I probably posted this on under the wrong heading previously, so I'm re-posting it here. New to this thread.

Hi. I'm new to this site, and not real sure how to use it, so I hope you bear with me. I have a "crank but won't start" condition with a '87 TPI system. Some background-383 sbc in a 1941 Chevy coupe. '87 TPI from a Trans Am, Hi flow Edelbrock manifold,Large runners, 52mm TB, Pro Comp Aluminum heads, Comp cam, etc, etc. Everything on the car is new (almost) as it is a frame off build. New car wire harness, new TPI harness, new ICM, new pickup coil, all sensors check good. I have checked all wiring for continuity-good. I have secondary spark, 12v at the injectors, but no pulse signal at injectors. I have checked all pins at the ECM for correct voltage and all are in range with exception of pin A8-Serial Data, which shows a flashing O.L. on digital VM. It should be 2-5v. This is a mystery. I have checked what I could with a Snap On Advantage Pro osilliscope, and can't get a reading on pin B5 which is the Dist. reference wire. (Prp/wht) I do get a v. reading when cranking of around .470 on this pin. Everything points to a bad module, but I've tried 2 new ones and 1 used one that all checked good at Auto Zone. This motor has never been started. Everything is new. I had the eprom programmed, and wondering if something in the prom would cause a no start condition. No VATS in '87. Anyone have any ideas? I'm at a loss. Any help is greatly appreciated.
Sorry for the long post, but wanted to give all info right away

 

Without a DRP on B5 the ECM won't fire the injectors. Double check that the module and coil and injectors is getting +12 volts at both key-on AND cranking. Since this is swap it is easy to use an IGN+ that is only hot in run, and not hot in cranking.

RBob.

 

RBOB, Thanks for reply. I have 12v wire tied in to 12v coil wire, so is hot in on, crank, and run. And yes, that's the problem-no signal at B5 pin. Everything is getting 12v. Just no pulse signal. Prom?

 

No signal at B5 is entirely on the distributor. Can unplug the ECM and will still get a DRP on B5.

The DRP is generated by the ignition module each time it gets a pulse from the pickup coil. The pickup coil generates a pulse each time the 'star wheel' passes the reluctor posts.

You can trouble shoot by pulling the distributor out. Ground the distributor body to the engine (this is important). Then key-on, engine-off and spin the distributor by hand. As you do this the injectors should fire along with the coil generating sparks.

The fuel pump should also turn on each time this is done then turn off 2-seconds after the distributor stops spinning. So keep in mind that you can flood the engine doing this.

Can unplug or pull the fuse for the fuel pump to prevent flooding the engine.

And a path for the spark from the coil needs to be provided so that the coil doesn't arc internally.A spark plug stuck in the coil wire and laid on the engine works.

RBob.

 

RBoB, Thanks for that procedure. I will try it, though I have tried 3 different modules (2 new) and the pickup coil is also new. But this procedure will eliminate the possibility of losing 12v. when key is in crank position. Will let you know how it turns out.

 

RBob, tried checking things with dist. out. Still no pulse signal. With all injector connectors disconnected, should you have 12v. on both pins-pnk and bl or gn?

 

I think that you will read +12 on both pins of the injector connector. The one pin should have +12 IGN switched on it. The other pin gets some feedback from the ECM so that it too may show +12 volts. If it does or doesn't I wouldn't worry about it. As long as the IGN 12V is there.

With the distributor, a small cap gets power to the coil via the heavy pink wire (from IGN +12). The module power is from the white & pink pair of wires from the other coil connector. The coil end connector sometimes fails causing no +12 to the module.

If it is a large cap distributor I am not sure of how they are wired. Other then the heavy red being the IGN 12V feed to it.

Just don't forget to ground the distributor body to the engine while testing with it out.

RBob.

 

RBOB, Yes I have grounded the dist. while checking things. The module is getting power, and there is 12v. on both sides of the injector connector when they are all disconnected, I just wasn't sure there should be, as the pulse has to be activated by a ground. I'm at a loss.

 

Is there spark when you spin the distributor? There should be.

RBob.

