Author Topic: why did my car take a crap? (Read 9148 times)

Blip Bavarian · « **on:** June 11, 2009, 02:54:35 PM »

My car will not start. I think that the biggest clue is that the CEL doesnt illuminate at all. I checked all relays and fuses in the fuse box and along the fire wall. All relays and fuses passed the test except.....The main relay (DME relay) did not pass the test. I applied power to 85 and 86, and then checked 30 and 87 with my multimeter. when i applied 12v of power to it, it did not click like all the other relays, also, the multimeter showed no continuity between 30 and 87.

I thought great. just get a new realy and voila.... Today i got my new main relay, and tested it. It did the exact same thing as the original "fried" relay. No click, and no continuity. I plugged it in, and still no CEL light. anyone know why the continuity test doesnt work on the main relay???

Here are my other symptoms
- No CEL ( cant do stomp test) My CEL used to work fine
- No buzzing from ICV
- No buzzing from fuel pump.

I have done a complete hose swap, and have cleaned out my sensors with contact cleaner.

I have been searching for other possibitlities of what the issue could be, and am left with 3 questions.

1 I have read that the ECU/DME may not be getting power. However, I do not know how to check this with my multimeter. Can someone please explain how this is done, or post a link.

2 Also i have read that it could be a bad connection at the fusible link. Once again i do not know how to check this.

3 Third i have read alot of people having issues with their CPS. I dont think that this is the case, b/c i dont think that that would knock out my CEL light... not sure though. Once again, I am not sure as to the proper pprocedure for checking this with my multimeter, and need help

Im sure there are other possibilities for the failure that i am unaware of. If you guys can help wuide me on how to thest the DME, CPS, and fusable link; That would be fantastic.

DesktopDave · « **Reply #1 on:** June 11, 2009, 05:01:19 PM »

I'd think fusible link. I don't know why it'd cook, but it's not too hard to check it out. I've only done this on a 325is, so YMMV:

Pull up the carpeting in the trunk, look on the right by the wheel well. You'll see a plastic conduit held in with 2 or 3 plastic nuts covering the positive wires heading to the front. Get that conduit off and look for the small positive wire.
You'll see it has some heat-shrink tubing on it, cut some of that away (maybe 4-5 inches) until you find a large bulge in the middle of the wire. That will have more heat shrink tubing...cut that away too.
You'll be able to inspect the fusible link there, it's a little square PCB with one fat trace on it. It's all riveted together, so you'll have to re-wire if it's bad. I just used a small nut & bolt and lots of electrical tape to fix my old 325is, but the car was so rusty I didn't care about it much. I think it's rated 80amp, so plan ahead accordingly.

DesktopDave · « **Reply #2 on:** June 11, 2009, 05:11:11 PM »

I've always tested the DME by looking for the check engine light. If that's not on, you know it's either burned out or the DME isn't powering it up. You are right...even if the CPS is bad, the check engine light will still work and the DME will still fire plugs. It just won't pump fuel.

The CPS can be tested by pulling the lower connector on the wiring plenum toward the front of the engine:

It's in the middle of the picture...click to see a larger version.:cool:

Switch your handy meter to ohms, test pins 1 & 2. Should be 680ohms, give or take 10%. At least that's what I've heard...just tested mine at 580. I had to clean the sensor once...it was encrusted with oily residue from my leaky front main seal (replacement is planned) and I suspect the dirt was mostly metallic...no magnetic signal means no fuel pump signal from the DME.

Blip Bavarian · « **Reply #3 on:** June 11, 2009, 05:28:11 PM »

Okay, so this leaves me to believe that it is probably the DME, since im getting no CEL. Do you know how i can test it with the multimeter to see if it is getting power? What setting should my multimeter be on and where do i place the probes?

i would rather check that the DME is getting power before i start pulling the shrink wrap off the fusable link...

