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Brain storming (engine randomly dies)

Just to keep going on this, spent a bit of time the other day looking underhood while it idled (15 minutes plus with no hiccups, go figure), and noticed that the bracket for a few of the relays had come loose and was laying on the steering shaft. It holds the ESC module, MAF relay, and MAF burnoff relay.

As always, too dark to look at it closely, but the wiring was pretty taught, but didn't appear to have rubbed the wires bare. Needs a very good inspection though. Can't even remember how the bracket was attached, but I know it was connected to the brake booster somehow, I'll make something better and be sure to use locking nuts or loc-tite. Also noticed it won't run nor start with the fuel pump relay disconnected, so something is wrong with the fuel pump circuit, no idea if related.
 
FWIW, when I burn a new chip incorrectly (or put it in backwards) the CEL will flicker like that when I turn on the key. That what I was going to guess until you said you swapped computers and the problem was still there.
 
bp71k5 said:
FWIW, when I burn a new chip incorrectly (or put it in backwards) the CEL will flicker like that when I turn on the key. That what I was going to guess until you said you swapped computers and the problem was still there.
Click to expand...

Yes, although I suppose I could burn a new PROM. In the past for instance, due to a bug(?) I lost deceleration fuel cutoff. Never really noticed until I got into steep downhills and noticed compression braking really wasn't effective. It was 100% repeatable however, but never know. I did run it off the emulator as well, but without a "new" bin, doesn't mean I've eliminated the issue, if there is one in the bin.
 
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Is it flickering like it was before you added the 10k Ω resistor to the LED you’re using for the CEL?
 
rampage said:
Is it flickering like it was before you added the 10k Ω resistor to the LED you’re using for the CEL?
Click to expand...

No, and that had crossed my mind.

But, having said that, my theory as to why that isn't what is going on (which is just a theory, not fact lol):

I am multiple years into the LED/resistor swap and the problem hasn't manifested in the past. Granted, that doesn't mean it didn't decide to fail.
If the vehicle is operating correctly, the LED never flickers (when lit of course) that I've ever seen. This would be a very improbable coincidence otherwise.
The light works properly (illuminates and stays lit, does not flicker) as soon as the poor running starts to manifest itself. Flickering only seems to happen after the engine stalls and light has been on for a bit. I've only had it fail once where I could really pay attention to it, so it doesn't necessarily happen every time, I don't have a bunch of occurrences to draw a conclusion from.
If I reset the ECM, and turn key to run without starting it, the CEL stays on solid and bright as long as I leave the key in that position.
The light is grounded through the ECM...I can't see how an issue with the CEL LED would cause the vehicle to run poorly.

My thinking could be flawed, what I was hoping to happen was to have the CEL start flickering, so I could start messing with connections and what not to see if I can affect how the flicker. I'm open to critique of my thought process. :)
 
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I would go with ignition problem because you posted that the engine was mis-firing. A fuel problem would cause it to run poorly, and possibly back fire, but not mis-fire. A mis-fire is going to start at the distributor or coil more likely than any where else down the line in an ignition system. Especially when it is a random problem.
 
I'm going to check the coil properly next time this occurs. I may swap it as well, but unfortunately thus far that wont let me know its fixed as it seems to start ok after the stall sometimes.
 
Modified the bracket I had used in the past. Somehow the old one broke, which is what I mentioned prior. It (and the relays/ESC module attached) were laying on the steering shaft.

I grabbed the ABS bracket off either an R/V or C/K long ago, but I hadn't modified it, just bolted other brackets to it. I'm not doing this again, so I cut it off square, and welded some leftover thick angle iron to it, and used another piece to square it off on the backside. A bit wider than necessary, but doesn't interfere with anything. Gap between the single relay and the others is to clear the brake line coils.

Relays are fuel pump (also rewired from odd TPI square relay to more common oval relay), MAF burnoff, MAF, and then the ESC module on the back.



I decided to test the fuel pump oil pressure switch, and the truck won't start nor run with the relay disconnected. That means something is wrong with the switch or wiring to it. I'm *hoping* that because the wiring at the relays was pulled so tight due to the broken bracket, under certain circumstances the fuel pump relay wasn't working properly because the electrical connection was broken. With the oil pressure switch also not working properly, that would have starved the engine for fuel.

Still think that theory is a bit of a stretch based on how it would run, poorly, but now that I've found an issue with the fuel pump switch, I'm optimistic. If nothing else, I'll fix a problem I wasn't aware of before.
 
If your engine will not run with the oil pressure sender switch disconnected than your engine is using that as the relay to run your fuel pumps, and not the fuel pump relay itself. If the fuel pump relay is working...you should be able to hear the relay contact clicking when you turn the key to the "RUN" position.

I am still thinking your trucks problem may be the ignition system. You might want to check the two little wires that come from the pick-up coil, and plug into the control module. Those two little wires are known for rubbing through on the body of the distributor and grounding out, or sometimes getting pinched under the pick-up coil.
 
