have you checked the crank shaft position sensor ? I've seen them fail & the engine will still crank but not fire

Thank for the input, guys!
There is no stand-alone crankshaft position sensor on an '88 TBI engine; I believe the distributor does that.
As for your comment about the ECM not getting a signal from the distributor, indeed, it makes sense and goes with the idea that the pick-up coil could be the problem, since the module tested good at the parts store a few days ago...
I have tried 2 junk yard computers, I guess they could both be bad (although SES light and fuel pump work), but then, how many do I have to test until I accept that it is not the ECM??
On the other hand, the ECM is "not used" until the engine reaches 400rpm, so it feels more like a distrbutor issue (back to the pick-up coil) than an ECM issue.