So I am doing a S4 PFC conversion with my TII. Bad news is today while checking for fuel lines for leaks(run a hot pump so I needed battery power for 12V switch), my upper intake manifold slide down and touched the HOT wire on my alternator and caused a big spark( I was being ******* lazy and didn't want to re-zip tie my vac lines) . Big enough to cause my main 80A fuse to blow. I was worried about my PFC so I went to check if it operated.... NO GO.

First off I never got to check if my PFC worked because I was still working on the engine. BUT when I went to check if the unit was OK after the Boo Boo, once I turned the ignition ON, my datalogit red light was lumminated but no commander was lit up.

Problem is one of my four fuel injector resistors is getting very hot when the ignition is cyced to ON. It is wire 3E on the harness. The Power FC commander wont light up and I know the resistor doesn't get that hot. Why is it so hot? I need to check the injector grounds for continuity BUT until then any ideas? I assume it is a short but where?

I hope to God I didn't fry it.

any help is appreciated and I feel like a complete *** for doing something so ameatur

thanks guys.

 

This is just blind internet diagnosis, but you may have a few non PFC-specific problems. It's possible that blowing that fuse didn't do anything at all except blow the fuse, and these problems were already there (since this was the first time you turned the ignition power on during the install right?). You may also find more help in the 2nd gen forum considering that more people here are FD guys. Now have you tried plugging the commander directly into the PFC as opposed to into the commander port on the datalogit? The fact that your datalogit red light works is a good sign. When you get your laptop set up, see if you can connect to the PFC and read the map.

The resistor could be getting hot because of a bad solder joint or something that is causing high resistance which heats the wire up when it gets current--which means it could be unrelated to you blowing the main fuse. If it had a short I would think you would've blown your EGI Comp fuse (the one on the end of the fuse box, whatever it's called) I think. That would result in the ECU not getting power and neither would the datalogit. I shorted the 0-5v feed wire to my stock pressure sensor (black/white) and it blew that fuse.

Open up your factory service manual wiring diagram and look at pages 50-14, 50-16, and 50-22 . The alternator on the s4 turbo cars is on the "engine" harness according to the FSM (harness "E" in the diagram) and the fuel injectors are on the "emissions" (EM) harness, the one that most people actually refer to as the engine harness. That may not mean anything, but it seems like the main fuse or the EGI Comp fuse would protect the fuel injectors from something like that.

 

That is what I figured about the main fuse. I doubt any stray voltage went beyond the fuse.

I did try to connect the commander directly to the PFC and no illumination. Then back to data logit and no light or commander illumination.

I am thinking maybe I have a shorted inj harness clip OR the grounds are bad and am going to trouble shoot on Fri. I did do some tinkering and when I wiggle the resistors when power is applied I can hear the injectors clicking intermittently. The resistors ONLY get hot when the harness is connected to PFC. When the ignition is ON and no harness connected to PFC the resistors are not hot.


I hate side tracks like these when you get so close to being finished.

 

So I checked continuity on all injector grouds and 12v wires and they were good.

-My four resistors all checked out good @ 10 ohms each.
-Each fuel injector wire put out roughly 12.17 volts when ignition is ON.

I did find this though: I decided to check my impedence on my secondaries and they checked out good at 4.5 ohms BUT my primaries are down to 2.3-2.5. I SWEAR when I checked them a year ago they were around 4 to 5 ohms.

Can injectors fry? could this be the route to the problem. The resistor that gets hot is a primary injector wire.

Kinda stuck from here because wires check good. hmm?

 

is your commander brand new or did you get it used? You can send the PFC in to see if it's ok. Or you can just try to start the car like nothing happened.

Cut the resistor out and replace it. You using the radioshack ones? they aren't expensive. Install the new resistor, twist the connection together, but don't solder it yet. Turn the key to the on position and see if it heats up first like it did before. When you do solder it again, don't use too much, just make sure the joint is heated up (you're not dripping the solder on there are you? heat the wire first and let the solder flow into the joint a bit) and there is a light coat of it on there, not a thick glob.

What brand are your injectors? The Bosch ones are usually closer to 5 ohms. 720 injectors can range depending on the brand. You may just be seeing phantom problems dude. It's easy to get into that mindset when you make a mistake and you think you blew something up on your car. Trust me, I've been there. I ended up replacing my emissions harness because I had hacked up the wiring so bad when I didn't know what I was doing.