Those pick up coil wires also can break under the insulation and only make a poor contact that can heat up and lose conductivity too..
This happens a lot on old HEI's with vacuum advance ,the wires flex each time the advance moves the base plate--but it can still happen on the newer ones too..some had solid conductor wire instead of stranded wire..
 
Yes, I can certainly check those as well. The TPI harness has a ton of wiring back there, and I guess due to the firewall design of the truck, the distributor wiring is shorter than it would be if I made the wiring. Plus the wiring just pops out of the large loom, and is really tough to clearly see, let alone access with the plenum and runners in the way.

Pump relay is working, it primes as it should, but I'll have to crawl under the truck to get at the switch/sender unit. Jumpering the switch wiring will quickly tell me if the issue is wiring or switch/sender. It's a new delco piece from 3 years back when I swapped the engine, so odd if it's the issue. But possible.
 
Woe is me lol. Some of this is just to maintain information so I don't forget.

Started truck up last night to move it, no issues. Parked it, noticed my backup camera was staying on even though it wasn't in reverse (runs off the reverse light switch on the 465, which I made a harness for) and when in reverse, the display was flickering/distorted. When I went back to check the (inappropriate for vehicular use) connectors near the back bumper the truck died like someone turned it off. I had JUST touched the wiring when it died, which made me think that was the cause somehow.

I turned the truck off, waited fifteen seconds, and turned it back to run. Check engine light did not flash (just on steady) and the fuel pump didn't run. And I heard a pretty loud buzzing sound from the engine bay. Quickly determined it was coming from a relay on the auxiliary fuse panel. Swapped with the relay right next to it, same noise. Started pulling fuses and the first one I pulled, the buzzing noise stopped. Replaced, noise back. Left fuse out, turned key off, waited, then back to run, and everything but the rear view camera worked properly, and truck started as it should.

I've got enough added wiring on this thing that it's apparent I need to create my own wiring diagram. This fuse I noted was for the rearview mirror/camera, but there is continuity to ground on one of the pins, and I'm going to have to spend some time figuring out how I wired up that circuit, because the back of the panel wiring doesn't look like I think it should...but these mini fuse panels are getting to be the size where it's hard to easily see what is what on the backside of them.
 
Thought I had resolved the issue with the backup camera fuse, but I was wrong. At least not fixed entirely.

Drove it the other day to get new tires, and it started to "flare" RPM's on startup when it was warm. Paying close attention, I noticed that the speedometer needle (electronic) was moving a bit, up to 2-3MPH or so, as I manipulated the throttle to increase RPM's. That made sense as to the "flare" on startup, as the manual trans tune has idle RPM increased when the vehicle is moving, to ease shifting.

Unplugging VSS stopped that from happening. Plugging it back in and disconnecting the DRAC (which converts the VSS signal and sends it to the speedometer, cruise, and ECM) also stopped the needle from moving.

Went in the garage and found another VSS. Pulled the one out of the truck, and compared the two. Hard to tell casually, but the length is different. The one I took out appears to have the little metal nub ground off. Perhaps (hopefully) from when the 241 front output was moving around, which I solved awhile back. Swapped the other VSS in, needle no longer moves.

Word of note, the VSS' I saw for the '90-91 applications are pricey IMO. $50 for the cheapest, up to almost $100 for AC Delco.
 
I believe you have a floating ground by the amount of weird electrical problems where things kind of work. You can test the theory using a bunch of alligator clip jumpers out of 10awg wire... but in reality I'd...

Make new ground wires. 1/0 from the battery to a new bolt on the the frame. 2awg from the same bolt on the frame to the body, preferably the cab, but the core support will work also. 2awg from the same bolt on the frame to the alternator bracket.
 
I recall a 90's Caddy we had sold at the junkyard as a repairable had a weird issue ,the engine would cut out or stall intermittently just cruising along,but the symptom could be induced by rolling down a power window or turning the headlamps on..usually the engine just stumbled and coughed and recovered and you could drive normally,but once in a while it'd just quit like you shut it off...

The former owner was so sick of getting it towed,he junked it!..

The customer who bought it was an experienced body man and had built and fixed cars a long time,but wasn't very "up" on newer cars with computers and EFI,he knew the common problems,but hadn't encountered one like this before..
He began swapping parts--tried another distributor,ECM,and that didn't change a thing..the problem seemed to vanish for awhile after each part was replaced and he thought it was fixed,then it'd act up again..sometimes it was days or a week before it acted up again..

One day a guy who works at a Chevy dealership (service manager) he spoke with said to inspect all the grounds for the ECM and other under dash wires,that usually are hooked to a bus bar type junction block on the passenger side foot well area...said they often corrode there badly..

He found all the wires were gangrene ,so was the junction block--he cut all the wires and stripped them back to good copper,and ground the paint off the inner kick panel and put all the wires on one large ring terminal and crimped and soldered them,and used a sheet metal screw and a star washer to the kick panel metal to ground them a few inches above the old junction block..

All the factory ground straps looked good and none were missing either,on the engine to body,transmission,etc..car was never molested,it was an elderly owner who originally had it..you could tell it was well maintained ,probably by a dealer..

