Brain storming (engine randomly dies)

[dyeager535]

I don't mind folks throwing out ideas and past experiences. This may be hard to resolve because it's so far very intermittent. Plus, who has time to randomly get stranded? It's not like I drive just to drive and am ok with a dead truck 30 miles from the house.

Anyway...truck stranded me about a month back.

Back story: Truck sat from November to February. First time I drove it again, ran fine for the first 30 minutes. Parked it, let it sit an hour, fired it up, went to drive down the road and it started misfiring. Any time I started to give it gas, it would start bucking like it was starving for fuel. Had an old carb that felt similar. Figured sitting that long perhaps the gas was going bad, so drove straight to nearest station and dumped a few gallons of 92 octane in it. Started driving it, within a few seconds the problem cleared up. Success!

Drove it for about five hours, seemingly ran like a champ. Took a break from driving, started up a few hours later and kept going. Fuel consumption kind of surprised me. Economy had really taken a hit...like 13 instead of 16. Enough that I wondered whether I'd make the next station. Made it to a station, filled up with fuel, and started on my way again. Cruising at 65MPH, less than 15 minutes after filling up, flat ground, check engine light comes on and almost immediately the truck starts to buck, and no matter what I do I can't maintain speed. Luckily there is an offramp right there, and I coast off the freeway. Truck is idling, roughly, but continues to idle. Try to get through the intersection but even letting the clutch out in low/4 low makes it want to stall, and eventually it does. At that point it won't restart. I fiddled around with some connectors just to make sure something I could easily reach wasn't loose, and the check engine only flashed code 12. One oddity I witnessed was that the check engine light seemed to act abnormally at times...such as being dim. But again, seemed random. Disconnect ECM, reconnect, check engine light acted ok. Crank the engine, check engine light comes on, code 12. Repeated a few times.

After I get it towed and stored, I call the tow yard guy a couple weeks later. He mentions they had to move it, and it started right up and moved without issue. Two weeks after that, it started right up again to load on a trailer. Since then it has started and run fine, but only for very short periods of time, I don't trust it enough to drive.

For those not familiar, it's an L31 crate engine, MAF TPI, manual trans. That I think pertinent off the top of my head, the fuel pump is new within the last few years (Delco) so the hose should be ethanol rated. The pickup coil and ignition module are both a few years old, both parts store brands replaced when the OEM pickup coil failed.

I was unable to test the fuel pressure or for spark when it "died". I regret not immediately checking spark.

My first thought is ignition module. Code 12 being set may indicate no pulse from the ignition module. But that's a bit odd since it ran even with the check engine light on, at least for awhile. It seems unlikely to me that anything on the fuel side could be intermittent like this. I can see a bad connector, ground, or wire potentially, but just from sitting, no movement, and then it works like nothing is wrong, seems unlikely.

I can throw parts at it, I've got spares of just about everything, but I hate not knowing whether or not I got the culprit...because then I'm not going to trust it. And I really don't want to have to carry around a crate of spare parts lol. Just figured I'd spew this, and see what others have experienced that may have been similar.

 

[rampage]

Possibly a wire shorting out when you hit a bump. Where was the truck sitting from Nov through Feb? Any chance a rodent chewed the insulation off some wires?

 

[diesel4me]

I've had a few ignition coils crap out after the engine was run awhile,they heated up and shorted out internally,but "recovered" and seemed fine again--till the next time..had a pick up coil in an HEI do the same thing too..
Ignition modules can "come and go" intermittently too..
The check engine light may not set a code for either of those failures..

 

[dyeager535]

Possibly a wire shorting out when you hit a bump. Where was the truck sitting from Nov through Feb? Any chance a rodent chewed the insulation off some wires?

