I’m trying to figure out why my new to me l67 sc3800 swap isn’t running. It’s an 88 GT getrag combo. It runs on starter fluid. And runs well. But it won’t start without starter fluid. All testing was done on the rear bank only(cyl 2-4-6) There’s no injector pulse on any cylinder until it gets the ether. Then the noid light flashes and the car fires and continues running It won’t restart on its own.
I have 12v to the injector. Normal. Tested the pink wire to ground. Measuring across the inj connector I see 7 volts. I thought this was odd. If I remove the ECM fuse, the voltage goes to 12v across the connector. Edit: this needed to have a load to check. With the inj plugged in, I see 12V on each pin. This is normal.
PCM was tuned by Darth fiero. Harness by someone on here that builds reputable stuff.(Dan Mc) I have not contacted either of them at this point.
Thanks. I’ll add more as I go.
Edit to add. Fuel pressure is normal. The pump runs momentarily with key on and constant while cranking. Edit, Car Runs and drives once started(needs a clutch)
Wiring problems? (Lots of continuity checking!) If not, then which PCM are you running? I've had a '95 PCM go compleatly bonkers! I changed and repinned for a later '98+ PCM. No more problems afterwards😉
PCM's do go bad but before we arrive at that conclusion its time to hook up a quality scan tool to see what that says. If I were to guess it sounds like the PCM is not going into the cold start mode.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Sort of. I fixed a coolant leak so I could drive the car. I've gone around the block and to the gas station. Just enough to hit each gear and use the brakes.
One thing is that it runs and drives once started. For some reason people(not here) seem to glance over that. But it does start with starting fluid. It will run and drive at that point.
I put an old school O-scope on it since I don't have a scan tool. All of the sensors give a reading that looks good. HOWEVER...
According to this video, the 3x and 18x Crank signals operate on a 10V input giving a 7V square wave output. I'm only seeing about 5v output but have 10V+ input.
The ICM controls fuel delivery at initial cranking, and sends a voltage signal to the PCM to initiate the PCM fuel injector drivers.
Have you tried replacing the ICM?
Thanks for helping, I posted in some facebook groups and too many look past the fact that I said the car runs. They proceed to tell me to replace the fuel pump. Then people argue and chaos ensues. yes, I forgot to mention that there have been at least 4 ICM's installed, one being new.
All acted exactly the same. Statistically unlikely that they all were bad in an identical manner.
I've also checked connectivity to every wire I think is related to fuel control/delivery and the ICM. I don't have the paper in front of me to see what I checked.
here is a guide I was using for some troubleshooting.
It's mentioned where the ICM controls spark at cranking and below 400rpm. I assume it controls the injectors as well.
I have spark, obviously it starts on starting fluid. But I did verify spark.
My thought is that it is still able to control spark. But not fuel until it hits 400rpms. when starting fluid initializes the cranking, it exceeds 400rpm and the ECM takes over fuel control.
But the new ICM acts just like the previous 3. The previous owner obviously went down the route of trying the ICM because there was an extra ICM and an extra with coils.
I do believe he changed the CAM sensor because I have the old one in the box of extra parts. But I don't think he actually changed the crank sensor. if he did, it looks like it's been on the engine awhile and I can't imagine putting in a used crank sensor when a new one is Delco one $30. Plus it doesn't look as easy as the cam sensor since you have to pull the balancer.
Sounds like an issue with the bypass circuit (tan/black # 424) to me. Try to back probe that terminal at the ICM connector and connect it to ground. If it starts, remove the jumper from ground and connect to your meter to see if you have 5V . If not, you are running at base timing. I'm not sure if the bypass circuit in the ICM is Hi z or not but, if it is a lack of a 0v there when cranking, that could do it. If you see 5v running and more than 0v cranking, I would suspect the ecm.
Yes I have. I'm using his for my LS4 swap tuning as well.
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Originally posted by OldsFiero:
Sounds like an issue with the bypass circuit (tan/black # 424) to me. Try to back probe that terminal at the ICM connector and connect it to ground. If it starts, remove the jumper from ground and connect to your meter to see if you have 5V . If not, you are running at base timing. I'm not sure if the bypass circuit in the ICM is Hi z or not but, if it is a lack of a 0v there when cranking, that could do it. If you see 5v running and more than 0v cranking, I would suspect the ecm.
