I've got a very frustrating problem here. Customer brought in a 1990 Jeep cherokee limited, 4whldrv, automatic. We replaced the engine with one from a 1996. All the appropriate electronics were switched from the old engine to the new including, distributor, cap, rotor, coil, CPS, flywheel, intake and exhaust, all injectors (already on old intake). The problem is we now have a no start/no spark condition. This swamp is common at our shop, (newer 4.0L into older jeep) and always goes off without a hitch. This is the first time I've run into this. We've replaced the CPS, coil and ignition module check out O.K., Distributor checks out. We even put all the suspect parts into another jeep and they worked fine. The computer has also been replaced but to no avail. Any input would be appreciated. Thanks. Jesse
No we don't. We used ALL of the electronics from the Bendix system. There are absolutely NO 1996 electronics on this engine now. This is a swap we've done multiple times and never had this problem. As long as all the electronics are swapped over from the old engine it works fine. This problem is not because of incorrect electronics.
My 88 has a ballast resistor on the fuel pump. I was told if this doesn't work, the computer won't send a spark. Maybe the connection got knocked?
The resistor is out on the driver's side fender on ours and is a ceramic rectangle type.
Does the distributor have a ground? I have seen rust interfere with a distributor signal.
There might be one other computer control ground on the inside firewall just above the gas pedal. I am not sure what that one runs, but the engine won't go without it. The YJ's ground the fuel pump in that area, don't know about the Cherokee.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06
formatting link
(More Off Road album links at bottom of the view page)
I would be looking at the starter relay for a punky connection next I think. If it isn't sending enough voltage on starter bypass to the pump, maybe the coil also isn't getting enough.
The green wires I think are the ones to clean.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
K....injectors aren't firing. Can manually operate relay to activate pump but when cranking the injectors won't pulse or let fuel through. Sounds like CPS again, doesn't it? Mike, in regard to not enough voltage at coil....there is 10 - 11 volts.
Just a thought>>>>>>>>> Since you dropped in a newer engine, is it possible you clipped a harness wire, that is is shorting itself out at the firewall?
I had a new engine dropped into my Cherokee, it gave the same symptoms you describe, and we finally found a frayed harness wire that kept shorting out against the metal.
There is a CPS or pickup module and ignition module inside the distributor as well. The distributor got clocked in correct right? That shouldn't interfere with the power though, just the timing. Hmm, but the engine needs both CPS signals to fire up, if they are not in sequence??...
Anyhow, the distributor should be clocked with #1 plug wire as far away from the block as it can be or in the 6:00 position looking at it from the side of the engine. The base only fits one way so it can bolt down. It must be bolted in to make the ground path.
You are not getting any power to the fuel pump or ignition when cranking correct?
They do use a modified ford starter system with a starter relay that has a power bypass used during cranking. There are a couple green wires on it. I have seen these wires get mixed up on several different engine removal or burned harness jobs. If you have 10 volts at the coil during 'cranking', then this shouldn't be the issue.
I live in the rust belt, so grounds are normally the first thing I go after. I use a booster cable from the battery negative to the engine, then the distributor shaft, then the body just to verify the major players are there.
I have also seen bad alternators suck the ignition down. I would be tempted to unplug it just for the heck of it and try. Depending on the alternator, the field wire tags the coil power.
Then just to toss a strange one in, if the battery has a bad cell, it can still give enough power to crank, but the electronics won't turn on. This is worse on the newer Chrysler made systems than the old ones though.
I doubt it has any bearing at all, but the O2 sensors are bad. All the Renix O2 sensors are under recall. That shouldn't affect the start though...
A bad connection on the Throttle Position Sensor can affect starting too.
There are a few more guesses for you.
It's likely something silly. I would appreciate the follow up.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
I too suspected the throttle position sensor as of last night but have yet to test it. The distributor is indexed correctly and has been swamped into a jeep that runs and it works great. There are no "clipped" wires as we tore apart the harness and checked thoroughly. The O2 sensor is good (fairly new) but as you said, would not have bearing on the no start condition. As far as the distributor goes, you mentioned that it should be clocked 6:00 position. I believe it's about 5:00. I've seen these engines not fire when the distributor was only .020" out. But as I said, the distributor is indexed correctly. Anyway, I'll check the TPS and the starter bypass. The wires were never unplugged from the bypass so I don't think they're mixed up but it could be a bad solenoid. I'll report back this afternoon and let you know. Thanks for your input Jesse
Ok, you have a MAP up on the center firewall that sends a signal to the ICM under the coil, the CPS and distributor pickup, the throttle body IAC and TPS....
How many ground wires do you have bolted to the dipstick mount bolt? Mine have 4 with 2 eye loops. I have an 87 and an 88.
You are right about the real distributor clocking being closer to 5:00, I looked. Book is different...
Does the fuel pump cycle on when the key first hits run? It's ground might be on the inside firewall above the gas pedal. Something critical grounds there anyway.
Something sounds like it is going on related to that circuit because of the effect when you jumped the ballast resistor. The orange wire with the stripe is the one linking the systems I think. I have seen one of those pinched and have seen and heard of several melted enough to short the system down, down behind the engine where the exhaust crosses over. There is a sensor on the T-case or something down there.
Could you have blown a fuse link? They are coming off the solenoid/relay at the same terminal as the battery cable.
GREAT NEWS!!!!!!!!! Problem solved. You're not going to believe it but it all comes down to wiring. (which I suspected in the first place but thought I had eliminated that). I went back into the harness and started checking wiring. I realized that when I was checking the ground wires inside the wire loom that I missed about a 18 in section just after the main splice on the firewall, engine side. They looked good but decided to investigate further. Upon a more thorough visual inspection I noticed two little pin holes where someone had apparantly probed the wires at one point in time. Remembering that the customer had told me he had submersed the jeep past the windsheild in soupy water at one time I decided to remove the covering on the wires.......They literally fell apart.
So....it all comes down to a bad ground. It was something simple but hidden. Thanks again Mike for all your input, I work on these jeeps on a daily basis and I've never had one baffle me in 10 years as much as this one has. Thanks
Man, those damn grounds on the old Jeeps are bad enough without intentional damage. If I have to probe a wire, I put a spot of RTV into the hole to seal it or at least some dielectric grease. (after seeing exactly the same thing you have found)
If that Jeep was playing in the puddles, you might want to check the tranny fluid out for water. Jeep didn't put a high water vent on the tranny like they did for the diffs and t-case.
Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.