Just sitting in my yard, and I'm rural lol. It is entirely possible a rodent got in there. Amazingly/luckily thus far in ~10 years out here, I've not had issues with wires being chewed, but it is definitely a possibility. I have considered that. My engine bay is pretty darn bare, as is the cab, so there isn't much for hiding places, but it's something I will check. One reason I did a cursory check of the wiring, but that was only what I could see. I didn't crawl under the truck, nor could I see all of the wiring around the intake/runners.

 

[dyeager535]

I've had a few ignition coils crap out after the engine was run awhile,they heated up and shorted out internally,but "recovered" and seemed fine again

Have you ever had one cause the vehicle to run, but run poorly? That's the only iffy part for me. I *think* the ignition coil is OEM. I know you can test it, but wonder what the results will be when the vehicle runs fine? It appears the coil tests are pass/fail. Valid when it's not running, perhaps not so when it seems to work properly. I have a meter in my toolbox now (coil failure taught me to carry a cheapy) so as long as I have the test procedures, guess it wouldn't be tough to check if failure happens down the road.

 

[diesel4me]

I had one old chevy with points that had a dying coil--car always started up and ran "ok",but lacked power and sometimes would not want to accelerate,like it had a plugged fuel filter--then all of a sudden it would come to life again and take off,then go back to running like it had no balls..

I put another used coil on it and the difference was amazing..felt like I added 75 HP..evidently the original one had a internal short in the windings that made contact most of the time,which greatly reduced its output voltage,and once in a while it would lose contact and deliver full voltage temporarily..

I had a pick up coil in an HEI do much the same thing,the engine lacked power,felt "flat" when you booted it..then it might "catch" and take off like it should,then go back to the bogging "no power" mode..eventually it stalled one day and refused to start up again..

I put another distributor I had in it and it was like a new engine--did some tests on the old one and the pick up coil was not showing the correct ohms when I tested it going by the motor's manual..
I put a new one in it,used the distributor in another engine and it ran fine,so I assume that was the culprit..

One time I had a HEI with a "E-Tron" ignition module and the truck never seemed to have the power it should have,despite having good compression,etc..
I had read in a Standard Blue Streak catalog at work, many "cheap" aftermarket ignition modules lacked a dwell advance circuit,so for the hell of it I put in an OEM Ac-Delco one I had kicking around..
The engine felt like it gained a lot of power at low and mid range rpms..so I assumed the E-tron module had no dwell advance circuit..

GM had a recall on some later 80's HEI's--my brothers '86 Monte Carlo SS was on the list,so he took it to the dealer--it turned out some of them had the wrong pick up coil and or ignition coil installed at the factory--the ones intended for an Olds or Pontiac ,have the rotation of the distributor in the opposite direction than a chevy,and the pick up coil and ignition coil are wound internally "reversed",so the polarity is correct..

GM color coded the ignition coil with a dot of paint on the distrubutor cap and the ignition coil had different colored wires,to identify which was which..(I think white and red .I'm not sure now it's been so long),and the pick up coil had different colored wires..the engine will still run with mis-matched components,but the spark intensity is greatly reduced if the polarity is wrong..
Evidently GM substituted some coils and pick ups intended for Olds or Pontiacs in some Chevys..my brothers 305 ran noticeably better after the right parts were installed..

Issues like this are why I dislike computers,sensors,even HEI or electronic ignition isn't my favorite--there are so many components that can cause the same issues and not always do it continuously ,these intermittent failures that set no codes are what drive mechanics nuts..a micro-chip has a temporary malfunction and the vehicle dies,and it might come back to life and run great for days again..makes it difficult to pin down exactly what the cause was..

 

[swettysblazer]

I've been having issues with a funky oil pressure switch or the wiring going to it. It was cutting the fuel and the truck wouldn't start or it would just randomly shut off. Maybe check that and see where you're at as that's tied in directly to the fuel pump circuit.

 

[ZooMad75]

I think the heat of driving is the clue. I've seen coils quit when they get hot, cool off and they work fine. Same thing for the fuel pump. The pump could be getting hot and quitting, comes back when it cools off. Simple checks for either. Run it until it gets hot, when the issue comes on check the fuel pressure. If the pressure is steady and in spec, then look at the spark.