I did contact Ryan Gick. He said that to measure the voltage on the injector pin, it needs to have a load and it should have 12V on each pin. I verified this by measure with the injector plugged in and inserting pins on the connector to make contact.
12v on each injector connector pin.
on the cam and crank sensor, I get 6.7V on pin G/H/J of the ICM. This was what I expected. Approx 7V.
I see 11V on pin N of the ICM, sensor feed out. Should be 10-12V
12V, battery voltage on pin P of the ICM.
I attempted grounding the Bypass Pin B of the ICM and starting the car. It would not start.
I started the car with starting fluid. Then grounded the bypass and could hear the timing change. I have a OBD II scan tool app on my phone. I can monitor timing. It dropped from 24 deg to 19-20 deg.
Upon stopping the car, and restarting, it stayed in bypass mode and the observed timing was 10.0 deg. But I was able to start the car the car without starting fluid.
I did not see any voltage on the bypass circuit. The car would not come out of bypass. So by removing the circuit from ground, timing stayed at 10deg.
I had to turn the ignition off for a decent amount of time to get it out of bypass. 5 seconds or less was not enough time. It stayed in bypass.
After it came out of bypass, it could not get it to repeat by grounding the bypass circuit. But it would also not start again with the timing at the original 24degrees. Now it's stuck on 19-20degrees.
It's possible I damaged something. But I'm clueless at this point. I have a general grasp of how the ignition system works.
I'm seeing 4.5-5v average on the 3x signal and less than 3v avg on the 18x. Where it should be appox 5.5v and 4.5v respectively.
I need to recheck these voltages. I thought I was dropping voltage in the harness from the ICM, through the sensor, and back to the ICM, but I'm seeing what I think it should be, 10V input and 7V output. And each of the 3 circuits are seeing the same 6.7V. That's with the engine off of course. The interrupter ring turns the 7V on-off-on-off... reducing the average voltage for the 360 degree rotation. Seen as a square waves.
I ordered a cheap handheld digital O-scope. It was $40 on amazon so I'll be able to freeze the signal and look at it better. Maybe something is off that I can't see on my old oscope.
I only get about an hour in the evenings if I'm not already exhausted from work and life.
Wiring problems? (Lots of continuity checking!) If not, then which PCM are you running? I've had a '95 PCM go compleatly bonkers! I changed and repinned for a later '98+ PCM. No more problems afterwards😉
It's a '98+ PCM. I'm not ruling out a wiring issue. But I've check continuity on any circuits I think could be related and then some more. I could have a short between circuits, But that's something I'll check if I have to pull the drivetrain before getting it running right. It's coming out for a clutch anyway.
I don't think grounding the bypass circuit would cause damage, but that's not to say you don't have a problem with the board. Another thought; have you checked supply voltages at the PCM while cranking? Might want to headlight bulb test powers and grounds at the PCM connector, if you haven't already.
I see that it's a manual trans. Just for grins try shutting the car off on a grade where it will roll and try pop starting it.
I don't think grounding the bypass circuit would cause damage, but that's not to say you don't have a problem with the board. Another thought; have you checked supply voltages at the PCM while cranking? Might want to headlight bulb test powers and grounds at the PCM connector, if you haven't already.
I see that it's a manual trans. Just for grins try shutting the car off on a grade where it will roll and try pop starting it.
Marc
I live in FL we don't have grades. But I did kill the engine, then roll start it several times. I bought HPTuners as well for the VCM scanner(among other things) While roll starting the car, I still need to see over 800rpm before the injectors pulse. Cranking with the starter only sees about 200rpm. While cranking, I'm seeing just over 11v at the PCM battery power and slightly lower at the PCM hot in run pin. I don't think it's a battery voltage issue.
Tomorrow I'm going to start pulling the drivetrain for the clutch swap. So I'll be able to inspect everything and button up a few things I don't like about how the swap was done. I can also do continuity checks on all the PCM connections.
I think it's a MAP issue. I noticed on VCM scan that my MAP reading was maxed at 200kPa. I unplugged the MAP and it fired up, albeit with a CEL for the MAP sensor. it's after dark now so I'll checkout the wiring in the morning, otherwise I'll be getting a new MAP.
Thanks for everyone who helped. I'll update the post with the final result, but I'm 90% there.
Ryan GMTuners is awesome for anyone that didn't already know. He's help this community for decades. I'm sure I'm not the first person he's spent time giving free help to.
