Help!! Battery grounded itself on hood
10-25-2018, 07:28 PM
#1
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Year: 1989
Model: Cherokee (XJ)
Engine: Straight 6 4.0
Help!! Battery grounded itself on hood
Aloha fellow XJ ers! I’ve been secretly following this forum for years, finally got around to registering. I hope to be able to contribute to the forum, you guys have helped me out so much.
So, the other day while driving down the highway I hit a super nasty pothole and the battery jumped up and made contact with the hood. Whole thing died. Positive terminal melted itself a bit. Towed it back home. Been trying to pinpoint the cause of the no start.
I currently have proper fuel pressure at the rail, new battery, starter is cranking away. Confirmed that there is no spark after pulling a plug and grounding it to the block. I’ve checked the fuses under the drivers dash and Nothing was blown. Horn, signals, all lights work. Here’s what I have replaced so far, all brand new:
-ECM (rebuilt one from oreilleys)
-Ignition Coil
-Cap + Rotor
-CPS
-Plug wires
-cleaned and checked grounds both at the dipstick and the braided wire one at the back valve cover.
I haven’t seen anything obvious or out of the ordinary, I’ve been checking all electrical connections and unplugging things for any sort of melted wire or short.
Any ideas? Are there any fuses I’m missing? I had a 94 and 96 before and they had a ton of fuses controlling all sorts of stuff. The 89 seems to only have three relays and the starter relay contraption in its place.
So, the other day while driving down the highway I hit a super nasty pothole and the battery jumped up and made contact with the hood. Whole thing died. Positive terminal melted itself a bit. Towed it back home. Been trying to pinpoint the cause of the no start.
I currently have proper fuel pressure at the rail, new battery, starter is cranking away. Confirmed that there is no spark after pulling a plug and grounding it to the block. I’ve checked the fuses under the drivers dash and Nothing was blown. Horn, signals, all lights work. Here’s what I have replaced so far, all brand new:
-ECM (rebuilt one from oreilleys)
-Ignition Coil
-Cap + Rotor
-CPS
-Plug wires
-cleaned and checked grounds both at the dipstick and the braided wire one at the back valve cover.
I haven’t seen anything obvious or out of the ordinary, I’ve been checking all electrical connections and unplugging things for any sort of melted wire or short.
Any ideas? Are there any fuses I’m missing? I had a 94 and 96 before and they had a ton of fuses controlling all sorts of stuff. The 89 seems to only have three relays and the starter relay contraption in its place.
10-25-2018, 08:24 PM
#3
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Year: 1989
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Argh...battery was free. Totally my fault, I just swapped over most the suspension and drivetrain stuff last week from my dying 94 and forgot to strap it down. Problem is fixed now, though damage has been done.
10-25-2018, 09:44 PM
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Been prodding wires and actually only found one fusible link underneath the dash, it checked out. Actually traced the wires all the way from the ignition coil to the firewall, all looked good.
tested the power to the ignition coil itself, it’s reading right around 12 volts. When the key is turned and the starter starts cranking, the output voltage remains the same however. Isn’t it supposed to increase?
tested the power to the ignition coil itself, it’s reading right around 12 volts. When the key is turned and the starter starts cranking, the output voltage remains the same however. Isn’t it supposed to increase?
10-26-2018, 02:19 AM
#7
Old fart with a wrench
I think your jeep is a Renix model, meaning it's got an older computer system in it. Give Cruiser54 a private message and see if he has any ideas to look for. It looks like your ground was good, LOL! I noticed the battery in my 2000 XJ is close to the hood, so not only is it strapped down, but I put a piece of lineman's insulated rubber mat over it.
BTW, I've been watching the action in Leilani Estates since May 5 thru Doing Hawaii and Apau Hawaii Tours. I hope you made it thru that okay.
BTW, I've been watching the action in Leilani Estates since May 5 thru Doing Hawaii and Apau Hawaii Tours. I hope you made it thru that okay.
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11-07-2018, 12:56 AM
#8
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Year: 1989
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Dude! That eruption was crazy sauce. Had a couple friends lose their homes to it. It took out some amazing natural wonders too, but also made a few in the process! The creation of the beach at Pohoiki in particular. Mind blowing what happened. Just camped out there last weekend.
Ok, so for the purpose of helping anyone in the future that has this problem, got it solved. It was a couple things really. Ironically, the battery seems to be perfectly fine.
1. The braided ground cable that goes from the chassis to the engine block was fried. Replaced that first.
2. All fusible links were fine. They are located immediately from the starter relay terminal on pretty much every wire that comes off of it. Looks like a long cylindrical rubber donut tube thing. Actually has “fusible Link” written on the wire. The only way I could figure out to check them was to cut the rubber thing off to expose the link itself. Taped em back up. As well, not a single fuse or relay was blown either, anywhere. That surprised me quite a bit.
2. The CPS was ridiculous. The original one wasn’t totally bad, but was measuring around 0.3 volts and the ~210 ohms so decided to replace it. Replaced it with one from oreilleys. Measured even less! Replaced it with one from NAPA. Measure around the same. Went BACK to oreilleys and got a second one from them. Finally measured 0.5-0.65 Volts.
3. My original fault was the mis diagnosis and measurement of the output signal to the Ignition Control Module. I ended up tracing the input from the CPS to the ECM (pins C1 and D1) and confirmed the voltage was getting to the ECM. Which, by the way, I replaced because I assumed it was fried. I then traced the 5 volt signal to the ICM, however I didn’t realize exactly what I was looking for. I thought the signal would be oscillating from 0 to 5 volts and my Volt meter would pick that up. It doesn’t pick that square wave up. A test light, however, did.
4. I then came to the conclusion that the Igniton Control module was receiving the signal to spark but was failing in this regard as I tested the ignition coil and it was within the operating parameters. Replaced the ICM and started up in about 3 seconds.
Lesson of the story: check your grounds. Check the ICM. And don’t trust those crankshaft sensors from the stores!!
11-07-2018, 02:05 AM
#9
Old fart with a wrench
Yeah, I learned that lesson the hard way also. ALWAYS spend the money and buy MOPAR for ANY sensors if you want to be sure they'll work and last a respectable length of time. YES, they go for a premium price, but you'll know what you're getting.
Case in point. The Mopar CPS is made with a neodymium magnet whereas aftermarket ones usually aren't. The Mopar one I finally bought would stick to a screwdriver. The other ones don't. The Mopar one came with a paper wafer on the sensing face for proper spacing from the flexplate and gets torn off on startup. Being a magnetic switch, it's important to maintain the right spacing. The oil pressure sensor on my WJ was leaking, so I changed it. When I took the old one off, the plastic part broke off. Inside was not just a diaphragm and resistor, but a pressure-sensitive crystal and a printed circuit! I've had to replace both the TPS and the IAC motor, both Mopar and both cured the problems exactly. All of these parts were original factory and had over 175K miles on them.
Case in point. The Mopar CPS is made with a neodymium magnet whereas aftermarket ones usually aren't. The Mopar one I finally bought would stick to a screwdriver. The other ones don't. The Mopar one came with a paper wafer on the sensing face for proper spacing from the flexplate and gets torn off on startup. Being a magnetic switch, it's important to maintain the right spacing. The oil pressure sensor on my WJ was leaking, so I changed it. When I took the old one off, the plastic part broke off. Inside was not just a diaphragm and resistor, but a pressure-sensitive crystal and a printed circuit! I've had to replace both the TPS and the IAC motor, both Mopar and both cured the problems exactly. All of these parts were original factory and had over 175K miles on them.
Last edited by dave1123; 11-07-2018 at 02:07 AM.
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