93XJGreenMonster

The following is my original post and then additional info follows. I can't figure this out guys, please help.

My 1990 Cherokee won't start. Started out it would not start unless I disco'd the CPS and plugged it back in (sometimes it would work, sometimes not). It also idled very low, in the 300s. To keep it from stalling at stops I would put it in park where it would move up to the 500 range. Sometimes then it would stall. I decided to get underneath it while it idled and I could hear the fuel pump sputter when the idle would dive. So I coming back from the parts store with the new pump it dies and wont start at all. Get it towed to the house and I install the pump. Still doesn't start. When I did the pump I also did the filter. Anyway, I decide the CPS probably had to be replaced too so I did that. Still doesn't start. I've checked vacuum lines, checked all connectors for corrosion and poor connections. I can't figure it out. I've looked around the forum and I can't find any other ideas to try.

Prior to it dying completely I cleaned the throttle body and replaced the air filter to try to get the RPMS up, which seemed to help for about an hour. I also sprayed a little throttle body cleaner in the injector holes. (Which, sorta off topic but maybe not, I noticed that on injectors 1-3 there was no change in performance when i squirted the cleaner into the holes, whereas 4-6 it would nearly kill the engine like spraying into the throttle body. I suspect that the orings on 4-6 are going out but no fuel is spilling out. Further, I noticed that the injectors on 5 and 6 appear to be te originals and 1-4 have a different model in them.)

Summary:
New fuel pump
New fuel filter
New CPS
New Idle Air Controller
Tuned the TPS
Checked all vacuum and electrical connections
Cleaned the throttle body
Replaced Air Filter

93XJGreenMonster

^Bump^

Any ideas at all anyone?

Throttle Jockey

could be a coil or cam sensor. another thought check the grounds form the battery to the engine and to the body. mine did this same thing and it turned out to be the ground strap from the engine to the body, the fuel pump wont work unless it's there.

93XJGreenMonster

I can hear the pump prime and I'm getting pressure to the fuel rail, so I think I'm good there. I'll see if I can do some diagnostics on those sensors but I'm not too enthusiastic.

Anyone else weigh in?

88chief

X2 on Checking coil and cam sensor. I know you said you replaced the crank sensor but I would check it again and make sure you did not get a bad one.

93XJGreenMonster

The cam sensor is going to be in the distributor right? And if I read enough, the relationship to the crank sensor tells the computer where everythings at so it stays in time right? Is the cam sensor replacable itself or do i need a whole nother distributor?

93XJGreenMonster

I remembered I had an inline test light for the coil and distributor. I put it in line from the coil to the distrib and it pulsed when I cranked it. I then went from the distrib to plug 3 (because getting to 1 and 2 are a pain in the *** with the radiator hoses right now) and it pulsed as well. I think that rules the coil out, but does it rule out the cam sensor as well?

What if what is happening is basically what happened to my 93 as well? On the 93 the cam gear got worn down because the distributor gear was rubbing and eventually got so worn that it wouldn't keep time. I didn't want to do a top end rebuild on it because I knew I'd end up doing the wole damn thing and I didn't want to get into it.

Just thinking out loud, if it's not the cam sensor, could it be that I need to get the crank to TDC and then re drop the distributor? Seems to me it shouldn't skip unless the distro gear or cam gear is worn. Hoping like hell the cam gear isn't warn.

And how about just pulling a distrib from a jy with the cam sensor in it?

93XJGreenMonster

I'm stumped. I've replaced the following:
Fuel Pump
Fuel Filter
Crank Position Sensor
Cam Position Sensor
Distributor and gear
Idle Air Controller
Calibrated the TPS
Checked for Vacuum leaks
Checked for electrical issues

I made sure the engine was in time with the distributor, moving the harmonic balancer to 0 on the timing marks and setting the distributor appropriately.

I can hear the pump prime, I have spark from the coil to the distrib, and spark from the distrib to the plugs.

I have pressure in the fuel rail.

WTF?!

Could the injectors not be spitting? Is there a relay/fuse for them?

What else could it be, this is driving me crazy!

Throttle Jockey

that is about the only explaination i can come up with. i think the injectors are controlled by the ECM based on info from the cam and crank sensors. you have fuel pressure in the rail and you are getting spark. any way you get ahold of a loaner ecm?

Jeepman659

Are you sure your PCM is still good? i mean other then internal problems you don't have alot left to really fix besides change spark plugs wires igniton coil if it's turning over you know your solenoid and starter are fine. so either something in the engine is f ed or somethings not telling the engine what to do.

93XJGreenMonster

I just pulled back the sheath on all the injectors to see if they're all wired correctly and found that number 3's wires have no insulation at all and are touching. I suppose that could have shorted the ECM/PCM (ECM/PCM are the same thing right?)

Can't see borrowing one, but I can probably grab one out of the JY. Should be under the dash to the drivers right, right?

I'l double check that the distributor is still in time, maybe the cam gear is worn. When I had it happen on the 93 though it cranked like **** whereas this is cranking like usual, normal sound and all. So yeah the starter and solenoid are fine.

Throttle Jockey

yes they are the same. you may be able to correct it temporarily to see if that is the problem. the pcm/ecm is typically pretty rugged and takes alot to hurt one. make sure the wires on the injectors are not touching with tape or something. disconnect the battery for a minute and see if it resets.

93XJGreenMonster

Just did, same result, cranks great no start though.

I think I'll pull the rail off tomorrow with the injectors attached to see if theyre spitting. Maybe hit them with some throttle body cleaner while theyre out.

I think I read somewhere all the things that the ECM has to have in order for it to start.

Maybe go through all of the grounds. I think Frank put something on here where all the grounds are. Seem to remember a couple on the tranny dipstick or something. The whole engine compartment is filthy with oil because I had someone do an oil change once instead of me and they left the dip stick not secured. Blew oil every friggin place as I was driving down the road. Maybe the filth has screwed up some connections.

Tonyffyl

Im having just about the same problem. Awesome cranking, plenty of spark, fuel pump works, correct pressure....but it seems like the injectors wont work. When mine runs, it runs pretty good. When it comes time to start it up again (not all the time) it will just crank....Im thinking ECM or maybe a bad ground

kbad

check your fuel tank....if it is original, then it may be your culprit.... look here.... https://www.cherokeeforum.com/f2/rep...e-4-0-a-50552/ ....then make sure your electrical is solid (i.e. strong/new battery, good grounds, no shorts, etc.)... good luck!