I have a 95 XJ that intermittently will not start. If I wait a bit or try enough times it eventually does start, but sometimes can go days without a successful start, and then a week or more with no issue. If I ever do get it started it never stalls, I can drive it for hours without issue.

I have had two mechanics look at it. Both times it had not started for multiple days and was prepared to tow it but then it started and was able to drive it to the shop(s). First mechanic had it for 2 days and it started every time under all conditions and he checked the distributor, spark-plugs and starter etc. all of which looked good and are all quite new. The fuel rail for the injectors definitely has pressure(though I don't have an actual reading there). He did not pull the fuel pump and inspect.

The second mechanic actually got it to not start and the computer told him bad cam sensor. He replaced that and it seemed fine, but he was not convinced for sure it had resolved the issue, but since it was running again I took the car back.

Its been a week since then and the no starts are getting more frequent. Im wondering if it might be some electrical or ground issue or if its possibly the computer itself that is going bad? There are no completely obvious bad wiring, but I need to look closer. I was wondering if anybody here had any thoughts or suggestions?

 

Please clarify, is it no start as in you turn the key and nothing, or does it crank but won't fire up?

Either way, you need to definitely go through the grounds and battery cables - make sure they are clean and tight. Don't just look at them, take them off, scrub them up with some sandpaper/wire brush until they're bright and shiny and reconnect them securely. Don't forget the 2 in the cargo area, drivers side, behind the trim panels. The fuel pump grounds there.
While you're at it, inspect the wiring everywhere where you can see it and repair anything that's not sound. Definitely examine the small vacuum tube that connect the intake to the fuel pressure regulator (this is on the rail) - I just had to replace that tube since it cracked on one of the bends.

After that (assuming you're getting a crank-no-start), you need to get a fuel pressure gauge. Either buy one (~$20 at Harbor Freight) or borrow one (free as a loaner tool from your local parts retailer) and check the fuel pressure WHEN IT'S HAPPENING. Fuel pumps are flakey when they fail, they'll run OK for a bit, then get wonky, then run OK. Checking the pressure when they're OK tells you nothing, checking when it's wonky will expose a bad pump.

Keep us posted!

 

when I turn the key it cranks but it will not fire. The started sounds strong and it was recently replaced. occasionally it starts to turn over but can't get all the way there.

thanks for the checklist of things to look at, will take a look and see how it goes.

 

Specifically, what code did he get?

 

I don't have the specific code the mechanic got, but im going to have access to a reader tomorrow and will see what codes its giving now. will add that once I have details.

 

Test your Crank Position Sensor, and your Cam Position Sensor (it's in the distributor).

 

Next time it won't start, see if the headlights work. Then try shifting to Neutral and trying it. NSS

 

I have been out of town most of past 2 weeks so am only now getting back to looking at it.

when I tried it this morning it started multiple times in a row. I had a fuel pressure guage on the fuel rail and it read consistently between 30-40 psi. this is in the on key position or when it was running.

I checked all 6 grounds under the hood and all seemed to be good. I checked them both by resistance and by voltage.

The only codes I can get are the ones from the check engine light. which gave me 12 and 13( its OBD-I so the scanner I borrowed could not read it even with the adapter I have for the computer). I looked at the MAP sensor and noticed that the vacuum line was not even connected to the manifold so I fixed that. and the next time I stated it up it sounded better. I then disconnected the MAP vacuum line again to see what happened and it sounded a bit rougher. I reconnected it and tried to start it again and finally reproduced the no start for today.

one question I have, is what should I expect if a MAP sensor vacuum line is not even hooked up at all?

it seems like it has a better chance of starting if the engine and the outside temp is colder. but as either the engine or the day warm up it gets worse. can't totally confirm that.

I did not check the crank sensor as I am not totally sure how to get at that currently.


at this point im getting it towed to a recommended mechanic on monday to see if they can make sense of it. Hoping they can produce the no start and really see what it is. I feel like its got to be something electrical, possibly the computer itself? not really sure how to test it further with my limited means and without just taking the whole thing apart.

any other thoughts would be welcome though.

 

what would shifting it to neutral do differently or tell me?

 

MAP signal voltage will remain at 5.0 volts or so.

 

If it starts consistently when you shift it to nuetral after your no start symptom this would indicate the neutral safety switch (NSS) could need cleaning/replacing. Otherwise look into the crank position sensor (CPS). I believe your symptoms point more directly at this being the issue. Oh, and don’t just test the grounds, remove and clean them. It’s a good maintenance practice.

Good luck!

 

If it won't crank/spin at all then the NSS may be dirty. In your case, it's spinning but not firing which is often a failing crank or cam position sensor. A failing crank sensor may not set a code.

 

I do not believe if it has been determined that it is really "not firing" during these episodes. However, you do have that 13 code. Reset the codes and see if that code reappears, and/or test the MAP sensor.

And see if you have spark (or not) during a no-start.