Validate my Diagnosis

Hey all,

I was supposed to help a friend move today, I hopped in to the truck ('87 MJ, BA-10, 4.0L) and no start, not even clicking, and the volt gauge reads a smidge under 12V. I called AAA out for a jump since the only other car was blocked by the truck. He comes out and hooks a booster box up to the battery terminals and still nothing. In a fit of genius we decided to hook the positive lead directly to the lead for the solenoid (The wiring is a little shoddy and there was enough exposed wire to get a connection) and still no start and no clicking. To me this sounds like I need to pick up a new soleniod, Do you all agree?

Thanks in advance.

Pat

Check your grounds (specifically where the negative battery cable connects to the engine block). I had a similar problem on my '91 XJ, and it turns out the nut had worked it's way loose over the last couple hundred thousand miles. After cleaning up the grounds and tightening the nut, it's running and starting much better than it was before.

Good idea, the grounds are tight (Haven't checked - to block yet), however all the exposed grounds show some signs of oxidation (I'm referring to the cables that look to be braided) as they've a bit of a greenish tinge to them. The only thing that makes me question that is that all the light's, guages, stereo, etc.. function with the key in the on position. I would think that if there was a grounding issue those wouldn't function, but I've certainly been wrong before!

I'll head out there in a couple of hours when the temp here drops below the century mark! Thanks for the tip!

Pat

Possibility it could be the keyed cylinder...my 89' XJ did the same thing....was getting really hard to turn....pulled strng wheel lockplate swapped in one from AZ...hit key pow...started.
Had taken alternater,starter,and battery to AZ and had all 3 checked...IF you can put it in neutral and it starts,then your talkin NSS ....Which ain't cheep at all.....The NSS CAN be cleaned and put back together....
look here...
http://jeepin.com/features/nss/index.asp

I thought only the automatics had a NSS. Was I wrong? I'm not having any difficulty turning the key in the ignition, and the entire column was replaced somewhat recently. It's worth checking if all the grounds check out.

Pat

Start by checking for power at the starter trigger wire while a friend holds the key in the START position. If you've got power there, check the power and ground leads at the starter. If all is well, replace the starter.

Phager said:

Good idea, the grounds are tight (Haven't checked - to block yet), however all the exposed grounds show some signs of oxidation (I'm referring to the cables that look to be braided) as they've a bit of a greenish tinge to them. The only thing that makes me question that is that all the light's, guages, stereo, etc.. function with the key in the on position. I would think that if there was a grounding issue those wouldn't function, but I've certainly been wrong before!

I'll head out there in a couple of hours when the temp here drops below the century mark! Thanks for the tip!

Pat

Click to expand...

That's what had me fooled. The battery grounds into the body and the engine block, with the engine block ground being a much larger wire. Many of the accessories ground out to the body, or don't draw a whole lot of power. However, the starter draws a huge amount of power when it's running, relative to other electrical components, and it also does not have a ground cable (at least on my XJ). It grounds out through the transmission housing, which is connected to the engine. So if the engine block ground is loose or corroded, the electrical path may be too small for the necessary power to get the starter to turn, while still leaving all your accessories functioning.

I learned all this at 3am after sobering up and discovering that I could listen to the radio and turn on any lights I wanted, but couldn't start the damn thing!

Thanks Wraithblade, Hopefully I can get out there in the morning to check it all out. We didn't cool down here until after it got too dark to work (we topped out at 109* locally!!). Your explaination makes quite a bit of sense. I'll update when I have some news.

Thanks,
Pat

Well, the grounds check out. I tightened them all down and still no cranking. Tomorrow morning I'll go out and check for power at the trigger and starter and go from there.

