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I lost starting and cranking in rapid succession on my 1989 5.7 TPI, and I'm looking for help with its diagnosis.
I just put the TPI system back together after resolving a coolant leak between the plenum and head, fired the engine back up, and it started running nicely. Had it going for about a minute, noticed a drip coming from a heater hose, so I shut it off, tightened the hose clamp, and gave it a close inspection for more leaks but didn't find any. I may have added some coolant to the radiator at this point and splashed a small amount of coolant on some sketchy wiring near the battery, but it didn't seem like a big deal. Could be wrong about that.
When I went to restart the engine, I wasn't getting the SES light anymore, but my Security light would still come on and the car would crank over but not start. Shortly after, I lost the Security light as well, and the car would no longer crank over.
I've checked all the fuses in the fuse block, convenience panel, and the one in front of the battery. They're all good, and I'm getting 12v at the one in front of the battery. I am also getting 12v in the start position at the VATS relay in the driver's kick panel, and can spin the starter at good speed when I bypass the relay. It sorta seems like my ECM isn't turning on at all, has this situation happened to anyone else?
I'm going to check for power to the ECM next. Would the fusible links be suspect if I can still activate the starter with VATS bypassed?
- getting 12v to yellow wire in start at starter enable relay
- starter does work at 12.5v when relay is bypassed and key is turned to start position
- getting 12v to both battery pins of ecm. ecm does not show signs of corrosion.
-charged battery to full on a trickle charger to eliminate weak battery possibility.
-orange wire weatherpack connection near battery was badly frayed, fell apart when moved. Replaced with shielded spade connectors since that's what I had, should be ok in the short term.
-dropped the steering column to gain access to ignition switch. According to this: https://www.thirdgen.org/forums/elec...ml#post2570704
I should be getting 12v at the start position on the yellow wire at the ignition switch, but I am not. Yellow wire has been hacked up, somebody has been in here before. There's like a smaller yellow wire coming out of the same bundle that goes into the ignition switch that has been electrical taped to a red wire. smh.
All signs are pointing to fusible link meltage in the starter area, which I have avoided since I don't like jacking cars up on gravel. Looks like it's time to get sketchy.
Here's what I've confirmed so far:
All signs are pointing to fusible link meltage in the starter area, which I have avoided since I don't like jacking cars up on gravel. Looks like it's time to get sketchy.
I would agree that jacking a vehicle on a gravel (or even asphalt) surface without proper equipment and portable bases is not safe.
- getting 12v to yellow wire in start at starter enable relay
The presence of 12V with the switch in the START position would seem to eliminate one fusible link as a suspect. If you temporarily ground the dark green (or possibly BLK-YEL) wire at the starter enable relay, does the starter operate with the ignition switch? If so, that would eliminate TWO fusible links as causes. That would also eliminate the neutral safety/clutch swich and starter/solenoid assembly.
I should be getting 12v at the start position on the yellow wire at the ignition switch, but I am not.
This seems to contradict the previous statement, since that yellow wire should be also connected at the start enable relay. Can you operate the ignition switch by hand, right at the column, instead of via the ignition lock cylinder? It is not uncommon for the linkage to wear and prevent full actuation of the column-mounted ignition switch. Usually the link rod can be moved by hand once the switch is exposed to actuate the switch.
There's like a smaller yellow wire coming out of the same bundle that goes into the ignition switch that has been electrical taped to a red wire.
That is potential evidence of a previous installatrion of a remote start system, added vehicle alarm, or some prior attampt at repairs.
This seems to contradict the previous statement, since that yellow wire should be also connected at the start enable relay. Can you operate the ignition switch by hand, right at the column, instead of via the ignition lock cylinder? It is not uncommon for the linkage to wear and prevent full actuation of the column-mounted ignition switch. Usually the link rod can be moved by hand once the switch is exposed to actuate the switch.
I re-probed the wire with the key in start, and I am actually getting +12 at the yellow wire from the ignition switch. I can help move the rod but not without gentle assistance from the key as well. It's very rusty but not loose, some gentle wiggling in any direction didn't seem to have any effect.