 

[imiceman44]

I think it's possible that the fuel is the issue, but I think most likely a spark issue and my bet is on ignition module but the coil is a close second.
I have had both happen and the coil was more repeatable than the ignition module which happened randomly.

 

[muddermilitia]

Have you ever had one cause the vehicle to run, but run poorly? That's the only iffy part for me. I *think* the ignition coil is OEM. I know you can test it, but wonder what the results will be when the vehicle runs fine? It appears the coil tests are pass/fail. Valid when it's not running, perhaps not so when it seems to work properly. I have a meter in my toolbox now (coil failure taught me to carry a cheapy) so as long as I have the test procedures, guess it wouldn't be tough to check if failure happens down the road.

Yes. Now keep in mind this is on my 1952 Dodge with a flathead 6, carburetor, 6 volt electrical, Pertronix electronic ignition, and a newer NAPA coil.

Drove it like 80 miles for a car show. Get a block away and it started doing what you were describing. I couldn't get the car faster than like 20mph or it would die out for good. Seemed to idle just fine. Friends at the show were helping me out. Everyone was pushing me towards fuel problems, I thought it was ignition. Stupidly, I listened to them. I swapped on a spare carb I carry. Didn't change anything. Had it towed home. Next day it ran to the store just fine. On the way back it acted up again. With straight pipe exhaust and a 6 cylinder, it sounded like I was shooting a machine gun going down the road.

Replace the coil the next day and it was just fine

 

[diesel4me]

A dying condensor can cause the same symptoms--poor power,backfiring,and stalling--then come back to life if it feels like it and let the engine run great again..
The condensor on point ignitions is what allows the coil to have its magnetic field in the primary windings collapse quickly enough to induce the secondary windings to make a high voltage low amperage spark jump the gap at the plugs..also prevents arcing across the point contacts..

I've had them drive me nuts on small engines,especially Tecumseh's,they seem to have the crappiest condensors and the Briggs & Startton ones with one point contact made into the condensor are a close second.

They are buried under the flywheel too,and one day the engine may run great--the next it may not start,or start,but die the minute you put any load on it..the spark doesn't always look weak or yellow when one fails either,it can still look like nice healthy blue spark,but it has no "heat" to it..
An old timer showed me a crude way to test the spark intensity--put a sheet of paper between the plug wire and ground and crank it over--if the spark will "punch" thru the paper and jump the gap,leaving little black pinholes,it is strong enough to fire a plug under compression..
That test probably wont apply to an HEI coil,even a dying one of those would probably still punch holes in the paper..
I found out the hard way on HEI's if you check for spark by pulling a plug wire off and hold it away from ground and crank it--it'll jump as far as an inch or more--and that wide a gap can "pop" the module!..your supposed to put a spark plug on the wire or a spark tester ,not let it jump thru air a long distance..

 

[RubberFloorMat]

Obviously just a guess but I had a coil do the exact same thing as you describe. It would go from perfect to weak spark to no spark and then back to perfect spark.

Now this was on a ford but that’s somewhat irrelevant.

I would do typical diagnosis stuff and eliminate items one by one but it sounds like ignition, coil etc.

 

[dyeager535]

I think the heat of driving is the clue. I've seen coils quit when they get hot, cool off and they work fine. Same thing for the fuel pump. The pump could be getting hot and quitting, comes back when it cools off. Simple checks for either. Run it until it gets hot, when the issue comes on check the fuel pressure. If the pressure is steady and in spec, then look at the spark.

Thus far I haven't been able to replicate it, if it was frequent I'd be all over it. Issue for me is when to drive the thing that DOESN'T make me late for work or in the dark if it decides to fail. Not to mention the safety issues, where I live and work there are no/very small shoulders but plenty of traffic moving 35-50MPH.

Swapping coil out is pretty easy on this thing, the module is a PITA.

