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740 Ignition power stage overheat failure

spencerstaats

spencerstaats

New member
Joined
Aug 7, 2018
Location
New York City
Made the mistake of driving my car in upper-80s weather last weekend with Best Buy's insignia brand thermal compound on it (though this was at highway speeds, 50-60mph, worked fine ~30min earlier in traffic with similar ambient temp), and I'm pretty sure I've cooked my power stage. I'm getting near identical behavior to symptoms described in Brickboard 7/9 FAQ, though mine is definitely permanently damaged as the car not only stopped running/no restart when hot, but when it does start after cooling off the ignitor is only sending spark every other time at best and barely idles (and of course the LH2.2 idle valve tries to play catch-up very poorly).
After all this, (and having had this in my car since February with no issues, and the car has a tropical fan clutch), I looked at the specs for the Insignia stuff and sure enough the max "storage" temp is 200 degrees fahrenheit - does anyone have experience with different thermal compounds for the power stage/heatsink interface, or know what temp range the ignitor will run/spontaneously combust at?
I saw in the Brickboard FAQ that (now defunct) Radioshack thermal grease was mentioned, looked at the SDS, and it seems to be Super Lube's silicone thermal grease with an operating range of -40 to 500+F - probably gonna order some of that now since it'll work even if the power stage immolates, but definitely interested in others' experiences with this because I didn't find threads about this when searching.
 
kyote said:
I doubt very, very seriously that inferior heat sink compound killed your powerstage, and LOL at upper 80's temps from South TX :)

Found this during my googles also, may help
http://www.stepbystepvolvo.com/Resources/Volvo No-Start.pdf
Click to expand...

I agree! Cause these temps (and not running AC either) are far from the underhood temps these parts were designed for; do you guys know if the Bosch (now made in Taiwan) power stages are crap now? I'd put one from FCP Euro in this February and it ran without issue til now, then steadily deteriorated over a period of about 5-10 highway miles.

Part the car had in it from FCP was Bosch 0227100124, and the part that's been on my car since before I bought it was an identical part number but made in Germany and with "080" in the bottom right corner.

The car starts and barely idles, but isn't a no-start and there is tach signal so I know my hall sensor is working (already checked connector and it's tight and clean).

Could any of this be brought on by a failing alternator? Mine (original 80A ext fan Bosch) has been in the throes of diode failure throughout the weekend but on Sunday there was miraculously no longer any visible voltage ripple in any of the incandescent lighting - voltage regulator was also going though as it was providing around 15v at idle :-(
 
I use silocone heat sink compound for stuff like voltage regulators that are bolted to a heat sink. That can be found at a good electronics supplier. Like Digikey for example. Don't know any ratings.

What I would suspect is the ignition amp is just bad.
 
kyote said:
I doubt very, very seriously that inferior heat sink compound killed your powerstage, and LOL at upper 80's temps from South TX :)

Found this during my googles also, may help
http://www.stepbystepvolvo.com/Resources/Volvo No-Start.pdf
Click to expand...

Just finished reading that guide, and I'm definitely gonna use it to guide my multimeter probing later this week or whenever I can get out without rain when I'm not busy otherwise.
Definitely learning from this that all original parts that work should just stay, because the original one also had only dried up thermal compound half-covering the contact area when I pulled it, but worked perfectly fine last summer and never showed any issues in warmer temps.

Should've said this in the first post, but I replaced with the new part earlier this year because I've been chasing an even miss across all 4 cyls, with new cap/rotor, good plug wires and coil, good hall sensor, and seemingly good injectors to no avail.
 
dl242gt said:
I use silocone heat sink compound for stuff like voltage regulators that are bolted to a heat sink. That can be found at a good electronics supplier. Like Digikey for example. Don't know any ratings.

What I would suspect is the ignition amp is just bad.
Click to expand...

I agree here, and I'm probably gonna get some of the superlube thermal grease locally - I'm just worried if something other than heat caused it to fail cause I don't want to wreck my OEM part that's NLA
 
I'm running a good used 960 power stage on my 240 because wasted spark and I have it bolted to a small piece of angle alumuimum and used whatever junk thermal goo I had around and it seems to hold up. gets pretty hot though. Maybe 60C?
 
esmth said:
I'm running a good used 960 power stage on my 240 because wasted spark and I have it bolted to a small piece of angle alumuimum and used whatever junk thermal goo I had around and it seems to hold up. gets pretty hot though. Maybe 60C?
Click to expand...

Ah! That still sounds pretty decent though, but makes sense the crap I put on probably didn't survive a warm day in that case due to it being close to the temp ceiling for the compound.
I wish I had all the bits to go wasted spark right now and ditch the dist etc.
Are you using the Huco power 960 power stage from CFloMoto? I'm thinking the H?co power stages could be more reliable than the Bosch now since that's what they sell.
 
spencerstaats said:
Ah! That still sounds pretty decent though, but makes sense the crap I put on probably didn't survive a warm day in that case due to it being close to the temp ceiling for the compound.
I wish I had all the bits to go wasted spark right now and ditch the dist etc.
Are you using the Huco power 960 power stage from CFloMoto? I'm thinking the H?co power stages could be more reliable than the Bosch now since that's what they sell.
Click to expand...

I am running a stock used bosch 960 power stage I got from here. PN 0 227 100 203
 
esmth said:
I am running a stock used bosch 960 power stage I got from here. PN 0 227 100 203
Click to expand...

Ah, thanks for the info! is the center grayish-white plastic with raised lettering? the Bosch parts being sold now are all black with white lettering being printed on them - my old one was white plastic on the raised bit with raised lettering.
 
spencerstaats said:
Could any of this be brought on by a failing alternator? Mine (original 80A ext fan Bosch) has been in the throes of diode failure throughout the weekend but on Sunday there was miraculously no longer any visible voltage ripple in any of the incandescent lighting - voltage regulator was also going though as it was providing around 15v at idle :-(
Click to expand...
A failing alternator might be able to generate enough electrical noise to cause false triggers from the LH2.2 distributor pickup, but it's doubtful. I'd re-check the disti pickup wiring, and the EZK connector.

It's very unlikely that under-spec'd thermal compound would cause a short term failure. Maybe if it all seeped out and hardened over months or years. You could certainly try swapping the ignition module (besides, a spare in the trunk is good insurance).
 
bobxyz said:
A failing alternator might be able to generate enough electrical noise to cause false triggers from the LH2.2 distributor pickup, but it's doubtful. I'd re-check the disti pickup wiring, and the EZK connector.

It's very unlikely that under-spec'd thermal compound would cause a short term failure. Maybe if it all seeped out and hardened over months or years. You could certainly try swapping the ignition module (besides, a spare in the trunk is good insurance).
Click to expand...

Will do - definitely a lot of unknowns, but I'm hoping my 100A Denso from Phil will clear things up a bit too cause the Bosch was getting real real bad in terms of ripple though it never caused running issues this weekend prior to the power stage giving out.

Had to start and move the car for some utility work yesterday, and it idles fine now but will randomly cut out when going above idle every couple hundred revs or so, which leads me to believe that this is definitely the power stage since cold idle is unaffected (and tach remains true to engine revs, never drops straight to zero). Definitely took more cranks to start now though.

Gonna have to wait til next week to put the old power stage back cause I don't want to put it in with the old thermal compound and I'm waiting on the new stuff; but I'll update this thread with my findings once I start to poke around with the multimeter and piece things back together.
 
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