 

Yes, I have secondary spark, just no pulse. Injectors apparently aren't getting grounded. Blue and green wire from ECM to injectors have continuity, and everything else seems good. I've checked the grounds, even ran another ground from body to engine. Nothing seems to work. I have some spare injectors, and tomorrow I'm going to hook one up and see if I can get it to fire somehow. Any other ideas?
Smoke29

 

The DRP on B5 is a 5V square wave signal. Best to use a scope to look at it. Without a DRP the ECM won't fire the injectors.

Check it at the module first. Then at the ECM. The wire or a connector may be bad.

If you find that the DRP is present at the ECM, then check the PROM BCC. Never know, it may be from an early y-body which got VATs before the f-bodys. Or, it may be an '89 f-body PROM.

RBob.

 

As I said before, I have checked B5 with a Snap On Vantage Pro Oscilloscope, and it won't give me a reading. I only get a reading of around .470 V while cranking with a meter. I have checked it at the module and ECM. I've checked continuity and wire is good. When you say DRP, does that mean Distributor Reference Pulse? And what is the prom BCC stand for? How do I check that? I'm pretty sure the prom is a '87 F body by the code on it. I also had it programmed for my motor, so if it did have VATS, instruction were to remove it.
I appreciate all the info your giving me.
Smoke29

 

The BCC is the PROM code, such as ARAP, or ARAR, AUJM, and so on.

You can disconnect the 4-wire plug from the distributor that goes to the ECM. The ECM isn't required for the testing. With spark that shows that the distributor is getting power, and that most of it is working.

No DRP but getting spark is on the ignition module. DRP is the distributor reference pulse. Maybe the ECM is bad and is interfering with the signal. Which is why I mentioned unplugging the 4-wire connector at the distributor.

Maybe take the ignition modules to an autozone or napa where they can test them.

RBob.

 

Sorry to be a pain, but my previous post told you I have done all those checks. Tried original ECM and when I couldn't get it going, and things seemed to indicate a bad ECM, got a new ECM, have tried 2 new ICM and 1 used that all checked good at Auto Zone, new pickup coil, all new wiring, checked all the grounds. When you say "You can disconnect the 4-wire plug from the distributor that goes to the ECM. The ECM isn't required for the testing." What test are you refering to?

 

Observing the DRP on the scope.

RBob.

 

OK RBob, I'll try checking the DRP at the dist. with the connector disconnected and see if I get a signal that way.

 

Sorry guys for jumping in late and asking "This dumb question" BUT..........did you(smoke29) properly ground your engine too the chasis??? Do not rely on the engine mounts to ground your engine. Use a proper gauge wire for grounding. And make sure that the Battery is properly ground too!

 

Yes, all the grounds are there. Separate cable for engine to frame, and body, and battery. Thanks for the thought though.

 

Hey smoke29, did you ever figure this out? I am having a similar problem and have spent hours reading posts. I have performed the same tests and I have the GM service manual and followed the flow charts. The charts say bad ecm, but I do not want to buy an ecm and find that the car still won't start. I have a stock 91 TA convt 5.0 tpi, the car sits all of the time and I pulled the coil wire off the coil and turned the engine over to build oil pressure. I then reconnected the wire but, the car wont start. I had done this once or twice before with no prob. There were no other modifications done to the vehicle and it ran flawlessly about 4 months previously. I have spark, have proper fuel pressure, but fuel injectors have 12V contstant, even when cranking. So the ecm is not grounding the injectors. I get about 1.2V at the purple/wht reference wire to the ecm and the GM manual calls for 2.3V. I did just replace the module as a cheap diagnostic test, but still no pulse to injectors. My next step is replacing ECM, but my gut tells me it is not the problem.

My initial thoughts on your situation: you mentioned that you still had the stock ecm and tried it. Was the harness also stock? here is a link to another discussion that ended up being a VATS issue, but the discussion is pretty informative. https://www.thirdgen.org/forums/tech...cranks-no.html

I am not sure how to get back to these posts, but I'll try. You can also email direct at sales@fpmarine.com good luck, Ken