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Engine Stall - Seeking Potential Diagnosis

5K views 49 replies 14 participants last post by  Jeff's SS 
#1 ·
I finally got the impala back on the road. Still fine tuning and getting everything back to working order. Something happened yesterday, and I am striking out on what the potential cause could be.

I was driving on the interstate at 5:30pm (traffic), so it was stop and go. Car was driving normal. I was driving forward at idle; I applied the brakes; and after I came to a complete stop, the rpm's dropped sharply, the car died and would not restart.

I pushed the car to the side of the road, and checked everything. All fluids were/are good, coolant temperature was good (150-160 degrees), gas was getting to the engine (checked schrader valve port with car on/engine off), intake was clear and clean, all sensors were plugged in, no check engine light, grounds looked solid, spark plug wires were checked at plugs and opti, no fluid leaks anywhere, and the battery/starter were strong and tried to turn the engine over. I let the car sit for 10 minutes and tried to restart...nothing. The starter would engage, but the engine would not turn over.

I called a tow truck, and while I was waiting I continued to check things and tried to restart, but no success. After the car was dropped off in the driveway, I tried one more time to turn it over, and the SOB started up like nothing was wrong. I didn't change or check anything. I let it idle for 10 minutes with an occasional rev. No issues. Turned it off and restarted with no issues.

At this point, I don't know where to start looking for potential problems, and I am looking to see if anyone here can help diagnose/troubleshoot my car issue(s). Anyone with a similar circumstance?

Car mods: 357 ci by Golen Engines, LT1 aluminum heads with larger valves and bowl porting, Cam Duration 224,230 Lift .574,.569, 1.6 RR, rebuilt/upgraded 4L60E, 2800 stall converter by Edge, 30 lb/hr flow matched injectors Bosch, CAI by Clear Image, F-body MAF, try-y headers and cat back exhaust by Clear Image, electric water pump, 160 thermostat, deleted Cats, EGR and Air Pump, and PCMforless tune for all of the above. Everything else is stock. No forced induction.

I should note that I was having idle problems caused by a faulty TPS. I replaced the TPS and reset it to read 0.70 volts (0.68 ideal). After I replaced the TPS, I also reset the IAC. The engine appeared to idle perfect after these corrections were made. I even made another 30 mile trip with a lot of stop and go prior to this stall incident, and I had no issues.

Thanks in advance.
 
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#4 ·
check your fuel pressure with a gauge, classic fuel pump symptoms.
you can press open the schrader valve on a empty gas tank and you'll get gas out.
 
#5 ·
X2 seen it/experienced it multiple times. Most likely a burned connection on the in-tank wiring harness. They work when things are cool, but when stuff starts to heat up the connections drop out and it shuts down. When things cool off or get jostled around (IE loading on tow truck) and it goes back to working. Check fuel pressure with a gauge (should be at least 40ish with key on engine off). If it dies on you again, you can sometimes get them going by rapidly banging on the bottom of the gas tank in the center. I've gotten a few going this way. At least good enough to get home...
 
#6 ·
Ok, thanks guys. I will start there and report back my fuel pressure.

I replaced the fuel pump with an Airtex about a month ago. When I did this, I also cleaned the electrical connections, but I ended up reusing the spade connectors. If I have solid fuel pressure, then I might drop the tank and solder all the connections to remove that as a potential failure. I may even replace the sending unit with a new ACDelco since the new unit appears to have fixed a lot of the known issues with the original.

Thanks again.
 
#8 ·
You may want to consider a different fuel pump anyway. I haven't been all that impressed with Airtex pumps. They seem to be a lot louder than the Delcos. I had a dead one right out of the box too. I wouldn't have even bought it, but I knew I'd be scrapping the car in less than a year. Check Rock Auto on the Delco pumps, they were $80-90 the last time I bought one. Not much more than the airtex.
 
#13 ·
Tested the fuel pump.

Ignition on/Engine off: 42 psi (dropped about 5 psi over a couple minutes)
Engine on: 42 psi (idle), 38 psi (up to 3,000 rpm)

No trouble starting, idling or reving. Sounded great.

The readings sound a little low, but not low enough to be the direct culprit for causing the car to stall and not restart. Something like the wiring could be at fault. I at least agree that taking a look at the wiring harness and terminals on the sending unit/pump to see if there could be a potential corrosion or varnishing issue.

Like I said, the fuel pump is new, and I cleaned all the terminals prior to reinstalling. The spade connectors are not the most reliable.

Between the heat and vibration, does anyone think the pump or wiring is still a potential cause?
 
#14 ·
Those numbers sound pretty normal, but you may have to wait until it fails again to diagnose it. Check the pressure when it stalls next time.

Also, have you tried the wiggle test while it's running (wiggling all the various wires under the hood)? I found a break in an ICM wiring once this way that was causing intermittent stall problems.
 