Pat

Go out and wack the side of the starter with a hammer and see what happens. When the brushes get worn, they sometimes don't seat all the way down and hang in the guides a bit. If your starter is coverd in oil (or has been covered in muddy water), it often seeps into the starter (don't know how or why but it does) and also causes the brushes not to make contact.
Number one on the list of things that make a starter screw up, is the brushes, worn or dirty.
The next most common, is no juice into (from the igniton switch) or out of the starter relay (starter relay full of rust or mud).
I'm not real sure about the MJ starter relay, but the XJ relays are marked. The spade connectors on the relay often have a "I" next to one spade connector, which likely means ignition (power in) and another marked with an "S" (starter) power out. The markings are sometimes different but not too hard to figure out. A simple test light may narrow it down for you some.
The wire from the starter relay to the starter solenoid has been know to get damaged, on the 87's it just kind of hangs there and has little protection.
The solenoid rarley fails, I've never seen a bad one. I once saw a solenoid piston that was rusted solid, but a little oil cured that.

Make sure there isn't any grey, pasty looking stuff between the battery and the clamp on the cable too! That is lead oxide in moisture suspension and it won't allow power through a lot of the time.

Well I have power to the soleniod, I back probed the trigger wire on the relay, I guess it's called (The thing next to the battery) and I got power through the lead when the key is turned to start. All the connections are tight and clean on the starter itself. I didn't check for power at the starter, due to the fact that my e-brake is non functional, and I really would rather not have the truck bisect me .

Looks like I'll be getting a new starter soon.

Thanks for the help.

Pat

Phager said:

Well I have power to the soleniod, I back probed the trigger wire on the relay, I guess it's called (The thing next to the battery) and I got power through the lead when the key is turned to start. All the connections are tight and clean on the starter itself. I didn't check for power at the starter, due to the fact that my e-brake is non functional, and I really would rather not have the truck bisect me .

Looks like I'll be getting a new starter soon.

Thanks for the help.

Pat

Click to expand...

Sounds like a starter. It'd be tough to not have power at the starter, the wire runs right from the battery's + terminal to the starter, and the starter grounds out to the block

Yeah, I noticed that too . I'll be buying new positive and negative cables while I'm at it, the PO had replaced the clamps and battery before I got it, but there is sure to be corrosion in the wires, and the negative cable running down to the block looks to have some slight cracking on the insulation, and I know it's gotta be worse in side the insulation.

It'll be a few weeks before I can get it done, since I'm between jobs a the moment. But I should be able to get the funds up in a couple of weeks.

Pat

I would do cables first, because I have had LOTS of them break inside! Put a block fore and aft of all 4 tires, put it in neutral and try cranking it straight off the starter! (because what are you going to do when you replace the starter and it STILL doesn't turn?) BTW, have you turned the motor by hand?

I was planning on replacing the cables first, since they are cheaper then a starter, just sort of mentally preparing myself for the $100 cost. I haven't tried turning the engine by hand, as I didn't see a reason to try. I haven't had any problems from an engine stand point in the couple of months I've owned it, and it was running just fine when I parked it last (My wifes taurus gets slightly better gas mileage so we use it primarily) so I don't think there is any issue with the engine being siezed or anything along those lines.

Pat

Time for an update,

I decided to go down to Napa and pick up a couple of negative cables (One for bat -> block, and one from bat -> rad support) along with a marine terminal to make connection/disconnection a bit easier. Got them hooked up and she starts! I really wasn't expecting it to start seeing as it has been sitting for 2 weeks and when this saga started I was barely at 12V, I figured I'd at least need a jump. I will say that this has really taught me a lesson, I was very doubtful that it was a grounding issue and I was completely wrong. For anyone who reads this who's having weird electrical issues make sure you check your grounds!

Here's a pic of the old cable:


I am by no means done, I still need to replace the valve cover -> firewall ground along with the positive cables. But this hopefully will be sufficent to get me by until I'm gainfully employed again.

Thanks for all the help guys!

Pat

PS I'll be sending out membership dues in oct (When financial aid comes in) at the latest. And if I can find a damn job it'll be before then. Between my DW problem and now this, I'd be remiss if I did anything else.

Thanks again!