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So as the title describes I'm having an issue where the ECM does not want to fire the injectors, or prime the fuel pump relay. I have ruled out many possible causes including the Ignition Control Module (replaced it), the ignition switch (tested and replaced not long ago), the fuel pump (ran on separate power source), the fuel pump relay (tested manually), as well as the injectors which I also tested manually with a battery.
The ECM is getting power from the ENG/CNTRL Fuse and the injector fuses all read voltage as well. All of the above fuses have also been checked, the whole fuse box has working fuses.
I'm trying to be thorough here because I'd like to avoid throwing more parts at the car in order to get it to work. My next step is to manually run the fuel pump in order to build pressure and manually open the injector (with a separate battery) to see if it squirts fuel. If that works and the injectors squirt fuel I know it's the ECM.
So until I conduct that test, can someone give me some advice on how to test if the ECM is bad or not? The car stalled on me all of a sudden a few days ago while driving and I had to get it towed back to my house. The car would crank but would receive no fuel. This same incident happened a few months back in a parking lot but after about 15 minutes fuel came back and it started back up again, like nothing ever happened. This time it's permanent.
Btw use a noid light to check forbinjector pulse. 12v to a injector is a great way to fry the coil. These schematices are for 89/92 1228746 but are the same as your service number 1228063 they are interchangeable ecms but 89 up has vats enabled in the programming. Hope the schematic s help.
Last edited by Tuned Performance; 04-17-2018 at 10:42 PM.
So I borrowed an OBD1 Scanner from a friend of mine and decided to read to PROM and hopefully get a reading, I got 'NO DATA'. Checked the power to the ECM and confirmed with a multimeter it was getting 12v. I decided I'd hit the junkyard and get an ECM from a TBI Truck. Managed to find a 1227747 from an 86 GMC and plugged it into my Camaro. It fired up with a little bit of help from the throttle and idled relatively well. I was about to swap the PROM chip from my old one into the new ECM but I wanted to go for a test drive first.
The second I put it into gear the car died because it was idling funny, then I tried to start it up and I got nothing. The new ECM which I had previously gotten a PROM reading from was now reading nothing for PROM data and all the same issues from the old ECM (no fuel pump relay prime, etc.) were now happening with the new one. The car would just crank and crank.
My thoughts now are that this car has spontaneously started 'eating' ECM's somehow. At the moment I'm thinking the 5vref pin on the ECM is getting powered by the car through some sort of funky wire crossing and that's killing the ECM's. This is just a theory pulled from what I know about aftermarket EFI controllers like the MicroSquirt.
If anyone has had experience where their car was 'eating' ECM's I would appreciate your input on how you fixed this issue.
The prom swap from $4d mask to $42 mask are not interchangeable. You should have a code 51. The 747 doesn’t use a iat too. You might want to check your grounds on the cylinder head . You can upgrade to the 1228746 if you get a prom reprogrammed with the vats disabled.
The prom swap from $4d mask to $42 mask are not interchangeable. You should have a code 51. The 747 doesn’t use a iat too. You might want to check your grounds on the cylinder head . You can upgrade to the 1228746 if you get a prom reprogrammed with the vats disabled.
Oh I wasn't aware the PROMS weren't interchangeable. Well in any case I'll check the grounds in the ECM harness connector and I'll see if the 5vref wire is somehow getting powered. Doesn't really change the fact that I now have 2 dead ECM's without a way to repair them
Checked the ECM ground connections and they all tested good, crank signal got voltage, battery input was good. Only connections that didn't get a reading were the sensor grounds because they are grounded by the ECM. 5v ref got a few mV on the multimeter but as I understand that shouldn't be a problem.
Did a bit more research on what can cause an ECM failure and found that shorted injectors or a failed ignition coil can burn the drivers out in the ECM.
I tested the ignition coil using GM spec testing and it tested fine. Probed the terminals of the injectors which should read 1.2 ohms or higher and got 1.0~1.1 ohms which means they're shorted internally, I'm gonna replace the injectors and fire it up with a new ECM and go from there.
I swapped out the injectors with a pair that I kept from a rebuilt 350 TBI engine that was running when I bought it. After everything was connected again I plugged in yet another ECM (7747) I got from the scrapyard and it fired up again, idled pretty smooth too until it died after about 40 seconds of run time.
Again, scanner got no data from the ECM and it was fried. So far I've discounted the injectors, the ignition coil, the fuel pump and the ECM grounds.