#16 ·
When I was on the side of the road, I did the "wiggle test" on the connectors and grounds to make sure all terminals were snug and I didn't have any loose grounds.

Grounds I checked: LH & RH frame grounds at front of car, grounds next to ICM, LH rear block ground, RH front of block where negative battery cable connects, negative battery cable fender ground, and the additional frame ground that comes on my Innovative Wiring battery cables.

When I re-installed everything on the car, I wire brushed every ground terminal and coated with dielectric grease before torquing down.

I painted the frame and engine compartment. Before installing the harness and grounds, I scuffed all ground surfaces up, but I might go back over these and make sure I have exposed bare metal where I painted.
 
#17 ·
your problem most likely is an electrical short some where. since the wiring was messed with check that all the wiring has LOOM covering the small wires. remove the PCM check all the wiring connectors for damage chaffing on the metal frame/inner fenders..

could be the fuel pump did shut down , then after the tow job vibs it started to work again but some wire shorting can do the same thing.

I would keep the fuel gauge and a volt meter on you at all times so when it fails again your ready ....

with no codes again some wiring problem..
 
#18 ·
J cat - Will do.

Alternate idea: Could it be the ECU itself trying to learn how to control the car. I literally took the entire car a part and put it back together. The car was almost completely stock prior to this project. Now it is extensively modified. Nothing over the top, but it is not stock.

I finally got the car running about 3 weeks ago. I took the car on a handful of short (< 3 mile) trips and just two longer trips, so there really hasn't been much time for the computer to learn all the new changes that I forced on it.

I will check the wiring, but does anyone think the situation I described above is plausible.

Thanks.
 
#23 ·
on my 96 and other GM vehicles I never had the PCM re-learning due to battery power removal cause a stall then no re-start..

like I said you have an electrical intermittent so you must have your test tools available to find out whats screwed up.

if this was a sensor you should get failure code which would be good to narrow down this issue.

some have had bad wires at the PCM along with the connectors etc..

the fuel pressures dropping from in tank connector are usually after its be running awhile and the bad connection heats up creating a greater resistance ..

measure to voltage at the rear license plate fuel pump connector with the engine running see what voltage is there should be about one volt below the battery volts approx...
 
#19 ·
By checking spark, you pulled a plug wire off and observed spark while cranking?

If that is the case, you have a fuel pump electrical issue. Open the trunk, on the left side is the fuel pump ground on the trunk hinge support. Clean, seal and retighten this connection. Then drop the fuel tank and fix the wirng harness bulkhead connector. thats were your issue is. I personally would install an upgraded fuel pump harness from racetronix or one of Garys hot wire kits.

Chris
 
#20 ·
Rocko, yesterday when I checked the pressure, I also confirmed spark in plugs 1 and 4 as you described.

I contacted Gary. He said that he has made one, but does not currently offer a fuel pump harness. He did suggest the same root problem with the fuel pump ground on the trunk hinge. I checked and it was tight an corrosion free. I will add this to the list of things to clean. I will also expose bare metal, replace the self tapping screw with a standard nut/bolt, and apply dieletric grease. I will also check for a short in the line.
 
#21 ·
just a thought but i had a similar problem a few years back. drivin down the road and car would die after a few min. sit and let it cool and she'd restart and run fine. found out that the motor was overheatin the ignition coil and breakin it down. put a new one on and it was fine. might wanna try that if you have an extra one or the easy way, let it run til hot and dies, use a blow gun to cool the coil then try to restart.
 
#22 ·
I did reuse the original ICM and Coil, but I cleaned everything up and put new thermal paste between the ICM and Coil before reinstalling.

I don't have a spare. A new ACDelco isn't cheap. Amazon has a good price, but not cheap. I may pick one up and the next time it stalls out I will check the fuel pump to see if it is working properly. If the fuel pump is okay, I think the ICM is a likely culprit.

Are there any proven aftermarket ICM's or should I just stick with the Delco?
 
#24 ·
Thermal paste is a good move. PC CPU to heat sink paste best.

This issue strikes me as more of an ignition/coil/ICM related issue, but we're all just shooting at internet wind here, so who knows? In addition to testing/checking/replacing these components, an additional measure you can take is to get the heat sink/ICM off of the block by placing washers behind them thus creating a stand off that allows air to circulate directly behind the heat sink and decreases the amount of conductive surface between the ignition components and block. Like so:

 
#25 ·
Those spacers are a good idea.

I used arctic silver thermal paste which is more commonly used in CPU/PC applications.

I will post back on the following:

- Voltage at fuel pump using connector near license plate
- Re-ground pump in trunk.
- Check wiring at Coil and place washers to offset from head.

I will probably wait for the weekend to drop the tank and look at the harness.