Originally Posted by Vader
The presence of 12V with the switch in the START position would seem to eliminate one fusible link as a suspect. If you temporarily ground the dark green (or possibly BLK-YEL) wire at the starter enable relay, does the starter operate with the ignition switch? If so, that would eliminate TWO fusible links as causes. That would also eliminate the neutral safety/clutch swich and starter/solenoid assembly.
If I temporarily ground the dark green wire at the starter enable relay, the starter does operate with the ignition switch. I redid this test:
1.) Put a meter between ground and the yellow wire at the ignition harness. Turn the key to START. You should have +12V. If so, go to step #2. If not, check the fusible link back to the battery for an open connection. - I do have +12v in start.
2.) Probe the starter enable relay terminals C & E for +12V when the key is in START. If so, go to the next step, if not, you've got a break between the ignition switch and the relay. - I do have +12v on both yellow wires ( C & E ) with the key in start.
3.) Probe terminal A on the enable relay and turn the key. If you don't have +12V, then most likely it's a VATS issue and you can test this by grounding terminal B and trying again. If you get +12V now, it's a VATS problem. If you do not, then the enable relay is toasted. If you did get +12V go to step #4. - I do not have +12v at terminal A (GRN / WHT). I then grounded terminal B (GRN), and the starter engaged with the key in start so that's a pretty clear indicator of +12v at terminal A.
Looks like it's a VATS problem then, certainly a non-functional VATS module would cause no security light.
Sounds like you found the problem. But if you have a hz setting on your vom can turn the key and watch the hz at pin b6 of the ecm dark blue wire should be 30hz at 50-60%.
Sounds like you found the problem. But if you have a hz setting on your vom can turn the key and watch the hz at pin b6 of the ecm dark blue wire should be 30hz at 50-60%.
I don't have duty cycle on my vom, but I was getting 776hz at pin b6 with the key on.
It took a week for the bypass relay to arrive, I installed it today and there's no change in the car's behavior. Turns over with the start enable relay bypassed, no security light, no SES light, no attempt at spark.
I installed it with default settings, should be 50hz. The led on the bypass module is blinking so I'm pretty sure it's installed correctly, I used the radio power and ground since the radio wasn't working anyway. I haven't tried the alternate duty cycle 50hz that it can output. I spliced it into the blue wire on B6 from this pinout reference: https://j.b5z.net/i/u/2098530/i/1227...Pinout_ezr.JPG
I can hear the fuel pump activating. The 20a fuse in the engine compartment was fine, tried switching it for another new one just in case, didn't do anything. At this point I'm starting to suspect it's a no spark issue, I'll test the ICM and coil and see what happens there. Originally I ruled these out because I wasn't getting the SES light, you'd think I'd simply be able to get a code from the ECM if it were one of those things. When the car is cranking, the water temp gauge maxes out, the voltmeter doesn't respond, and the oil pressure gauge doesn't respond. Oil pressure gauge used to swing all the way up and max out, then died, but I'm pretty sure I had it running for a couple times while it was dead. If my oil pressure sensor was toast, would it cause the symptoms I'm seeing? I guess the ECM could also simply have gone bad, when I opened it up there didn't appear to be any corrosion on the circuit board.
I may be wrong, so don't quote me. But I believe the car won't start if it's not registering any oil pressure.
Quoted! I have read this as well, but I'm able to get the engine running in its current state so either the connection between the oil pressure sensor and the gauge is messed up, or it's possible to start an '89 L98 car without it.
I switched the bypass to 30hz today and was successful in achieving a running engine. It was running pretty poorly, shaking around but did hold an idle and could be revved somewhat. No tach, no voltmeter, no oil pressure gauge, still no security or SES light, but it ran. I let it do its thing for a minute and it sorta smoothed out a little, then I shut it off.
Went to turn it back on, and it just cranked. I noticed the flashing LED on my bypass box wasn't working, tested the voltage and wasn't getting much. Wired it directly to the 12v always on going to the radio and got blinks again, so something is funky with the switched 12v going to the radio. Battery voltage tested at 12.3v in the car, sorta low. I'm going to charge the battery back to full and rewire the bypass box to the yellow wire hanging out of the ignition switch, and ground it directly to the frame.