It is curious that all this happened as when i did the hose swap...

as always, thanks DD for the advice. I really appreciate it.

DesktopDave · « **Reply #4 on:** June 11, 2009, 05:43:29 PM »

I found this advice for a 325, but ours should be the same:

Quote

http://forums.bimmerforums.com/forum/archive/index.php/t-1206661.html
For the DME to run power must be present on DME connector pin 27 (Start input), 18 (Unswitched power) and pin 37 (main relay output). The Start input is supplied from the ignition switch and when present causes the DME to engage the main relay and power up the DME. A problem with any of those or the main relay would result in the engine drop outs, a flash of the CEL, and no codes.

I can't think of another way to test the wire without taking it apart, unless we can find it and isolate it for a continuity test.

Blip Bavarian · « **Reply #5 on:** June 11, 2009, 05:50:14 PM »

any advice on how to locate pin 27, 18, and 35?

then i assume i do some sort of an ohm test...?

DesktopDave · « **Reply #6 on:** June 11, 2009, 06:13:04 PM »

Nope, you'd just test to see 12vdc on the DME pins.

I think you could use a LONG set of leads to do a continuity test on that positive wire. I'm not 100% sure this will work, but it's pretty painless. Here's pics of both sides, click to enlarge:

See the small black wire? Unbolt that. Attach a wire as a testing lead from that to your meter and only to your meter...make sure it doesn't touch anything else because it'll weld itself to anything metal if the fusible link is good...:eek: Go to the trunk.

See that battery terminal? Put the other meter lead on that and test for continuity or voltage. I've also circled the troublesome fusible link. It's easy to get to.

Blip Bavarian · « **Reply #7 on:** June 11, 2009, 07:11:47 PM »

DD, if i followed your instructions correctly, there is no continuity.

here is what i did. i attached a jumper from the positive terminal of the battery to one probe of the multimeter. Then i disconected the small wire that you show in your picture. I connected a jumper from that wire to the other probe of my multimeter. with that connected i showed no continuity.

The key was in the off position for the test....

ive got an idea...
i also have a secondary 12v source. if i used a jumper and connected the positive side of the 12v source to the small wire in your pic, would that power up the ecu??

DesktopDave · « **Reply #8 on:** June 11, 2009, 07:19:13 PM »

Pull the insulation and fix the burned out fusible link. Like I said, I used a small nut & bolt I had laying around and taped it all up well. You don't want a short there.

If you wanted to do a professional job, you can probably get that part at the dealer. Alternatively, go to an auto parts shop and pick up an inline fuse holder. I'd guess that it's a 10 or 15 amp link. It's wide but very thin. I also heard someone joined it with a trail of solder.

Blip Bavarian · « **Reply #9 on:** June 11, 2009, 07:35:14 PM »

i just opened up the fusible link. I pulled all the shrink wrap off. It looks like metal at both ends with a rubbbery center section. when i tested for continuity from one metal end of the fusible link to the other (across the rubbery gap), there was no continuity. is my line of thinking correct? there should have been continuity right?

i guess you are right. this is the problem.

i tried to test it by attaching a small jumper with small clips at each end to eaither end of the fusible link. Therefore connecting it? then turn my key to half position.... the CEL did not light up. I went back to the trunk to check on it, and there was a little bit of smoke in the trunk. The rubber on the little jumper was melting. i unhooked it and it sparked, and the jumper was really hot with melting rubber.....

needless to say, the CEL did not come on.

DesktopDave · « **Reply #10 on:** June 11, 2009, 08:23:13 PM »

Well, you know half the problem...the fusible link should have a little metal strip going across that center section. Now you just have to find out where the short is. There is no way that the DME is pulling that much power.

I'd guess that there's some insulation rubbed off that wire going through the frame somewhere, since it didn't blow a fuse in the box. You could test that for continuity to ground when it's off the battery...just test to any good ground on the car. If you get continuity, then you'll have to check that whole wire. It runs alongside the passenger side frame, between the seat and the door frame. The seats come out easily, four big bolts.