Tonight or tomorrow, I will probably take the car in a loop around the house to see if I can't recreate the stall circumstance. I will have the pressure gauge and multi-meter on hand.

Thanks guys, hope I/we can figure this out. I just hate not knowing the exact problem.
 
#34 ·
Those spacers are a good idea.
Maybe...Maybe not. Just throwing this out there as you have already spaced the Module off the head. I believe this was a popular topic on the Z28 Forums which also run a similar engine with Aluminum Heads and was discussed before. By spacing it, you have just reduced the HeatSync effect on the ICM.

Some felt that raising the ICM off the head for additional air gap allowing it to remain cooler is somewhat bogus. The best way to explain this is to think of a Computer chip/Processor that uses a large heat sync. The idea behind the heat sync, is the thermal Paste helps to conduct the heat from the componet into the Heatsync. The faster more powerful chips use larger heatsyncs to draw the heat away from the componet and into the into the heatsync, they dont use a Air gap.

Now, apply the same idea to your ICM, the cylninder head acts as the heatsync. Raise the ICM off the head to give it an air gap and you have now lessened the HeatSync effect of the cylinder head. So to me, adding a little airgap, does nothing more than reduce the heatsync effect that the cylinder head was providing. We are talking theories here though....but not quite. I needed to see some numbers myself to confirm this.

There is a thread here somewhere from a while back where this exact discussion was brought up. Some believed in the airgap and some did not. Again, the therory that removing the device from a hot engine would keep it cooler. So they ran some tests and what they found was interesting. IIRC - they found that there really was minimal change in temps for the ICM whether it was on the head or raised while the engine was running. However, they did find that after the engine was shutdown, the ICM that was raised took longer to cool down than the one that was bolted right to the head.

So what does all this blather mean....I dunno know. :) But IMHO, if the temp changes are nill while the engine is running, then all raising the ICM does it keep it exposed to heat longer after it is shutdown. Heat is what can damage electronic componets or they wouldn't have put a HS on it. To each is own and unless I can see more numbers I will continue to keep it applied as the factory engineers intended using a good Conductive paste. Many of these cars on the road without this mod and my ICM has been clicking away for many years/miles. But since I just jinxed it with that comment, its good I have a spare. :p

Good luck and hopefully you can track down your intermittent issue.
 
#26 ·
Alright, it's summer in Florida, so that means rain every afternoon.

I was able to accomplish some stuff.

I regrounded all my connections to remove this as a potential cause. Each body/frame/trunk hinge point and ground wire termination was wire wheeled to bare/clean metal. I then coated all surfaces with dielectric and torqued everything down.

I also installed some washers between the Ignition Coil/ICM assembly and head to provide some air space and hopefully improve cooling. I also cleaned up the grounds at this location too.

It then started to rain, so I wasn't able to perform the voltage check on the fuel pump at the rear connection.

I will get to that stuff and try to recreate the stall with tools in hand.
 
#27 ·
ICM heat fail!

I had the same prob on my 96. turned out to be the ICM failing from heat soak. Cold start Ok, then failed when hot like you turned the key off. I had the beast towed home twice only to have it start up after cooling down. Replaced the ICM and put a heat wrap material spacer between the ICM and the head. No probs since. Oh and I didn't use an AC Delco ICM, just an after market one. We'll see how it goes. Plus I keep a spare in the console....
 
#28 ·
Engine Stall

Many have mistakenly coated the back of the ICM with dielectric grease instead of thermal grease,but there is something better. It's called "Artic-Silver 5",and it's used for heat-sinks by computer geeks. Available at RadioShack,and sometimes Wal-Mart has it too. Little pricey,but you don't need much anyway.
 
#29 ·
Slow - That is exactly the product I used. between the ICM and heat sink surfaces. I had some lying around from when I modified and repaired xboxes.

Iggy - You and Shilaeli Hugger seem to have similar symptoms to what I am having. Could you describe yours a little more..."then failed when hot like you turned the key off"?

How did it stall (abrubtly, stutter, hesitation, etc.)? Then when you were trying to restart, how did the car behave? Did your computer throw a code when this happened?

Still leaning towards intermittant wire failure with fuel pump, but your circumstances are notably similar to mine.

Bottom line, you need three things to start an engine: air, fuel and spark. I know it's getting air, but I see the potential for both the fuel and spark.

Heat/resistance could be building up in the fuel pump wiring.

Engine heat could be causing the ICM to fail.

Once cool, both the wiring and/or ICM could return to normal operating condition.
 
#37 ·
When mine quit, I was driving at road speed 45-55, and engine just shut off, no sputter or hesitation. would not start but had Fuel press. New ICM and a piece of aluminized heat wrap material, the prob. went away...
 
#30 ·
Engine Stall

Damaged,or worn connectors/wiring can behave the same way sometimes. Wires can be broken inside their insulation,and not be visibly damaged.
 
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