The car ran great for about a week,but one day the guys wife had it and said when she turned on the A/C the engine felt like it stalled for a second,then came back to life..:doah:

He inspected all the wiring to the ECM and did find some that had either been "probed" with a test light,or scotchlocks were used to maybe install a car alarm (it had no evidence of one though)--or a rodent gnawed on the insulation,but none were broken completely,or had strands missing or corroded,so he just taped them up...

The car didn't act up again for a few weeks,then one day it died when he stepped on the brakes..he was able to get it to start again OK,but feared it'd keep doing it so he drove it home and parked it..

He added a separate ground wire right from the battery negative to the alternator case, and another wire to the ECM case and the car didn't act up again as long as he owned it,which was only a few months,he decided to get rid of it in case it started doing it again..
Electrical problems suck...they can defy the best troubleshooters and computer scanners when they are intermittent and dont eff up long enough to pinpoint the failing part..
 
I've got the components to make new cables, just hadn't been a priority, yet. Funny how as you dig into something, you start finding other things that need addressed...and there are a bunch.

Once I get the trailer done I'll hammer out new cables along with fixing the other known issues.

Additionally, I remembered how bad TPI runs without VSS...its entirely possible the way it stumbled and ran worse at low engine speeds was related, if the VSS was intermittent due to the sensor being damaged.

Edit: drove yesterday and today for a total of maybe 50 miles. Ran perfect yesterday, today on drive home check engine light came on and stayed on, but didn't run any different. Got home, checked code, 42. EST. Only way this code can be triggered is by the distributor module going bad (as far as I can tell, it means voltage on the bypass/timing wire, which goes direct from the ECM to module) but it's obviously intermittent, so who the hell knows. Or a loose memcal. Since I have the programmable chip in a ZIF, I'm starting to suspect this MAY be part of it. Going to have to research ways to make a more permanent connection. I hope this doesnt mean the end of my tuning equipment and money I invested in it. Although the chips are going the way of the dodo, doing away with them is the future I suppose.
 
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Long long long. Anyone that has followed along, figure I should close this out, as I think I got it.

While letting the truck sit and idle recently, I felt the urge to remove the fuel pump relay connector, letting the oil pressure switch run the pump. Disconnected, quickly stalled and died. Jumped the wires at the pressure switch, started and ran without issue.

Replaced the oil pressure switch, problem resolved.

Long story short, what I think happened, was that when the relay bracket fell off, it stretched the fuel pump relay wiring to the max, breaking contact, and the failing oil pressure switch caused it to eventually stall.

Having changed the relay out, "fixing" the wiring, and making sure the bracket is affixed permanently, I havent had a recurrence. Pretty confident I got it, as the pressure switch was definitely faulty.
 
dyeager535 said:
Long long long. Anyone that has followed along, figure I should close this out, as I think I got it.

While letting the truck sit and idle recently, I felt the urge to remove the fuel pump relay connector, letting the oil pressure switch run the pump. Disconnected, quickly stalled and died. Jumped the wires at the pressure switch, started and ran without issue.

Replaced the oil pressure switch, problem resolved.

Long story short, what I think happened, was that when the relay bracket fell off, it stretched the fuel pump relay wiring to the max, breaking contact, and the failing oil pressure switch caused it to eventually stall.

Having changed the relay out, "fixing" the wiring, and making sure the bracket is affixed permanently, I havent had a recurrence. Pretty confident I got it, as the pressure switch was definitely faulty.
Click to expand...

So, you are saying that your injectors where running off the oil pressure switch, and not the injector relay. I extended the wires on my oil pressure switch because GM made them too short. I also used some brass fittings to relocate the oil pressure switch to a more open area of the firewall, and there is also a plugged port in the brass fittings I can use to install a mechanical oil pressure gauge if I needed to.
 
1-ton said:
So, you are saying that your injectors where running off the oil pressure switch, and not the injector relay.
Click to expand...

Exactly. And if the relay is out of the picture, a failed oil pressure switch leaves you stranded.

I'm a bit confused as to why the pressure switch failed, it's a Delco piece, and very, very few miles or years on it. This is one of the three wire sender/switch combos (instead of the earlier separate oil pressure switch and sender) but the oil pressure reading never faltered or I would have had a better clue. I'm running it above the oil filter as TPI obstructs the spot next to the distributor.
 
I remember lying under my sisters Vega years ago to drop the fuel tank no less than 2 times,to replace the oem electric fuel pump--it ran great until the next day ,on her way to work it died again..
Assumed the "new" fuel pump was defective,so I yanked it back out (in 30 degree slushy weather!) and installed another Airtex new pump--it ran fine after that until about a week later,when it died again with the same symptoms..
I learned upon further investigation and asking other GM mechanics what else could cause that---they said the oil pressure switch also had contacts to run the fuel pump,if the engine lost oil pressure,it would shut down the fuel pump..:doah:..only the portion of the oil pressure switch that had to do with the fuel pump was faulty,the oil light worked normally ,and the engine had good oil pressure..a new switch cured it..
 
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