I'm leaning towards ignition more than fuel, but I will do the right thing and inspect as best I can first. Spark is a heck of a lot easier to check than fuel in any case.

Both times it acted up after what could be considered heat soak (parked for 30 minutes or so, and stopping for gas for 10-15 minutes), so perhaps as the weather warms up it will be easier to replicate. Both times temp was in the 30's.

 

[diesel4me]

Electronic components can be flukey with temperature swings...

My friend had a Dodge Dakota come in his shop (on a ramp truck) --it refused to start--this was in the winter,it was about 30 degrees out.....it cranked over good,even had spark showing when he pulled a plug wire and had me turn the key and crank it..
It refused to fire even with starting fluid..

After the truck sat in his heated bay all morning and we checked fuses,the fuel pump pressure and looked for any obvious defects and saw no broken wires,etc,he decided he'd have to work at diagnosing it later,he had other cars lined up outside needing brakes,exhaust,etc..

I sat in the truck so he could push it out while I steered--but for the heck of it I tried cranking it--it fired right up instantly !..ran normal too!--he gets in and drives it around the block,then parked it outside..

After he was done doing the other cars,he went to drive the Dakota back in--once again,all it'd do was crank over,but not fire up..we ended up pushing it in the shop with my truck..

He's usually good at figuring out weird electrical gremlins,but this one had him puzzled..then he said "I just remembered something"..

He went to his tool box and got out a heat gun,and plugged it in and pointed it at the computer,which was mounted on the inner fender under the hood..let it blow on it a few minutes,then he said "ok,get in and see if it'll start..it fired right up!..

" I remember another Dodge that did this like 15 years ago--and it was some chip in the ECM I guess didn't like the cold "..

Next morning the shop was back down to outside temperature (about 20 degrees),and it refused to fire again until he used the heat gun on it again...told the customer ,who had been calling every hour asking "is it fixed yet"? ,that it needs a computer.."but I NEED the truck to get to work,and my wife to work--can you get one by tomorrow?"--

I'll have to search boneyards for one,I doubt anyone has one of these on the shelf at a parts store,and it'll be $100 if they did at least probably"...
"How do you know its the computer" ?..

" I can get it running by warming it up with my heat gun--has this just started happening since it got cold out" ?..

"Um yeah,it just started doing it a week ago--sometimes it did start after cranking it a lot,once it ran and warmed up,it never died on me driving it--only after it sits in the parking lot at work and cools off does it not start"..

The customer shows up a few minutes later,he bummed a ride from a friend , and asks "can I take it and bring it back later--I have to go bring my wife to work--maybe I can do like you did with a hair dryer and get it started"?..
My friend said "Take it if you dare,but if it needs to be towed in again you'll be wasting a lot of money..and don't forget you owe me for diagnosing it".

So he takes off in the truck,and for the next 10 days he used a hair dryer on the computer if it refused to start!--in the meantime my friend found a used computer at a salvage yard while looking for parts for another car,so he bought it ($25 !) and called the customer and said "I think I found a good computer"..he put it in and the truck never acted up again..

Oh yeah..the truck had been taken to several other "good garages" in town and all of them charged the guy a fortune,then said "I guess we cant fix it--sorry"..

 

[aceroth]

I had a very similar problem with my old 92 explorer. The problem wouldn't appear til it had been driving for 2 hours or so. I replace the coil (I think Ford calls it a power pack on that vintage) cleaned the MAF sensor and replaced the ECM and a couple of sensors. Also took it to two dealers and two indepemdent mechanics. Never got it fixed but kept driving it til the tranny went. MFer stranded me half a dozen times. (I was in my early 20s and broke and stupid).
After I got rid of it, I was BSing with the best mechanic I know. He was sure I needed to replace the MAF sensor. He had a theory about what was going on that I dont remember and didnt totally understand. Might be worth a shot especially if you have a spare.

