Intermittent (sp?) starting problem.

hjeepxj · Dec 1, 2009

My Jeep had been sitting for about 2 years or so and I started ressurecting it, it had a starter put in it about a year before I parked it, a new alternator about 2 years prior. I tuned it up probably, IDK, 30k miles ago (wires, plugs, cap, rotor) and I have a new battery (6 months - tops) over the previous three years before parking it, I replaced the TPS, the IAC sensor, and the CPS sensor.

About every fifth time I try to start it, it will crank untill no end but not fire.

The first time it happened, I immediately thought it was the fuel pump but I discovered I could always here it turn on when the key was on, and there was always fuel at the fuel rail.

Anybody have any advice? I drove it to work and am stranded untill it decides to fire...pretty awesome. LOL

cruiser54 · Dec 1, 2009

CPS, or Crank Position Sensor is probably bad or going out.

joe_peters · Dec 1, 2009

Well, you could have a number of issues.

Crap gas could be one. Unless you Stabil or something similar in the fuel SYSTEM before letting it sit, then much of the fuel system has varnish in it. If you did not drain the fuel and put all fresh in then the fuel may be weak, if you just added fresh fuel then it would just be diluted.

Grab some ether spray start and shoot it into the intake while someone cranks it over for you.

That is, if you even have spark. Have you checked for spark?

One big problem with modern (XJs are modern?) is that the battery can provide enough amperage and voltage for the starter to crank the engine fairly well, but during cranking the voltage can drop to below 9 volts, and you won't get an electronic ignition to fire if the voltage gets too low.

hjeepxj · Dec 1, 2009

cruiser54 said:
CPS, or Crank Position Sensor is probably bad or going out.

My experience (twice now) with the CPS is it either works or it doesn't.

hjeepxj · Dec 1, 2009

joe_peters said:
Well, you could have a number of issues.

Crap gas could be one. Unless you Stabil or something similar in the fuel SYSTEM before letting it sit, then much of the fuel system has varnish in it. If you did not drain the fuel and put all fresh in then the fuel may be weak, if you just added fresh fuel then it would just be diluted.

Grab some ether spray start and shoot it into the intake while someone cranks it over for you.

That is, if you even have spark. Have you checked for spark?

One big problem with modern (XJs are modern?) is that the battery can provide enough amperage and voltage for the starter to crank the engine fairly well, but during cranking the voltage can drop to below 9 volts, and you won't get an electronic ignition to fire if the voltage gets too low.

Fuel shouldn't be the issue, I've ran a couple of tanks through it over the course of the last six months.

I don't have anybody here to help me with checking for spark, so that's out right now. Is it possible the rotor in the distributor is on it's way out?

If it's not the rotor, I'm thinking about what you said - it must be between the starter and the distributor....coil?

I feel like an idiot here, most every issue I've had with cars has been straight foward, it works or it doesn't or it's obvious (starter going out for instance) but this is just a wierd one for me.

Johnnie Walker · Dec 1, 2009

hjeepxj said:
My experience (twice now) with the CPS is it either works or it doesn't.

Well, definitely check resistance @ the CKP (crank pos. sensor). In the few times that my XJ cranks/no starts, unplugging the CKP and plugging it back in makes it start right up. I know this means it should be replaced, but at least I know where the problem lies.

cruiser54 · Dec 1, 2009

My experience of 12 years as a service manager of a Jeep dealership from 1980 to 1992, and evolving with the XJs tells me that CPS on the Renix can definitely be intermittent. They sometimes don't make quite enough AC voltage to trigger the ECU.They even had a CPS bypass procedure to ensure all the voltage got through the harness to the ECU on the 87 to 89? models. If you have that big black connector on the driver side firewall, open it and clean the black tar out of it and the terminals. Also ensure the grounds are CLEAN and tight at the dipstick tube. While you're at the drivers firewall, remove the 15mm bolt holding the ground strap, scrape the paint off from under it, clean the eyelet and reinstall.

hjeepxj · Dec 2, 2009

cruiser54 said:
My experience of 12 years as a service manager of a Jeep dealership from 1980 to 1992, and evolving with the XJs tells me that CPS on the Renix can definitely be intermittent. They sometimes don't make quite enough AC voltage to trigger the ECU.They even had a CPS bypass procedure to ensure all the voltage got through the harness to the ECU on the 87 to 89? models. If you have that big black connector on the driver side firewall, open it and clean the black tar out of it and the terminals. Also ensure the grounds are CLEAN and tight at the dipstick tube. While you're at the drivers firewall, remove the 15mm bolt holding the ground strap, scrape the paint off from under it, clean the eyelet and reinstall.

Good advice, I think I'm going to clean everything you said, replace the CPS and cross my fingers that that works...

Gracias guys.

Intermittent (sp?) starting problem.

hjeepxj

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cruiser54

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joe_peters

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hjeepxj

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hjeepxj

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Johnnie Walker

Piece of Fish!

cruiser54

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hjeepxj

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