Blip Bavarian · « **Reply #11 on:** June 11, 2009, 09:11:04 PM »

Quote from: DesktopDave;73493

Well, you know half the problem...the fusible link should have a little metal strip going across that center section. Now you just have to find out where the short is. There is no way that the DME is pulling that much power.

I'd guess that there's some insulation rubbed off that wire going through the frame somewhere, since it didn't blow a fuse in the box. You could test that for continuity to ground when it's off the battery...just test to any good ground on the car. If you get continuity, then you'll have to check that whole wire. It runs alongside the passenger side frame, between the seat and the door frame. The seats come out easily, four big bolts.

when i had the small jumper bridging the link, i turned the key half position. i didnt get a CEL. Then i tried to crank the car. I think that when i tried to crank it is when the jumper got hot and began to melt the rubber.

I was just using small guage hook up cable from radio shack, which im sure was not sufficient.

i do have the strip of metal on the link. It is broken in half. When i did the hose swap, i didnt disconect the battery. Maybe that is when the link blew....

also if there is a short, would it have to be in that main wire? Or is it possible that it could be anywhere. I have some exposed wires hanging out where my stereo used to be. My car is completely gutted, so it shouldnt be that hard to find an exposed piece in the main wire if there is one.... if i find an exposed piece what do i do? just wrap it in electrical tape?

DesktopDave · « **Reply #12 on:** June 11, 2009, 10:02:54 PM »

It's hard to say where the short is. I'd suspect that there is a short in that wire from the battery to the DME. I'd say it's chafed in the rear seat area, where it runs through the seat back. Might also be chafed in the front of the car, coming through the firewall. I'm thinking that it just took a while for the vinyl to melt, while you were cranking the car it was long enough to get hot. Cheap metal has high resistance...that's why they use such high-grade copper and insulation for auto wires.

I'll bet you have no other blown fuses...but check to see if I'm right. If so, it has to be in the battery harness...there are no other unfused wires in the car. The stereo power wires run through the fusebox and the speaker wires use a 'floating' ground that goes directly to the speakers...so it can't be them.

If you do find torn insulation just fix the cause and wrap the wire in some electrical tape. It won't need a whole lot of insulation, one or two layers. It's just important that it's covered. Those positive wires can carry a lot of current...especially that big fat primary positive wire...make sure it's intact and happy.

IMHO it didn't burn out when you did the hose swap, unless you doused the DME.

Blip Bavarian · « **Reply #13 on:** June 12, 2009, 12:06:30 AM »

I will check all of the fuses tomorrow, and then i will look for a chafe in the wire. hopefully i can get the issue resolved this weekend. My gf is gonna kill me if i spend any more time in the garage.

i didnt douse the dme at all during the hose swap. it just seems strange that the car would crank, and the stomp test showed a vacuum leak before the swap, and then when i put everything back , and it wouldnt crank. i guess it could be unrelated.

Thanks so much for all of your help Dave. I probably need some more advice on how to repair/replace/rig my fusible link....

here is a pic of an inline fuse holder. Is this what you are talking about using in place of the OEM fusible link??

If so, what would that entail?

DesktopDave · « **Reply #14 on:** June 12, 2009, 07:10:16 AM »

Yeah, I'd get something like that...with an assortment of fuses. I can't find good info about the rating of that fusible link, but I've seen 20amp, 30amp & even 80amp. If I had to guess, looking at how thick the smaller positive wire is, I'd start at 20 amps and work my way up.

I don't know what to tell you about the GF. I use the car as marriage therapy...I can keep myself from annoying my wife while I'm working on the car.

I'd also clean the wires with some flux & solder that sucker in with a setup like that one above. Or just use a nut & bolt with some electrical tape...idle it for a while and see if it melts. What's the worst that could happen?:rolleyes: