Started the car today after sitting from a 30 mile trip. Got on it, ran really bad and then just died. I tried to restart it and it was knocking (spark knock) and was belching black smoke. Then absolutely nothing. Cranks good but woth start. Turns out the injectors are not firing (Fuel pressue is good) and I have no spark. The Vettes have an oil pressure switch where the FP will not activate when pressure is less than 4 psi. That all checks out good. I checked the ECM grunds and they look good also. I have trouble codes. In diagnostic mode I have a code 12. I have VATS and it is working properly so diacom reports and if it was not working, I would not expect it to crank but I would expect spark. I also have 12V going the red lead wire in the the distributor. I changed the ignition module. I verified that the injectors were not firing by measuring volts while cranking and all my plugs are bone dry. They are also sooty which back up it running real rich before quitting. I tried a back up chip and thats not the problem either.

I know the ECM controls the injectors and timing. But what I don't know is if a faulty ECM can cause NO spark at all. Any opinions as to what my next logical step might be? I'm leaning towards swapping in another 7730. Comments?

Thanks,
Jason
396 Minirammed Vette

 

A faulty ecm can have no spark, or fuel.
There will be no fuel without a reference pulse, double check the pickup coil in the distributor, should have 600-1K ohms resistance.
This is one of em times I mentioned having a spare ecm is more then just nice.
Todate, I haven't heard of anyone reverting back to a 165 after installing a 730.

 

I'm not converting back to the 165. While cranking, Diacom shows a zero injector pulse. The fuel pump relay will not energize unless it sees reference pulses from the distributor. While cranking, the fuel pump relay pulls in which tells me the ECM is seeing reference pulses. I'll check the reference pulses though. I get this ECM from a junk yard and its only been in for about 5 weeks.

Thanks

 

I was looking at my shop manual and there is basically 4 things to check (which you have done some already). One is fuses and fuse link. But since your ecm does appear to have power, this does not appear to be a problem. Another is the ALDL circuitry to the SES light. If your SES light is on when you have the key on, but the engine is not started then this is not a problem. Third is the PROM, which you have swapped. So the only one left is the ECM, as you suspect.

Might want to consider getting a spare this time. I hope you have better luck with the next one and the ecm is the only problem.

 

I too would look towards something ignition related rather than the ECM, if your getting 12's that is basically saying its fine, but as stated above, it IS possible to have something wrong with the ECM.
I noticed the same rich condition/black smoke on a friends f*rd escort wagon a few years ago. He doesn't know anything about cars so eventually we got it figured out and that was the problem.

Let us know what you find out.

Brendan

 

Glenn,

I have a steady SES light with the key on. Yes the ECM seems to have power and is workign properly as far as Diacom shows. The ECM seems liek the next logical step.

Jason

 

Given their cheap cost (when from a 3.1 Cavalier) and ease of swapping, I would go that route first.

BTW, what other codes besides "12" did you get?

 

Glenn,

No other codes besides code 12. I did have a strong odor of something burning up that I can't ignore. Someone on the Corvette Fourm brought up a good point about a possible burned up fusable link. I need to check for 12V at the injector harness with the key on.

Jason

 

Jason, I thought about that option (see my earlier reply regarding fuse and fuse link) and if your fuse link was gone, I don't think your ecm would be functioning at all. That is why I elimated it as one option.

That "whiff" of "burnt electronics" suggest the ECM to me. Fried electriacl components have a very distinctive odor. You should "sniff" inside the ecm (don't laugh) to see if the smell came from there. Based on what you just said, the ecm is starting to sound more like the culprit (or a fried connection somewhere in the harness) from/to the ecm.

 

I'm not below sniffing my ECM. I have another one coming tonight to try. I'm hoping its not a burned up harness somewhere. I'll report back tomorrow. If the ECM is not commanding an injector pulse, then it seems logical its the ECM. If it did burn up, I'm going to worry why it burned up. Of course I'm always worrying about something!

Jason

 

Sniff the ECM - roflmfao. Very funny and very good advice

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Hmm, is it possible to tap into the injector driver wire coming from the ECM? See if there is a pulse coming right from the ECM while cranking..?
Did you check your injector fuses in the fuse box also?


Brendan

------------------
1987 IROC-Z L98,SR,EB 6085's,LPE 219/219 SR Cam, Crane 1.6RR, EB TPI Base, 58mm TB, Stock T5, ADS 24#, AFPR, K&N, EB TES, Catco Cat, 3" Borla Cat-Back, Accel cap,rotor,distro/other crap, Aluminum DS, 94 Disk Rear, Adjustable Prop Valve, Precision 3.73 Gears, Weld in Sub-Frame Connectors, Hotchkis LCA's, KYB Shocks/Struts, Poly Bushings all over the place, Moog Upper/Lower Ball joints and Tie Rods ends/Idler Arm, Big stereo, 730SD Conversion.

To see the ROC, Check out the webpage Here

 

Back in the early 80s when I was involved in importing a bunch of "Apple II Clones", we use to experience a 20% failure rate. 9 times out of 10, I could identify the IC that blew by "sniffing" and feeling for a "blister" on the IC.

It sounds funny, but was quite effective. Once you smelt one of those (burnt IC) you will NEVER forget the smell.

 

Well its not looking good. I swapped in another ECM and I get the same thing. Car will not start. I disabled VATS no go. While watching Diacom while cranking, I get no injector pulses and my timing reads zero. I loosened the distributor and and twisted it and the fuel pump energized. This tells me the ECM is seeing a a pulse. For the heck of it, I ohmed the pickup coil per the service manual and it checks out ok. I also used my volt meter and checked all grounds against the three power feeds into the ECM. All checked out good. So I have power,and good grounds. I smell nothing burned.
At this point, I have no idea where to turn next. Something is causing the ECM not to command fuel and spark. But what? This makes no sense to me. For what its worth, everything in the car works like all the lights, radio, blower, etc. I need some expert opinions here. I realize this is off topic and does not seem prom related but its ECM related and I hope that counts.

Thank you,
Jason

 

Have you checked for fuses, maybe injector fuses?

Oh did you do the ecm swap to allow for going back to the MAF setup??
Just for testing purposes of course. That would rule out all of your soldering connections and anything you "may" have done when wiring up the SD ecm.

Brendan

 

Jason,
I was sitting here rereading your post and I thought for a second. You wouldn't happen to have an MSD box or any other aftermarket ignition would you??

If so, try a stock coil. Believe me, I've had my fair share of let downs with my POS MSD box, thats why the harness got cut off and its sitting in the garage right now.


Brendan

 

Jason
When you turn your key to on ,Do you hear the fuel pump for a few sec?/ It should prime the injector rail??
I have never done a diacom recording while starting the car. but sounds like I should to see what takes place.
The local auto should sell and injector check and pulse checker.
You plug each injecotr plug and it should pluse the test lite.

Since you have no commanded PW via diacom you will probrably not see a pulse lite.

Read above post. Check you rotor. They seems to come unscrewed with us 6 speed guyus alot.

------------------
85 vette,383,miniram,ZF6,4.10's..best ET 11.56@119.00 60' 1.59
w/100HP nirous 11.05@127
http://geocities.com/bowtie8
http://bowtye8.tzo.com

[This message has been edited by BOWTYE8 (edited July 18, 2001).]

 

Code 12s means the ecm has power, ground, and at least some processor functions.

When turning the key on, there should be a 2 sec fuel pump run signal.
There will be power from the fuel pump relay when the oil pressure is over X PSI.

For the injectors to pulse, the ecm must see distributor reference pulses.

If there is no spark, then there might be a lose of the refence signal so the injectors won't pulse.

Using the above clues you should be able to logic your way thru to narrow down the possible faults.

 

Dennis, that stuff is all good.

Grumpy, Ok now you have hit on something. Your telling me the the ECM does not energize the fuel pump relay based upon refrence pulses but upon OP being over 4 psi (per manual). Now it coming together for me. I remembered yesterday that I jumpered around the oil pressure switch to see what happened. When I did, the fuel pump energized. I assume that the FP singnal imput on the ECM is what the ECM uses to determine if the fuel pump relay has voltage. Hence the value in diacom displaying fuel pump voltage. OK so now I'm back to the pick up coil. I have heard that even if they ohm out good (which mine did) they sill can be bad. My next step then is to replace the pick up coil. If that does not work, then I need to start looking at the dist ref circutry back to the ECM. Thanks for that great information. I'll report back tomorrow with the verdict good or bad. Teh worst part of this whole experience is I have really caught on to SD tuning. That day it crapped out was the best its ever run. Go figure. Is there anyway to verify a reference signal? What tyeo if signal is it?

Oh wait a minute, I forgot something. I forgot that the fuel pump energizes (like a start up energize sequence) when I spin the distributor. What causes this? I assumed it was seeing a pulse.

Jason
Jason

 

My next step is still to replace the PU coil. However, in studying the wiring diagram, I still seems to me that the fuel pump can be energied by the ECM hence on start up it runs for 2 seconds. Now when I twist the distributor, the fuel pump energizes for 2 seconds like on start up. The only circutry that I see that will casue this is a distributor reference signal. Grumpy do you agree? Does the ECM only energize the fuel pump on start up and after that the oil pressure switch takes over? Looking at the diagrams, this seems like it would have to be the case. I'm just trying to logic my way through this so I may plan my next step if the new PU coil does not work.

Thanks,
Jason

 

Could have a bum wire in your harness, or the connector. If anyone near you has a spare distributor for you to try, I'd go for that. Sounds like pickup or wiring to my not-so-educated guesser.

 

This is a worst case scenario, but have you checked to see that the rotor inside the distributor is actually turning when you crank the engine? What if (God forbid) the timing chain let go?? This could cause all these problems - but like I said - worst case scenario - Or it could be the ignition module, not the pickup coil, if the module goes bad the ECM won't see referance pulses, just another possibility.
Good luck.

------------------
Karl Hunter
Hunter Motorsports
Vancouver, B.C. CANADA

 

Nevermind about the Module, I noticed you already changed it.

------------------
Karl Hunter
Hunter Motorsports
Vancouver, B.C. CANADA

 

As usual, I want to thank each and every one of you for your help and support. This is a great Forum with great people always willing to lend a helping hand. After a frustrating night, and after replacing the pick up coil, the car fired a couple times for a few seconds and then just died in an instant. To make a very long story short, I finially realized that in addition to no timing, fuel and tach displayed in Diacom while cranking, I had no tach signal to my instument panel tach either. Even though my coil ohmed out good, I replaced it with one I had sitting in the garage and it fired right up and idled there for about 20 minutes. I started it numerous times and it hits right away every time. Then I put it away. So it seems after all of this my coil was the culprit. I would have never guessed that the coil could cause the ECN to do nothing. I would at least expect it to go through the motions since I was convinced it was seeing a referece pulse. Anyway, for right now it seems I'm back in business and ready for some more tuning!

Thanks again,
Jason

 

Glad to hear you got it running. Having never had a bad coil on an EFI car, this is new information for me to remember.

I think I will do a Diacom capture of what happens when I disconnect a lead to my coil to see all the things Diacom displays so I will know the "things to look for" if this ever happens to me, or someone else.

You've definitely have had an "uphill" battle: First, getting PP to program your Flash Prom, then getting a decent "base" SD eprom to work, then you plug wires, and now your coil.

Oh well, it's always something, when it comes to cars.

 

Jason,
Good deal.
I carry a spare cap and rotor. I hear alot of the rotors coming lose. Mine included and can leave you stranded.
I think Greg has a good point. I will get some diacom on startup and with a my coil unplugged.

I know it a good feeling to be back on the road
Dennis


------------------
85 vette,383,miniram,ZF6,4.10's..best ET 11.56@119.00 60' 1.59
w/100HP nirous 11.05@127
http://geocities.com/bowtie8
http://bowtye8.tzo.com

 

I'm not disconnecting anything while its running! I would be interested in seeing what the ECM does also with the lead wire disconnected. Oh well, at least now I have a totally rebuilt distriburor. Now my master cylinder is leaking! Oh god what next!

Jason