So I keep frying PTU's.

[BrodieSkiddlz]

Last week, I bought a new power transistor unit online because mine had stopped working. (I tested the part as per the service manual and confirmed it had gone bad, only 3-6 worked) When I got the replacement, I tested that part out and it was working fine, so I installed it and gave it a shot. No go. I took it back out and checked it again, and the only transistor that worked was the one for 3-6.

So I went to the junkyard and by divine miracle I found another one. 60 bucks of course. Checked it before I bought it and it worked fine. But the same thing happened here too, except the only transistor that worked after cranking was the one for 2-5.

The only thing I can figure out is there must be a short somewhere, grounding out the signal or something and frying these things. My only theory on why I ended up with different transistors going out was maybe the when I stopped cranking it, the crankshaft was in a different position each time, leaving a different cylinder ready to fire for the next attempt. If that makes sense. I'm not sure how to explain it.

Anyone ever had a problem similar to this? I imagine its time to get the multimeter out and start testing everything but I really haven't a clue where to begin on this. Its a 94 SL cali-spec auto, and I've heard from Stealthee earlier in the week that its a little less likely to be the ecu. But I'm willing to check whatever I have to. Gotta get to work in this thing. By the way, I'm going to order a new OEM PTU from 3sx friday. I just want to make sure I won't fry it when I put it in.

Thanks in advance for the help. I'll check this again as soon as I can. My grandfather passed away yesterday so its bound to be a busy week, but I'll make it a point to come back soon.

-Robbie



Moved this to non-turbo thread. Accidentally posted in the turbo section first.

[stealthee]

Sorry I couldn't talk earlier Rob. My phone was literally below 5% when you called. Hopefully RealMcCoy or someone posts up and is able to guide you in the right direction.

[TUFFTR]

Swap ECU's dude.

[BrodieSkiddlz]

Well I had to be away from here longer than I wanted to be, but it was for a good cause I suppose.

And its okay Brian. It was just a spur of the moment thing anyway.

And I guess I will start looking for another ECU to try this with. I'll probably try to test mine if I can to confirm that's the problem first though.

[Jimvr4]

The ECU drives the PTU so if you're frying PTUs it is because you have a bad ECU. Do NOT try this again in ANY car unless you get this ECU fixed first.

[BrodieSkiddlz]

I removed my ECU this morning, and opened it up to check for leaky caps but I'm not seeing anything leaking, nor have I noticed the odor. However it seems that someone has definitely tampered with the harnesses before, which really has me upset. I was hoping to not find someone else's handy work down there.

So I'm guessing my next step is to check all the wires involved to make sure they're still sending a signal. I suppose this is what I'm supposed to follow? : http://www.stealth316.com/images/ecu94-1.gif

If I'm missing something, please fill me in. Thanks guys.

-Robbie.

[BrodieSkiddlz]

And before I mess something up, I just want to verify that I will be putting the positive lead from the multimeter to whatever number pin I'm checking for voltage, and the negative lead would go to the ground pin on the ECU? It says in the page from stealth316 the ground is pin 26. Is that right or am I reading it wrong?


Furthermore, If I need to check the pins for the PTU A B and C, it says checking conditions should be with the engine speed at 3,000 RPMs.... What if it won't start at all?

Gotta ask the dumb questions.


EDIT: It looks like pins 75-78 were tampered with (white wires). They have some fairly large gauge green wires spliced into them. Black wires are also spliced in. I'm not sure what the bigger wires or the smaller black wires are for, but the service manual says 75 and 76 are for the heated front o2 sensor, and 77 is the o2 sensor heater. I didn't see anything for 78. I'm guessing the previous owner spliced in an air fuel ratio gauge or something. I don't know if that has any correlation to my issue or not but I thought I'd mention it.

Come to think of it, I only looked for a moment, so the big green wires might actually be like a cover sheath for two of the o2 sensor wires to go into the engine compartment, simply there to keep the two together. But for all I know at this point it may be a wire. I'll have to check on that.


EDIT: Big green wires are simply sheaths carrying the o2 sensor wires to the engine compartment. I don't know why I didn't think of that first. Also found another white wire that was tampered with. Number 60 - heated rear o2 sensor. I'm still not clear on what the black wires spliced into the white wires are. They're coming from somewhere further down the harness. Under the console.

[Chris@Rvengeperformance]

The stock harness is squirrely like that, I wouldn't count on it being tampered with.

[DrGonzo]

EDIT: Big green wires are simply sheaths carrying the o2 sensor wires to the engine compartment. I don't know why I didn't think of that first. Also found another white wire that was tampered with. Number 60 - heated rear o2 sensor. I'm still not clear on what the black wires spliced into the white wires are. They're coming from somewhere further down the harness. Under the console.

The Stock O2's have the black wire as part of the wiring. I think it is used to ground the O2's to a common point to decrease ground noise. Both O2's should have that black wire.

[BrodieSkiddlz]

That's good to know DrGonzo. Its actually been fixed now. Turns out I had poor connection to the PTU from the coil pack and someplace under the motor. I have yet to look at it myself. I had a guy come take a look at it and he pretty much figured it out right away. When I figure out exactly what he found I'll fill you guys in. Thanks for all the help everyone!

[stealthee]

Yeah, I never would guessed that. Glad you got it fixed.