1991cherokee

Well I got the 91 xj with a new motor and rebuilt tranny... the motor turns over and wants to fire but will not start... everything is new on the motor. All sensors starter , alternator , firing order is correct , timing is set correct... only thing I have not changed is the ECU. So could it be the ECU or maybe something else ...

When the motor is turned over it pops through the exhaust like its firing correct but it just doesn't fire enuff to run... don't know if that makes anything clear to you guys but I've been f*ckn with this xj for the past 2 months and I can't get it running... so if anyone has a good idea or some possitive feedback it would be welcome

Norsk62

if it's just popping but not starting sounds like the distributor is out of position. Put the engine at TDC, pull the cap and verify the position of the rotor. If its where it should be it will be almost pointing to No1 spark plug wire. Notice I said almost. It will not line up perfectly and will be slight after No1. The CPS & CKP signals electronically ajust the timing through the ECU. One tooth off on the distrubutor translates to 30 deg of timing.

If this looks good. Check the firing order. Even if you think the wires are in the right order. Check them again. Also check to see that they are completely seated onto the cap. Try this first. Then if you ruled out the ignition, then check your fuel system to be sure you are getting the correct fuel pressure at the rail. Low fuel pressure will make the engine pop but not start. Pre 96 engines should have 42 psig at the rail peak, then bleed off to 35 psig. 96 and newer enginers are 50 psig peak, 45 psig while running.

Hope this helps

1991cherokee

Thank you for the help ... and I am taking it you mean after no.1 going clockwise ... I will be trying this tomorrow for sure , I know it is sitting on the mark dead on so ill index it again... thanks again

DFlintstone

You do have #1 at 5:00? (viewed from the side)

This link is for the HO distributor.

http://www.angelfire.com/my/fan/dist_index.html

1991cherokee

Sure do bud.. the distributor only mounts one way on the motor.

DFlintstone

Just wanted to be sure you had #1 there where I set the yellow connector since all the diagrams I've seen seem to be wrong.

Screwing around the other day I tried starting my (90 renix) with the MAP un-plugged. Just sputtered and rolled a bit, didn't start. I didn't keep at it.


Of course if you have it indexed right and you have spark and compression, gotta wonder if it's getting too much or too little fuel. Will it fire with starting fluid? / Or, are the plugs wet? Is your air cleaner full of acorns (like mine?)
If you push the deal on the fuel pressure testing port does it spurt fuel?

WHEN YOU INDEX THE DIZY THE ROTOR SHOULD BE A LITTLE PAST THE TERMINAL

seaguy

Was the replacement engine grounded to the firewall?

1991cherokee

To the best of my knowledge I had good spark , 41 psi fuel , all injectors are working , plugs are wet and I smell gas , I just did the whole process today with the timing over again and now I got nothing , not even a spudder.... if my ecu was bad would I get fuel and spark , or if it goes bad nothing works? I've checked grounds , only ones I see are from firewall to manifold , battery to inner fender/and block , and the grounds from the ecu .... they are all good , I ohmed the connections and there continuity. I'm just about lost on this ... I've had two people who are supposed to be good at this ***** look at it and neither can get it , and nor can I ..... what y'all think?

Norsk62

From what you are describing, I would replace the crank position sensor in the distributor. This sensor sends a signal to the ECU that fires the coil. You can either buy a new sonsor from the dealership or buy a new distributor which comes with everything, but a lot of the distributors from Autozone or O'Riely's are from Chineese manufactures, cost around $75 and have cheap sensors in them that tend to burn out pretty fast. I had one go out in two day only to buy a new sensor from the dealership for $110. Do your self a favor and just buy the sensor from the dealer and rebuild your old distributor. It's easy to do.

541_halseth

Even if it is the crank position sensor, its not located in the distributer the camshaft position sensor is. But rather on the driver side of the engine on the very top on the transmission and bellhousing. Here is the easiest way to change it. http://www.cherokeetech.com/VBull/sh...S-the-easy-way.

also check to make sure its connected, sometimes its forgotten.

DFlintstone

If the vac line to the MAP, (up there on the firewall) to the rubber plug in the throttle body, has even the slightest leak, it will flood.

541_halseth

Another thing no one has said and maybe unlikely but your ASD relay may have gone ****. it controls both spark and injection and not fuel pressure. You can have fuel but no injection when this goes bad

Cherockee

When you say "new motor", what's new about it. If it has an aftermarket cam you will need to install the distributor correctly, with a 3/16" pin to line up the distributor housing with the cam sensor. You may not be able to mount it to the block like it use to because aftermarket cams do not index the distributor drive gear correctly. Some people grind off the tang to mount it, or you could flip the dizzy around to the tang is on the opposite side. Just need to make sure your firing order is correct from there, the rotor will be just past #1 sprak plug wire with the engine at TDC on compression stroke.

r.center

My problems sounds almost identical. Please let me know when you find a solution.

cruiser54

Try this:

http://www.angelfire.com/my/fan/dist_index.html

I'll bet the dizzy is off a tooth or more.