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cps grounded out, need advice

mjdriver

mjdriver

NAXJA Member #1376
Location
Myrtle Beach, SC
So my truck did start, cranked but no start. I thought cps right away since I haven't replaced in 8 years. I found the rear engine ground strap laying across both cps wire and the conecter, all melted. there was definatly contact between the red cps wire and the engine ground, anybody know what other problems that could cause. for the record non of my gauges work when I turn the key
 
R&R the melted wires and sensor. Try again. Rarely does it blow the computer.
 
I was more conserned with the damage if any it would have caused. where does the cps tie into up the line, what fuse or breaker does it have.
 
check your battery to engine ground cable at the dipstick tube for a good connection. If it has worked loose of corroded, the ground strap on the cylinder head will act at the primary ground and can get very hot flowing the excess electricity that's supposed to flow from the other location.
 
shorty thanks, I will check that.
another thing the last couple of time I drove it before it didn't start the volt meter was running really low like 8 or 9 volts while running down the freeway. your idea on checking the grounds sounds like a good one.
 
replaced CPS, cleaned , grounds at the battery to block (dipstick tube), block to fire wall, cranks over but no fire, have not tested for spark, I gotta find a nieghbor to come over and turn the key for me. fuel pump primes and I have pressure at the rail. I took a plug out and couldn't smell any fuel on them. and all the gauges are dead, they don't move at all. I checked all fuses and the relays.

can you guys help me with a list of things to check.

the dead gauges have me worried.
 
mjdriver said:
replaced CPS, cleaned , grounds at the battery to block (dipstick tube), block to fire wall, cranks over but no fire, have not tested for spark, I gotta find a nieghbor to come over and turn the key for me. fuel pump primes and I have pressure at the rail. I took a plug out and couldn't smell any fuel on them. and all the gauges are dead, they don't move at all. I checked all fuses and the relays.

can you guys help me with a list of things to check.

the dead gauges have me worried.
Click to expand...

That 8-9 volt thing has me concerned. You could be in the position of having enough amps for cranking but insufficient voltage, 9+, to let the electronics operate.

Are talking about the MJ in your signature? Really doesn't matter, I guess.

First thing, charge the battery overnight (good) or for 24 hours (better).

Make sure all the cables are good, in other words check them with an ohm meter for resistance.

Once the battery is charged have it load tested. If it passes, hook it up and give it another try.

Check the gauges fuse in the fuse box.

Post back with results.
 
I don't have access to a charger,

I have 2/0 welding cable battery cables that are in good shape.

what should the resistance be?

the battery was at 10 volts so I jumped it with my other jeep. it cranked good and strong kept tuning the engine but no start.

gauges fuse is good. that was the first thing that came to me.

where does the volt meter gauge get its reading from?


O.T. joe I used to be stationed out at brookings, I loved that area, pretty country views
 
Last edited:
mjdriver said:
I don't have access to a charger,

I have 2/0 welding cable battery cables that are in good shape.

what should the resistance be?

the battery was at 10 volts so I jumped it with my other jeep. it cranked good and strong kept tuning the engine but no start.

gauges fuse is good. that was the first thing that came to me.

where does the volt meter gauge get its reading from?
Click to expand...

Resistance should be near zero, sounds like you have good sized cables, but check them with an ohm meter.

If your static voltage is below 12v, and you put a load on the battery, even when jumping, you may still have problems. Pickup a Wal-Mart charger, or borrow one, or take the battery to a shop and have them slow charge it (fast charge = surface charge).

The voltmeter is tail-end charlie in the circuits, instead of reading direct battery voltage it is reading what is left over--that is why the bigger the load the lower the gauge reads.

What about the rest of the cabin electrics? interior lights, radio, etc., are they working?
 
interior lights work, no radion in it to test,

battery right now has 10.8 volts

cps was getting 3.8 volt

I have never had a ground wire from battery to fender, should I?

I have the 88 cherokee electronis manual, that I saw there was supposed to be a ground coming out of the wiring harness at the fire wall but mine doesn't have one.???

How do I test the computer?
 
Hallo.
A good battery has at least 12.5 Volts.
To have a short ground cable from the battery to the fender is advisable.
The ground strap of the engine block to the firewall should be checked with a DMM with Ohms. Corrosion can be the problem with the contacts.

wim
 
Last edited:
wim,
I looked at your other pics, you have a second ground cable from the fire wall to where?

I wire brushed all the battery cable and ground straps that I have.
 
Renix normal grounds are batt to block, harness to dipstick tube, back of head to firewall (usually a flat braided cable--POS), there is a ground from the starter relay either to the fenderwell or NSS. There are other grounds but those are the big ones.

Still not happy with the voltage, your battery needs attention.
 
on my 89, there is also a ground coming from the main wiring "cluster" near the brake booster and goes through the firewall. the ground comes from from the cluster and attaches to the fender in front of the window washer fluid tank.
 
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