Not sure why it was running poorly. I've had cars with dead alternators run like that, maybe it fried after the reinstall. I suppose it could have taken out the ecm as well, and I was actually running on the memcal?
The stock installaton does not require the oil pressure switch to sense pressure to run the engine. That's what the fuel pump relay is for. The oil pressure switch also does not tie into the spark control or security systems.
Rewired the bypass box today, I was consistently able to get it started and running several times. It was running poorly, like it had a lumpy cam. I was getting 14v at the battery while it was running and 12.7v when it was off, seems like the alternator is working.
I jiggled all the wiring inside the engine bay, and now it won't start again. The temperature gauge is maxed out, it used to max out when the car was cranking and now it just stays maxed out. I'm guessing there's some kind of short somewhere?
Still have no security or SES light. When I jump terminals A and B on my ALDL connector one of my fans starts spinning.
The no start sounds like a open not a short. Check for basics spark and injector pulse and fuel pressure.
might be a issue by the distributor since the wires get rather hot there.
I examined each wired connector and carefully jostled wires around to seemingly optimal places, and I'm back to running poorly with a few new symptoms:
-Brights and fog lights are dimly illuminated when the engine is running. They are not on with key off, or key on engine off.
-Oil pressure gauge came back. Reads kinda low, doesn't respond to rpm very much.
-Water temp gauge came back. Assuming it's working, I shut the car off at around 240 degrees.
-Blower motor is no longer responding.
-Hissing coming from HVAC panel
So I'm calling it a mission failed successfully for today. Wiring sketchiness level: maximum.
I've made some progress. I did some diagnostics, and it turns out I'm not getting any dash lights whatsoever, so it's not just an issue with the Security and SES light. Considering several gauges are also out / intermittent, I think that's a separate issue that I still haven't gotten to the bottom of, but not related to how the engine was running.
I replaced the negative battery cable with a new AC Delco unit and cleaned the battery to head and battery to body grounds. The terminal sheath had been rubbed away and there was extreme teal corrosion on the wires, so this wasn't helping my problem. I think the blower fan has worked since I did this, so that's one direction in the positive. This didn't really fix any of my primary issues, but it was a good idea and very easy to do with the smog pump removed.
I dropped the fuse box panel down and had a look at the back side where the wires connect:
I picked out the large chunks, then hit it with a vaccuum / compressed air combo and finally hosed it down in crc electrical cleaner (battery disconnected!) and let it dry.
I reconnected the battery, tried a crank, and got no fuel pump. Did kind of a squeezy grip on the fuses and wires and the fuel pump came back online and it fired up running excellent. Probably going to pull the cluster and check for further horrors, but I also need to retest all my connections now that there's a better chance electricity flows in and out of the fusebox.
I wanted to follow up on this since I've gotten the rest of it sorted out for anyone who arrives here in the future with a similar issue. Poor grounds, shoddy wiring in multiple places, a blown fan resistor pack, and a heavily corroded instrument cluster circuit board were causing my issues. The grounding issue got worse as the temperature outside increased and dried out the car. Basically there wasn't enough juice reaching the VATS module and cluster.
After chopping out / replacing the bad wires (mostly in the engine cooling fan harness, an unrelated but high amp draw part of the system), cleaning up all my grounds, replacing the fan resistor pack and cluster circuit board, I have all lights and gauges functional. Car is still running strong as well.
My overall advice is to inspect the entire electrical harness front to back, and clean up anything you find that doesn't look right. Return the wiring to factory spec, or improve it where the factory cheaped out. Heatshrink every butt connector, repair weatherpack connectors using the right tools. Eventually all the little fixes will add up.
04-21-2021, 03:43 PM
I have read this as well, but I'm able to get the engine running in its current state so either the connection between the oil pressure sensor and the gauge is messed up, or it's possible to start an '89 L98 car without it.