 

If you can hear the injector clicking when you wiggle the wire, then you are grounding the injector. The PFC actuates the injector by grounding it, if there is a constant ground then the injector stays open. This will over heat the injector and the resistor. You should not be able to actuate an injector by wiggling a wire.

Next time you email me for tech advice include the parts where you blew the main fuse, withholding important info makes it more difficult for me to be able to help you.

 

If there is a constant ground, where is it? I have not altered the wiring harness or added additional grounds. Could the PFC not function of there is a grounding issue like this?

 

It can only be in the engine harness, if it clicks the injector when you wiggle the wires. Check the terminals in the connectors.

Did you buy the PFC used or new?

 

I purchased it used from a 3rd gen member here. I am heading out right now to further trouble shoot.

 

So I plugged in my factory ECU to check to see if the resisitors did the same thing.... not a damn thing. Resistors stayed cool to the touch.

I have contacted apexi and am going to send the unit in for a bench test. I explained the problem and they will let me know if anything is wrong+ fix it for hopefully not too much.

At least this will give me some progress since I never really checked to see if the unit worked, i just assumed it did OR maybe it did fry during to firework display. I dont know.

Everything else on my wiring harness checked out good and I can't find a damn thing wrong.

 

most times when I buy used electrical parts I regret it (I would never buy a new exhaust though)... I got my PFC brand new for $805 shipped from the FDNewbie group buy a year ago. Took like two months though. Datalogit was also new.

 

Well I don't think he would have sold it to me broke but a sucker is born everyday. We will see once Apexi gets back to me. I really hope the unit is fine and the problem is on my end BUT then again I have almost checked for everything in the harness and don't know where to go from here.

Anybody know what are the symptoms for fried fuel injectors?

 

Little update; I sent out the unit to Apexi this afternoon. I also decided to get a hold of my old F-CON I ran before the upgrade. Plugged it all in and tested to see if the resistors got hot. Thay DID NOT so that is two ECU's that do not heat the wires and resistors. I will see what Apexi has to say about the unit and I am starting to think the PFC was bad OR I did fry it. Bummer!

 

Well I have officially tested/inspected every possible wire associated with the ECU that could have possibly caused issues with the PFC. Everything is within spec and I even opened up my whole engine harness(just re-wrapped it with new insulation) to check for melted wires.

apexi got it yesterday and are testing it as we speak. They told me if it is in fact bad that it is a 3-4 week wait from going to and from Japan. I may be able to expedite it a bit faster but it will cost me.

 

ive ohmed lots of s4 injectors and they are supposed to be about 2.5 ohms. i think that is in factory service manual. most turbo cars "em" harnesses are in really bad shape these days. the heat frys the insulation on the wiring and if the harness has been moved enough the insulation will break down and leave wire exposed. usually same spot on gnd and power wire, so that may be some of your trouble. also i have put s4 motors in s5 cars and vice-versa but the ecu pin out is not the same. the end of the "em" harness where it plugs into the power fc, are you sure wire for wire is correct? also i had alot of trouble working with wrong commander pn's, are you sure you have correct one? I have a chart that lists s4/s5 pin numbers. if that would be of help i'll post or something.

 

Thanks man but i have a S4 and have owned the S4 FSM since I have owned this car for 7 years. They are the right wires because I rewired the EGI ground leads a year ago to solve some hesitation problems when running my F-CON. Plus my 1988 was a high impedence system, there was a split for S4's between high and low. I can't remember what year the split took place. Regardless my primaries are aftermarket 720cc. My FC is far from stock.

As for the EM harness I ripped into it last week and the wires were in very very good shape. Not brittle at all(still very flexable and soft), just the black insulating wrap that made the "body" of the harness was crispy.

I am very sure that I fried the PFC. It blows but that is what I get for being lazy and non-attentive. Two good ECU checks/ and troubleshooting settles my assumption that the PFC was NOT bad to begin with.

Plus Apexi is taking their damn time bench testing it. They got it monday morning and still nothing. Hopefully next week.

Thanks for the concern though.

 

So, I was contacted by Apexi today and the PFC is......Good! ?????

I am officaily stumped and angry. I was almost positive that with my other two ECU checks that the PFC was fried. It is GOOD news that it doesn't need repair just a headache on my end now. The Bench test was performed twice by Kieth at Apexi just to make sure they didn't miss anything.

I guess when I get it back I will plug it in and IF it heats up again , back to troubleshooting.

I am stumped because I have checked everything. I will try another EM harness next. Shitty.