automotive thermal paste????

[XWrench3]

i own a 2000 GMC Jimmy. it has developed an intermittent misfire. there is some sort of module mounted on the same bracket as the ignition coil. it is mounted onto an aluminum heat sink, and knowing what i do (not all that much) about computers, i thought that it may have some sort of thermal paste to aid in heat transfer, that may have dried up over the years and miles. well, i took it off last night, and sure enough, it does. and the stuff is falling off in flakes. i have no clue if this is what is causing the misfire or not. but it seems obvious to me that if an electrical part is getting hot, it is doomed to failure much sooner than it should. of course, i do not have a drop of thermal paste here. (i would need 4 drops anyway due to the shape of the part, and the way it is mounted) do they use thermal paste in automotive settings? and if the auto parts store has none, what should i use until i can order a tube of it online? the nearest computer store is over 40 miles away. i have a silicone grease with some sort of gold colored flake ( i am assuming its copper) that is meant for use on brake pads, and i have aluminum rich anti seize grease. but i have no clue if or how effective either would be at transferring heat. in the motorcycle industry, the only thing we ever used was dielectric grease to aid in cooling electrical parts. which was mostly voltage regulators, or the occasional diode pack. cdi boxes are filled with some sort of silicone rubber type adhesive.

 

[C0RR0SIVE]

If you have a misfire the ICM or coils are already toast, and to be honest, that thermal paste will dry up after about an hour of a baking hot engine cooking it. You can buy thermal paste for automotive applications at autozone for like $2 a packet.

 

[XWrench3]

so is the automotive thermal paste made to withstand the heat? or will it dry up just as fast? there was silver colored remnants left on both the module and the heat sink. but that is 15 years old, and 140,000 miles on it as well. i can not imagine any kind of grease / paste / etc. would stay in a semi-liquid state for that long. if the check engine light is not being tripped, is there a way to find out what the cause is w/o paying a GM dealer $120.00 to hook up their scanner for 2 minutes?

 

[Dauntae]

Last time I dealt with a misfire was on a I think 89 S-10 blazer WITH A 4.3 a friend owned, We used to go wheeling in it and it wasn't kept so great on shape, Turned out his wires were arching, Seen it in a dark garage, every time he revved it it kind of backfired, where the wires crossed over each other you could literally see spark jumping from one wire to the next, Not saying that is your issue because that Blazer was in sad sad shape and a beater but it could be any number of things causing that to happen, Need to go through one thing at a time and check. Process of elimination so start with the simple things first, Get the heat sink fixed and eliminate that off the list. Also unless the engine light is tripped the scanner won't pull up any codes, AND if it did trip you can either use the flash code by tripping 2 pins with a paper clip or just go to autozone and they check them for free for you.

 

[XWrench3]

i did check for "spark leaks" (DARK overcast night w/ no moon) as the entire ignition circuit is 2 or 3 years old. no visible leaks like there was last time they got replaced. its acting different than last time also. i used plain dielectric grease to get it back into service, as the closest Auto Zone is 45 miles away (almost everything is), and i am not going to walk! lol. i drove it up the road and back about a mile, mostly to check for oil leaks on a fresh L.O.F. i will get a chance later today to see if that made any difference. i pulled the cap and rotor, and other than the terminals being a bit crusty, they looked fine. i cleaned them up and reinstalled them. i hate problems like this, as they usually end up leaving me stranded. i actually miss the days of points and condensors. they were easy and cheap to fix, and i could do it along side the road if i had to. tow truck NOT required.

 

[C0RR0SIVE]

The grease tolerates it, but it dries out, it's meant more for the large imperfections between mating surfaces, similar to how thermal paste in a PC is used for microscopic cracks, on a car, that paste has to fill much larger potential cracks. BTW, it's meant to dry out after so long, as long as it's filling that gap, it's doing it's job on a car.

But I am a bit confused, you have a cap and rotor style ignition, but an ICM? Kinda throws me off a bit, usually don't have both like that in my limited experience.

That aside, doing the visual arc test is pointless, I suggest replacing plugs, and wires to start out, if that doesn't solve the issue, have the ignition coils checked, you can usually use a multi-meter to test those, but you need to know your values. Some autozones will also test the coil. If bad replace and see what goes on.

Next course of action, replace the rotor and cap...

If I am not mistaken, your Jimmy should be using Double Platinum or Iridium spark plugs, I highly suggest using AC Delco branded plugs as well, nothing beats OEM plugs for a stock engine, even if the plug is $10 a pop. If your plugs, or rotor is worn, it could be causing an increased strain on your coil, and can cause the coil to die an early death, or even potentially the ICM.

AND if it did trip you can either use the flash code by tripping 2 pins with a paper clip

Pretty sure that doesn't work on the 2000 Jimmy, uses the same basic computer and electrical system that our GMC Sonoma uses (Book covers both vehicles) and for all the other cars where you can get the CEL/MIL to flash out codes, it will list the two digit code, but this book states that you must use an OBDII scanner.

