Rough Rider said:
I have 99 Jeep Cherokee that when it gets warm the engine dies out. Sometimes it starts after it dies sometimes it doesn't. I've the fuel pressure checked when cold and the pressure was good. I've had a mechanic check it five times and can't find anything wrong with it (It always seems to run fine by the time I get it there the next day). Have any of yall had something similar to this?
Thanks
Your typical heat engine (gasoline, Diesel, whatever) is just a large air pump driven by fire. Focus on that last word - fire. What makes a fire? Heat, fuel, oxygen.
Stalling is usually related to losing one of those three. Since it will start and run, we can presume it's getting air - focus your effort on heat and fuel.
"Fuel" is obvious - gasoline. A failure in gasoline delivery will cause the engine to stall. Since electronic components don't like heat, let's see what electronics we have in the fuel system. Hm - fuel pump - which is too far from the engine to be affected by engine heat (and it's submerged in a cooling liquid anyhow - the fuel itself); and six fuel injectors (which are solenoid valves, and can be affected by engine heat.) However, losing all six due to heat would be rare - so let's leave this idea aside for the moment. Losing one injector - or even two - can make the engine run rough and lose power, but it shouldn't stall it. That leaves the control module for the fuel injectors - the ECU/SBEC/SMEC/whatever Chrysler calls it. Fuel injectors are driven by high-current transistors, and they have been known to blow out on occasion. So, hold that thought.
"Heat", in this case means, "spark." Ignition. The ignition system on late-model vehicles is a batch of solid-state components and a coil - and neither of those components enjoys heat. The solid-state components are in the ECU/SBEC/SMEC/PCM/whatever, so we'll test all of them at once. The coil is bolted to the side of the engine - while it's on the side away from the exhaust, it's still bolted right to the engine, and can be affected by engine heat.
How to individually test for heat-related failures? Easy - you heat-soak individual components. Here's how:
1) Before you do anything test-wise, how long does your engine usually run before it stalls out? two to five minutes? Double that - we're going to assume "five minutes," so that gives us ten.
2) With the hood open and a largish fan blowing through the engine bay (deflecting off of the open hood will serve,) idle your engine for ten minutes. Idling is a great way to heat-soak engine parts, but we're not trying to do that. We want to make sure it
is heat related, so we're trying to do a "negative results test" - a test which is supposed to allow components to pass. If the engine will idle for double the usual failure interval without stalling, while getting auxiliary cooling air, we'll go with the heat failure idea.
3) Once you've passed this test, go have lunch. Leave the fan going (if you can) - you want everything to get back down to ambient temperature. A sandwich and a couple of beers should do.
4) On your way back out, grab your S/O's hair dryer. You should probably keep one in your toolbox for tests like this...
5) Locate the ignition coil (should be on the rear half of the engine, passenger side) and the ECU/PCM/SBEC/SMEC/whatever (should be a plastic box on a fender liner or firewall, probably on the passenger side. There will be a large plug with lots of wires going into it.) Get enough extension cord to plug in the hair dryer and have it reach the engine bay.
6) Start the engine and let it idle. Turn the hair dryer on HIGH and point it at the ignition coil. If it's a heat-related component failure, and it's the ignition coil (I'm thinking it fairly likely, I've seen this sort of thing before) you should stall out your engine rather quickly. If you make it a full "ten minutes" (or whatever double your failure interval comes out to be,) turn the engine off and let it all cool down again.
7) Repeat with the ECU.
If it passes both of those "accelerated heat soak" tests, report back and we'll see what else we can come up with.
Yes, there are a number of odd things in my tool box - but they're there for a reason. Polaroid? Especially necessary when working on automatic transmission valve bodies! Also useful for any semi-complex assembly.
Hair dryer? Now you know why
that's there.
White gloss nail polish? Works for bring out timing marks and witness marks. Replace this bottle about every other year (there's only so much shaking you can do.) White or clear also works as "threadlocker" on small adjustment screws - I also use clear "pearl finish" or "matte" on small screws as a threadlocker - like scope mounts on firearms.
Toothbrushes? By the time I throw them away, there aren't any bristles left. The Nylon bristles work well in most solvents, and the handles are usually Nylon as well. Nylon is cured in sulphuric acid...
Surgical instruments? Dental instruments? I buy these at surplus outlets, and get lots of use out of them - from the four-inch locking forcep to the 20" long hemostat (useful for pulling wiring through the firewall.)
There is very little that has
only one use.