My buddy suggested the fuel pump relay (which was changed this past summer) could be backfeeding 12v to the ECM killing it. Another culprit I thought could be causing the issue is the TPS sensor, it could be backfeeding 12v through the 5vref killing the ECM that way.
I'll test the TPS and the Fuel Pump Relay in case they've failed (even though they've both been replaced months ago)
Again, if anyone has any suggestions as to why the car is killing ECM's please let me know.
What about the wiring harness shorting out somewhere? It would be a lot of work but if you pulled the ecm connectors off and check each wire from ecm to sensor, relay,etc.
What about the wiring harness shorting out somewhere? It would be a lot of work but if you pulled the ecm connectors off and check each wire from ecm to sensor, relay,etc.
That may be the next step, a spontaneous short to ground seems unlikely to me but stranger things have happened before...
I'm going to test the Fuel Pump Relay and TPS sensor for feedback to the ECM, if they test ok I think I'll start probing each ECM connection to it's location and look for a short.
I'm planning on converting the car to MicroSquirt once I'm ready to drop in the new engine, but I have to find the problem first, because I definitely don't want to fry my MicroSquirt.
Just finished probing both ECM connectors to a ground source looking for readings and here's what I got:
Note that I removed the battery from the car and left the positive and negative cables suspended. I double checked the positive cable to make sure it wasn't contacting any metal to ground it. Also all of the red highlighting are connections we can rule out because they are supposed to be connected to ground. (O2 Sensor Removed)
At the moment I'm suspecting the fuel injector wires are grounded somewhere along the line, because across pins C15, D14, D15, and D16, they all read the same resistance value (~6.6 ohms). This would probably cause the injector drivers to burn out due to too low resistance (ground) which could be the root of the problem.
That's just my guess, I'm welcoming feedback with open arms!
FluffyK, does the SES/CEL light turn on with a quick blink off at key-on, engine-off? Can try again after at least 20 seconds of key-off.
If the SES/CEL doesn't do that then either the ECM is dead or it isn't getting power.
You asked about blowing up ECMs. A bad alternator can do that. When bad they can output up to 90 volts, not good. Spark plug wires routed close to the ECM harness wires is also bad.
FluffyK, does the SES/CEL light turn on with a quick blink off at key-on, engine-off? Can try again after at least 20 seconds of key-off.
If the SES/CEL doesn't do that then either the ECM is dead or it isn't getting power.
You asked about blowing up ECMs. A bad alternator can do that. When bad they can output up to 90 volts, not good. Spark plug wires routed close to the ECM harness wires is also bad.
RBob.
The SES light did nothing when the ECM was fried. Voltage from the alternator before the ECM's fried was 13.5 volts. Like you said the ECM is either dead or not getting power, however all the power wires (including the ignition wire) tests fine withe the multimeter, so the ECM is getting power. We examined the board and everything seems ok, no visible discolouration or obvious burns which leads us to believe it's a chip issue...
Gonna try swapping the whole MEMCAL out for a new set from the junkyard and see if it fires up again, here's some pictures of the ECM board. (original 1228063)
Have something for you to try, plug in an ECM, do a key-on, engine-off and check for 5 volts where shown in the picture.
Can use the big heatsink for a ground (a threaded hole is best).
This will prove or not that the ECM is at least powering up. I wouldn't be surprised that the terminal at A6 has an issue. Voltage from the ignition switch to that pin tells the ECM to power up.
Have something for you to try, plug in an ECM, do a key-on, engine-off and check for 5 volts where shown in the picture.
Can use the big heatsink for a ground (a threaded hole is best).
This will prove or not that the ECM is at least powering up. I wouldn't be surprised that the terminal at A6 has an issue. Voltage from the ignition switch to that pin tells the ECM to power up.
RBob.
Thanks RBob I'll try that out once I get the car back from the paint shop! That'll determine for sure whether the ECM is atleast getting power.
Ok I tried out what RBob suggested with the ECM on a bench with all the ECM grounds and Battery In and Ignition (A6) connected to a spare battery I had laying around. I probed the spot mentioned in the picture which should be 5v and that's exactly what I got. So the ECM is powering up fine with a battery. I'm going to perform the same test with the ECM connected to the car's actual harness and see if I get the same reading.
On the bench it is helpful to connect a SES/CEL light. Pin A5 provides a ground for it. So wire the other end of the light (194 bulb works) to +12 volts.