Would be nice if the CEL was illuminated though, would give us a path to start on.

 

[XWrench3]

yep, cap and rotor, plus the icm and coil. personally i like the individual ignition coil for each cylinder. it does have double platinum plugs in it. they have roughly 40,000 miles on them. they are a PITA to change, and i did not want to do it any sooner than i had to. cap, rotor and wires are newer than that. the plugs are AC Delco also. cap and rotor are as well. but the wires are Autolite, because they have a lifetime warranty. so buy them once, and they pay for the next set. or two, or three. well, i guess i am going to find out how it works. i need to make a quick grocery run.

 

[XWrench3]

well, it seemed a bit "zippier", but the oil temp did not get to full operating temperature. so i will reserve judgement until the truck gets all the way warm. i guess i am going to have to make a special trip just to try it out. i do not want to be fiddling around with this thing when it is -5 f with a 20 mph wind!

 

[C0RR0SIVE]

It does this mostly when it's warmed up? That's almost a sure fire sign that it's an ignition coil or ICM.

If you have a multimeter, you can test the coil, as well as other things, you have a 2000 Jimmy with a 4.3 v6 and an EDI ignition correct?
1: Check the resistance of sparkplug wires, they should all be at 30K Ohms or less
2: Pull the spark plugs that are easy to check and verify they are in good condition.
3: Perform the following to check your ignition coil
a: Detach the primary electrical connector from the coil
b: check to make sure the coil is receiving battery voltage with the ignition key on, engine not running (you should have the exact same voltage that's present at the batt)
c:Using the multimeter to check for ohms, connect one probe to the coil body, and the other probe to the primary terminal on the ignition coil, you should see infinite resistance.
d: now hook the meter to both of the primary terminals and check for resistance, you should see 0.2 to 0.5 ohms
e: Now, attach one probe to a primary terminal, and one probe to a secondary terminal - you should not see infinite resistance, but should see between 5,000 and 25,000 ohms.
Primary = where the wiring connects
Secondary = where the spark plug wire connects

Next, are you sure when you put the distributor cap and rotor on that you had it in time?

It's sort of dangerous to do this, but if the misfire is rather constant at idle, take a pair of sparkplug wire pullers with some rubber gloves on, and pull the boot on each spark plug, engine tone should change, if it does, move to the next plug. If you find one that doesn't change the engine tone much, you have found the faulty cylinder. No engine damage will occur, but the engine computer might get a tid-bit upset and throw a check engine light for sure at this point.


Please, if you already have a check engine light on, say so now, and go to Autozone, or any autoparts stores, and ask them to pull the codes, and tell us the exact codes you have, they will be like P0300, or similar.

 

[XWrench3]

WOW! do you work @ a dealership? i can not find specs like that. i have tried. yes, it is a 2000 GMC Jimmy w/ a 4.3 Vortec. as far as the "EDI" ignition, i am not sure. it has the ignition coil and module mounted to a bracket bolting to the intake manifold. unlike the old HEI, which carried the coil in the top part of the cap. it has to have a crankshaft trigger coil, because other than the rotor, there is nothing else inside of the distributor. i will test the coil, wires, and look at the 3 semi easy plugs. as far as timing, when i first got the truck, i put a new set of standard (cheap non platinum) plugs in it. that is when i realized what a pain they are to change. anyway, i did not know it had a crank fired ignition, and i tried to adjust the timing like every other car i have owned. i usually put an additional degree or two, to help fuel mileage. well, you can twist the distributor half a mile, and the timing stays the same. thankfully, i made a mark on the firewall and distributor prior to twisting it. so i just re aligned those marks, and tightened down the clamp. the intermittent miss is not regular, so i do not think its one cylinder. and it seldom misfires at idle. it does it most at highway speeds, at an even and steady speed between 40 - 75. i wouldn't know about anything over 75. i do not cruise that fast. speeding tickets cost to much money now days! as far as taking one wire off at a time while running, i think you would have to be a contortionist, AND have a special set of pliers for 4 of the 6 plugs. so that is out. there is no check engine light on. it does light up when i start the truck, and goes back out immediately. so i know it is working. but no error codes are being kicked out. which is fine by me. / my wife's car has a check engine light on, and i had it checked. its a fault code from the fuel TEMPERATURE sensor! i have no clue why anyone would measure the fuel temp. its not like they are going to heat/cool the fuel on its way to the rail. the fuel is almost always going to be within a couple of degrees of the ambient air temp. so why mess with it. its just one more unnecessary sensor to go bad and cost the owner money. GRRRR //// anyway, back to my heap. you have certainly given me a lot to work with. Thanks! i will let you know what i find.