IRCM continues to blow

[jbserra]

Hey,

Well, if it weren't for this forum, I wouldn't have figured out that my IRCM was bad, BUT now I've killed IRCM #2 and am searching for the reason.

It *appears* that something is drawing too much current. The result is the traces on the IRCM circuit board pop like a fuse. I have tried 2 different IRCMs, replaced the fuel pump, and the inertia switch. The problem seems to always be related to the fuel pump circuit.

Should I just run a new wire from the IRCM to the inertia switch and then on to the fuel pump? Any amazing time saver troubleshooting techniques out there? Am I barking up the wrong tree?

I have had the car to 2 shops now, and I still seem to be the one who has to figure out this problem. The first shop tried to order me a new computer even tho it was fine, and the second said "I don't know where to go from here". Swell. So much for having someone else trouble shoot this. I was referred to an auto electric shop, but the guy just didn't instill any confidence in me that he would find the issue. Anyway. Bummed. Please help!!

Thanks in advance. AND as always I will give back ($$) to the forum if we figure this out.

-Jeff

 

[jbserra]

Well, the mechanic #2 says to check out fuseable links near the battery tray somewhere. Should I put any stock in this diagnosis?

 

[Redline]

IIRC the radiator fan relay is also in the IRCM along with the fuel pump relay. Check your radiator fan to make sure it works ok and isn't drawing the extra voltage because its starting to freeze up or something.

I don't know anything about fuseable links???

 

[SHOZ123]

You could use another external relay for the fuel pump and take 99% of the load off of the IRCM. First I would test the amperage draw on the fuel pump though.

 

[projectSHO89]

First, I'd crack open the IRCM and see exactly which trace is burned so you know which exterior circuit is shorting out.

Schematics including the IRCM are available for download. Look for a sticky in the "How do I...?" forum.

Steve

 

[jbserra]

Thanks Steve.

Anyone know how much current the fuel pump should draw?

I will crack open the IRCM this weekend. I'm assuming it's on the power to the fuel pump trace, but I will confirm. I'll probably be running a new wire...

Thanks!

 

[SHOZ123]

It has a 30A fuse. Maybe a larger one has been put in it's place?

 

[jbserra]

As far as I can tell, doesn't the output of the relay go straight to the fuel pump and EEC? The relay continues to work, so I don't think it is the control part of the circuit. I don't think there is a fuse on the switched power part of the circuit, unless you count the trace on the IRCM. The $200 fuse shall we say...

The power no longer gets to the fuel pump because it burns up that trace that goes out the box. I am going to confirm this soon, but I'm pretty sure.

http://shoforum.com/diagrams/1992/9207.pdf

 

[SHOZ123]

Correct, the only thing between the IRCM and the fuel pump is the collision switch in the trunk. Still the fuse protects the entire output circuit of the fuel pump relay.

On the Gen 3s some have had a problem with the wires inside the tank chafing and shorting out.

 

[jbserra]

The trace connected to pin 10 and 12 are fried. 12 makes sense, but according to the diagram, 10 isn't connected to anything. I look at my box and it has a relay attached to it...

So, I guess it isn't isolated to the fuel pump circuit...

Help!

 

[jbserra]

Ok, tracing the circuit, it looks like 10 and 12 are BOTH inputs to what becomes pin 5 for the output, which is the pink/black to the fuel pump. Whew, that seems somewhat consistent with what I was thinking earlier.

So I took an ohm meter and checked pin 5's resistance to ground. It was only like 30 ohms. I disconnected the inertia switch, and the resistance jumped to 3k ohms. I connected the inertia switch, but disconnected the run to the fuel pump, 3k. I plug it back in, 30 ohms. So, somewhere from the inertia switch to the pump. I check the lead to the pump to ground and nothing unusual. I check the fuel pump plug connector to the wire, looks good. THEREFORE, must be the wire from inertia switch to the plug on the fuel pump. I disconnected that run, and used a jumper cable instead, 3k! Will rerun the wire tomorrow. God, I hope that is it...

 

[jbserra]

Box fried again. Same traces, new spots. aow35890)%()#($@!!!

I took it out for a drive, and revved it up and it wouldn't hit higher RPMS. I'm guessing it not enough fuel. It bucked like mad. Then it died.

If I hook power straight from the battery, through a switch on the dash, to the inertia switch to the fuel pump, how soon until my battery explodes?

-Jeff

 

[SHOZ123]

The short could be inside the tank. Be careful.

 

[jbserra]

I'm giving up. Car's for sale. Make me an offer. It's near Milwaukee, WI.

I'll put a post in classifieds within a couple days.

 

[matt621]

did you ever figure this out? I have the same problem...

 

[jbserra]

did you ever figure this out? I have the same problem...

No, I didn't. Bluestreak has my car now. They plan to get the car running again. She should give me an update once they find the problem.

 

[Bluestreak]

Yeah, I'm working on it. The SHO is a wiring nightmare and I haven't had a whole bunch of time to dig in it. This comming Sunday, I'm planing on spending a few hours on it.

 

[FamilySHO]

For what it's worth I had the same problem. After blowing one IRCM the shop that had the car put in an online fuse on the hot lead to the IRCM. They examined the wiring back from the IRCM and found a wire was chafed. They put some electrical tape around it and gave me back the car with the in line fuse. The fuse has never blown and I haven't had a problem since.

 

[zuup_2000]

Do you know which wires from the ircm were chafed?

 

[FamilySHO]

No. The information was based upon was told to me. I took a look and the wiring hadn't been unwrapped very far from the harness. I didn't look further: 'let sleeping dogs lie'. I note that the IRCM fule pump relay had gonr the year before from a bad ground and I recently had replaced thge cooling fan. This reulted in the plug being removed and wiring moved about a number of times. The car's a '92. Wiring insulation subjected to the extremes of hot and cold probably doesn't get more flexible with age.