 

[dyeager535]

Its not related to heat unfortunately. Started it tonight, idled for about 30 seconds, started to try and stall for a bit, cleared up, then started trying to stall again, finally died.

Immediately broke out the multimeter to test the coil, but ran out of daylight before I figured out the truck and car remote coils (even though both look identical in the pics) are wired differently, so don't test the same way.

This time paid more attention to what it was doing, as I was in the driveway and in no hurry. Definitely doesn't seem to be specific to the coil.

Once it stalled, just sitting there dead with the key still in "run" the ECM commanded the cooling fan to turn on, which is indicative of the system going into limp mode. Odd of course, since it had already stalled and often/normally the fan comes on as soon as the check engine light is triggered. Also noticed that ONLY the check engine light was flickering. No other circuits seemed to be experiencing the same issue...gauge lights, dome lights, actual gauges were all solid/steady. Check engine light flicker was not a consistent/pattern but random, like a candle. Bright, dim, off, any variation of that, but rapid and seemingly random. Definitely not like when you are reading a code. I have spares of everything, and it was already loose, so I swapped out the ECM just to check, but that wasn't it. Jiggling what wires are accessible underhood didn't seem to make a difference in the check engine light flicker.

Pulling the PROM and putting it back in to get the check engine reset, was able to fire it right up, and idled fine for ~10 minutes, like nothing was amiss.

 

[Blazooki]

could it be sediment or rust in fuel tank? runs fine after it sits and the sediment settles cause theres no longer any fuel pressure...runs like crap once the sediment blocks the filter or the fuel pick up..runs like crap when the tank is low, put gas in it and it runs better. A bunch of chunky debris rolling around in the tank would act like that.

 

[dyeager535]

I'm going with no, unfortunately. New tank with the EFI swap, then had it down a couple (few??) years back to swap the pump/in tank hose, inside of the tank looked brand new still.

I will check the fuel pump relay. I was pretty confident I fixed the wires at the plug (the jacket had retreated from the crimps and the bare wire was starting to be visible on the harness I used) I suppose a short of some sort there could cause issues, since the ECM does have a reference wire for fuel pump voltage somewhere.

I can't get over the flickering light though. Whatever happens is somehow related to that light...if the light is off, truck runs as it should. If the problem is in the ECM wiring or ECM/PROM, one would think it wouldn't change if all I do is turn the key to off, pull PROM, reseat, turn key to run. No real movement of the wiring except at the ECM plug when monkeying with the PROM. Guess I'll have to jiggle that wiring if I can get the CEL to flicker again.

 

[diesel4me]

Some GM vehicles have the CEL powered by the same fuse as the cigarette lighter--it was common for some less than honest inspection garages to pop the fuse by sticking something in the lighter socket,then the emission tester couldn't get powered up (it plugged into the lighter socket) and I think it set off the CEL light...then the customer would get roped into having the problem repaired on top of the inspection fee..

Might want to see if your truck is set up that way--any short in the lighter circuit might be causing the problem..

Also GM cars & trucks had a lot of issues with poor grounds for the ECM and other wiring--more than one GM car I've seen that had fuel pumps go sour quickly and die shortly after installation were found to have all the ground wires under the passenger side kick panel all gangrene where they were screwed to the body..

 

[dyeager535]

I'm at least heartened that it gave me continuing problems and pretty quickly. Hopefully it gets worse so its 100% repeatable.

I'm usually real good about making sure all connections are good, to include dielectric grease, and nothing on this truck hasn't been disassembled/assembled by me by hand the last 20 years, but I have swapped a lot of things, so pinched or pulled wires are certainly possible, as are loosened bolts or nuts. The EFI grounds at the back of the head are suspect since I cant access them easy.

I wired the EFI up to an accessory fuse panel that is easily accessible, and I couldnt find anything wrong with that with some quick shaking and a look, but I can investigate the connections better. Plus the mini fuses are suspect, I noticed new Chinese fuses dont necessarily pop as they are supposed to.