Turns over, won't start...

[novawingnut]

'88 4.0L w/ 122k, ran great up until yesterday...cranks fine, but won't fire, no spark. Tested the coil and the ignition module, all good. Checked the voltage going into the coil - measuring 5 volts from the single yellow ignition wire and 10.8 volts from the yellow ignition output wire. Thoughts? :oops:

[project88mj]

i had the same problem

 

you might not be getting enough fuel pressure or any at all

 

after 3 days my dad and i pulled the gas tank and checked the fuel pump assemebly and there is a little section of rubber hose. the gas had eaten it away over the years

 

it also cloged up my fuel filter

 

check the filter first if its clean then i would go there :D

 

 

sorry i don't have pics anyone who has a fuel pump assembley picture

please post it with an arrow to that little rubber hose thatwould make this thread much better :oops: sorry i don't have one :oops:

[project88mj]

found one:

 

[Akula69]

Check the battery to engine ground - ensure it's tight and clean. It's located behind and slightly below the oil dipstick tube.

[Eagle]

The most common cause of sudden failures to start is the CPS (crank position sensor).

[Wildman]

:agree:

 

For a crank and no start, the CPS is almost always the first item to check :brows:

 

Here's the link for the check/replacement of the CPS (Near the bottom of the page)

 

The first "trick" is to unplug / replug the connector, and just might get it started.

 

Do the volt/ohms test first, and that will give you an idea where to go from there.

[BLHTAZ]

The most common cause of sudden failures to start is the CPS (crank position sensor).

X3 ... with a sudden no start / no spark, it is nearly always the CPS.

[novawingnut]

I was thinking about the CPS as the next step last night...my brother's '87 XJ did something similar symptom-wise a few years back and I think that ended up being the culprit but I honestly don't recall...but I know these ignition systems are notorious for that issue, just haven't had to fix the problem on any of my jeeps yet.

I can hear the fuel pump so I know it's kicking in, and the filter looks to have been replaced at some point along the way, so I was leaving the fuel pump/pick-up as a last resort to check...it's had very little mileage put on it over the last year or so, so the gremlins may be wreaking havoc from it having been sitting.

OK will check the CPS next....thanks guys~ ;)

[FxRacing282]

id turn it over and smell for un burnt fuel. if its there then X4 on the CPS

[ejndssn]

when in doubt check it out "CPS" :brows: X5

[novawingnut]

So I left a trickle charger on the battery overnight since it was getting worn down from swapping out coil, module, spark check, etc... Got all set up after work to check the CPS, but for kicks and giggles thought I'd try to start it before hand...AND THE DAMN THING STARTED RIGHT UP! :ack:

I realize this was likely a freak thing and I still need to check the CPS, but I needed to turn the damn thing around so I can start swapping the plow frame and components over, so at least I got that process started. Anyway, many thanks for the input from all...will continue with the diagnosis this weekend, fingers crossed it isn't going to be a ---> :wall:

[Wildman]

Maybe not a freak thing........just sitting, the CPS or the connector "dried" out. Still check the voltage / ohms on that sucker, and really plan on changing it out........before you have to lay in a foot of snow and drop the tranny to change the CPS :headpop:

 

Oh.......and have fun installing your undercarriage.......you have any questions......drop me a note ;)

 

The only real problem is getting that one bolt in behind the alternator, other wise......it's a straight bolt on.....with a couple 1/2" holes to drill :D

 

And if you had the OEM tow hooks on your MJ......it's even easier :brows:

[novawingnut]

Maybe not a freak thing........just sitting, the CPS or the connector "dried" out. Still check the voltage / ohms on that sucker, and really plan on changing it out........before you have to lay in a foot of snow and drop the tranny to change the CPS :headpop:

 

Oh.......and have fun installing your undercarriage.......you have any questions......drop me a note ;)

 

The only real problem is getting that one bolt in behind the alternator, other wise......it's a straight bolt on.....with a couple 1/2" holes to drill :D

 

And if you had the OEM tow hooks on your MJ......it's even easier :brows:

 

Luckily the CPS problem is on the XJ donor plow truck...NOT my MJ, altho I will be reselling the XJ shortly (bought plow with truck attached), so will do the CPS either way...maybe even do it on MJ as well just to be sure.

 

And no, not quite looking forward to the plow frame install but may just tow the XJ up to my brother's with my MJ, put it on his lift and swap it all over in the warmth of his garage (but if I do it @ home and get stuck you may well be hearing from me) :yes:

 

I may need a hand installing the air lift system as well (thankyouthankyou again), and he may likely do the same in his '87 XJ plow truck if the system works out on my MJ (I love being surrounded by engineers....never a shortage of help when I get stuck and start throwing tools) :thumbsup: