Ok. The car is an 84 Z28 L69 305HO 5spd

RECENT REPAIRS/MODS:
1. Swap to serpentine belt (replaces all accessory pumps, alt, etc)
2. As a result of #1, Alternator was wired backwards for 2 days. Wiring fixed, normal voltage.
3. Took carb off to adjust Mixture Control solenoid. (Done with proper tools, adjusted to 4/32" travel)
4. Adjusted TPS to 0.48 volts with DVM
5. Replaced Oil Press Sender (problem was occuring before this)
6. Fixed wires to Coolant Temp Sender (looked like they were shorting out)

Twice since the serpentine swap and alternator fiasco the ECM/IGN fuse has blown while I was driving. No Obvious reason.

Today I replaced the oil press sender and adjusted the TPS. I fixed the CTS wires because right at the connector, they were bare wires for about an inch. Started it up and after about 4 seconds, the ECM/IGN fuse blew yet again.

I have the shop manual and the only things I can see on that fuse line is the following:
1. EGR solenoid
2. Mixture control solenoid
3. Coolant Temp sensor
4. Air diverter valve
5. Air select valve
6. TPS
7. Vacuum sensor
8. O2 sensor

So far I belive I have ruled out the M/C solenoid, TPS, CTS, and O2 sensor (no obvious wire grounds)

Any one seen this before or have an idea???

Oh also, the ECM is fine. I've swapped it with my 84 TA (swapping the prom also) and I can scan it no problem with the Auto X-ray.

I need to get this running right before tomorrow hopefully.
Thanx


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Randy
84 Trans AM LG4, 700R4 T-tops
1984 Z28 L69, 5 Spd, T-tops
"Don't sweat the petty things...Just pet the sweaty things"

 

There could be a short in CKT 419 ( I think...at least that's what it is in 89) or the ignition itself. Did you try putting in a higher rated fuse and then tinkering with stuff to try to blow it? That kind of thing can be a nightmare. If you have a shop manual pull the ecm harness and start testing circuits. Not sure how you'd test the ignition, but it would be in the manual somewhere. Are you SURE the cts is in good shape and wired correctly?

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Base: 89 Iroc-Z LB9 auto 2.73 posi
Exh: 3" Dynomax muffler, 3" Pipe in place of cat
Ign: GMPP 8MM wires, Accel cap&rotor, AC Plugs
Fuel: Cleaned and flow-matched injectors, afpr, !air pump&diverter valve
Sound: Clarion deck, Kicker speakers and amps
Suspension: KYB Shocks, BMR Strut Tower Brace
Misc: TB Bypass, Synthetic Oil, Flexlite Transmission cooler,
free mods, flow tech headers on the way,
engine swap and 4th gen seats in the works...

 

Ok, Just replaced the CTS because I thought it might be bad from the wires shorting before.
Results: Fuse still blows 2 seconds after starting the car. (Although the newer weatherpack connector on the CTS is nice. hehehe)

I do have the shop manual and I don't know what CKT 419 is. On mine, the main circuit coming from the ECM/IGN fuse is 439.

I haven't tried using a higher rated fuse because I don't want to damage something else further down in the circut.

Right now I'm stuck digging through the Shop Manual and trying various things.
Anyone got any other ideas to try?
Randy


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Randy
84 Trans AM LG4, 700R4 T-tops
1984 Z28 L69, 5 Spd, T-tops
"Don't sweat the petty things...Just pet the sweaty things"

 

WC,

While running in "limp home" mode, what is teh system voltage?

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Later,
Vader
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"Make Me Bad..."
Adobe Acrobat Reader 4.0

 

The voltage was approximately 13.5 to 14 volts. Seems like the Alt. is charging fine so far.

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Randy
84 Trans AM LG4, 700R4 T-tops
1984 Z28 L69, 5 Spd, T-tops
"Don't sweat the petty things...Just pet the sweaty things"

 

One thing. When the Alt. was wired backwards for the 2 days, voltage was close to 15ish amps. I believe this was because the regulator wasn't functioning right (due to the wires being swapped)

The problem never ocurred before the serpentine swap/Alt fiasco.



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Randy
84 Trans AM LG4, 700R4 T-tops
84 Z28 L69, 5 Spd, T-tops
"Don't sweat the petty things...Just pet the sweaty things"

 

Well I didn't get a chance to look at it today since I was at work from 7 am to 8 pm. Althought I did try to start it this morning....
It sucks!!! Right as it starts, the motor sounds great, then 2 seconds later the fuse pops and it sounds like crap.. LOL
Hopefully I can leave work early tomorrow to look at it.

I think my next step is to take the components that come off the ECM/IGN fuse one by one and try to start it. If the fuse doesn't pop, I should have found the culprit.

Aren't Electrical problems wonderful???


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Randy
84 Trans AM LG4, 700R4 T-tops
84 Z28 L69, 5 Spd, T-tops
"Don't sweat the petty things...Just pet the sweaty things"

 

This sounds like the same thing that happened to me once. do this put in the fuse but turn the key to where you get power but don't start the car and see if the fuse blows. if it blows that means that your ecm is grounding it self out. some wire is touching a picece of metal. the same thing happened to me and i found out that i had a short in a circut.

 

Well I finally figured it out. hehehhe

During the swap, the AIR valve assembly wouldn't bolt into it's normal location due to the new serpentine bracket & AC compressor.
I had moved it back and set it loosely in. The smog pump wasn't connected to it.
Well apparently the lower electrical connection ended up resting on the exhaust manifold, melted, and produced the fuse blowing.
I removed the AIR valve since it's not hooked to the smog pump anyway and VOILA!! no more fuse blowing. hehehe

Thanks guys. At least it was something simple, even though I missed it in my first search.


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Randy
84 Trans AM LG4, 700R4 T-tops
84 Z28 L69, 5 Spd, T-tops
"Don't sweat the petty things...Just pet the sweaty things"