It it lights up then does a quick blink off, then on solid. The ECM is actually running from the PROM.
Just tested the SES light like you said RBob and I got a reading! It turned on for a second just like a normal "key-on" event and then it turned off right away. I also checked the fuel pump relay control wire and looked for 12v with "key-on" and it gave 12v just like a normal fuel pump prime.
The wires I have connected are:
A12 (ECM ground) to ground (battery negative)
D1 (ECM ground) to ground (battery negative)
and
B1 (Battery+) to 12V+ (battery postive)
C16 (Battery+) to 12V+ (battery positive)
aswell as the A6 (Ignition) to 12V+ (battery positive)
This told me there must be a power issue because I tested all the grounds in the car's wiring harness and they all tested fine.
So I found out that the fuel pump will prime and the SES light will work with just 1 Battery+ connection from the battery and the ignition wire, but it won't if only the ignition wire is connected (both Battery+'s left disconnected)
This makes sense to me because I don't remember testing the Battery+ connections on the car's harness, and they are connected to fusible links in the body wiring. Those fusible links could be broken preventing power from reaching the ECM. Or they may be flowing voltage, but as soon as too much current is drawn they "burn out" preventing the current flow.
I'm going to test the ECM's on the car again when I get it back since I now know they're working fine. I'm also going to test the Battery+ connections in the body wiring to make sure they're ok.
Thanks for the help RBob! I would never have figured this out without your advice. I'll report back.
Got the car back from the paint shop, damn does she look good.
Anyways, got the car back and plugged in the original ECM that tested fine on the bench (1228063), turned the key and voila! She fired right up, took a minute for the ECM to calibrate the afr and start running smoothly but it ran fine after about a minute. Just tried the other ECM I got from the scrapyard and it fired up with that one aswell, no issues...
I pulled pretty hard on the fusible links near the battery and the ones on the starter while the car was running and saw no changes. Banged on both ECM's while the car was running and saw no changes. I checked the grounds around the engine bay that connect to the ECM and they all look fine.
I've never been so irritated that my car starts and runs fine... However, since this problem is intermittent, I'm going to go for a little drive this evening and see if it stalls on me again. I'm kind of at a loss at this point because I was really hoping the issue would be the fusible links. At least if it stalls I can start to diagnose from there. Since the scanner I put on it didn't give me any codes I don't have much to go on.
Battery power for the ECM is via a 20A inline fuse. It is usually run along the passenger side fender under the hood. With the fuse close to the battery.
Next time the ECM is out check the ECM and the harness connectors for corrosion.
Battery power for the ECM is via a 20A inline fuse. It is usually run along the passenger side fender under the hood. With the fuse close to the battery.
Next time the ECM is out check the ECM and the harness connectors for corrosion.
RBob.
When this problem first arose I checked the fuel pump relay and confirmed it was operating properly, I ended up jumpering the relay so that the 12v battery connection (orange) of the relay was connected to the fuel pump connection. This however didn't turn the fuel pump on, even though the 12v connection read 12v+ on the multimeter. After reading your comment I realised after checking the wiring diagram that the ECM, Fuel Pump Relay and the Oil Pressure Switch are the only things connected to that 20A inline fuse. No wonder the ECM wouldn't turn on because the current from the 20A fuse circuit wasn't even enough to even run the fuel pump let alone the computer of the car. I believe this was due to a restriction in the current flow (possibly corrosion).
I did the 'pull-test' on all the harnesses that the 20A inline fuse circuit routes through and saw no change while the engine was running. I believe what happened is that the 20A fuse was faulty and broke connection while driving which stalled the car, however the break in the fuse was not visible (micro-break)
I replaced the old fuse (which was in the car when I bought it) with a new 20A fuse in order to eliminate the fuse as a possible cause of failure. In any case if this problem happens again I know exactly which circuit is responsible for the failure and can easily locate it in the wiring harnesses instead of having the tear apart the whole harness to find the issue.
For anyone reading this with the same problem (ECM not priming fuel pump, not pulsing injectors, or giving PROM data to a scanner) check the 20A inline fuse #3 circuit for breaks in the wiring along the harness or for a bad fuse. Remember: If a fuse looks good but the problem still persists, try another good fuse. You waste no money doing it and it may solve the problem, fuses can also be poorly manufactured.
Here's a wiring diagram with the 20A Inline Fuse #3 Circuit highlighted.
Thanks to everyone for all their help in resolving this issue!
04-17-2018, 09:58 PM
