Have a 88 jeep Cherokee Laredo 4.0 i6 187,000 bought it used ran great had automatic transmission slipping issues. Had tranny replaced drove it out to my my dads spent a ton of money fixing it up for my son. Here's my issue ever since then it has never started and ran right. Here is what I have replaced and tried.thing runs rough, misses, and backfires. I am so frustrated I am ready to jerk the motor, wiring harness, and computer for a newer setup. Jeep does have a strong gas smell before first starting. Any help would be greatly appreciated.
List of stuff replaced and tried
New cps sensor old one got to close to the manifold
New tps
Cleaned throttle body
New temp sensor
New fuel filter
Cleaned fuel tank while I had it out
New fuel pump
New fuel pressure regulator
New plugs
New plug wires
New distributor
New distributor cap
New rotor bug
New coil
Used cruisers tips and Drilled oversize holes for the cps and it made it worse instead of better. Jeep was dying at stop signs and lights was hard to restart.
Checked all vacuum lines
Replaced egr valve
New O2 sensor
New water pump just because it seemed to be running hot.
Replaced thermostat
Cleaned all sensor plugs and injector connectors with electronic cleaner
Checked intake bolts a few where loose I tightened them down. Does not seem to have a leak around the intake
Replaced throttle body gasket old one trashed when cleaning throttle body real old.
Cut out the old firewall plug and reassembled per cruisers page made no difference
Ditched the catalytic converter
Replaced the muffler
Tested fuel pressure at the fuel rail before and after replacing regulator

Thank you,
Mark Pierce

 

Your post is a bit confusing, info is scattered. It ran fine before the trans replacement, did it still run fine after? At what point did it start running crappy? Did it start acting up immediately after replacing stuff? Smells of gas before starting, odd. Where's the smell strongest? You need to find that leak.

 

Only supposed to drill the upper hole on the CPS.

 

Sorry I just started listing stuff. When I bought it the transmission was bad I knew that. I had it replaced and it still ran fine. I pulled it into the shop and started some other stuff on it interior, lifted it, new rims and tires, painted it, so it sit for about 6 months. I occasionally started it just to keep everything moving and drove it around the pasture. After I did all of that and took it out on the highway that's when things started going south. The other stuff listed that I did was in an effort to correct its bad performance.i don't see a fuel leak anywhere I smell the gas the strongest after turning it off. Could that be bad injectors?

 

Cruiser only drill the top hole not the bottom one as well. I had read somewhere that both drilled out would give you a little advance. Is that not the case?

 

Drilling both could allow advance or retard, but not much I'd think.

Definitely start by finding the leak. With the engine cold turn the key on to make some pressure and start looking/sniffing. The pump only runs for a couple seconds with the engine off so you may want to cycle it every few minutes while hunting around to keep the pressure up. Injectors would be my first suspicion.

 

I think the advanced CPS has the sensor a bit off center on the bracket, maybe more like a few 1/8 ths, not thousandths.

Always good to rule out that Pesky MAP tube...They crumble easily sometimes>>

There is a brittle little tube. It comes out of a rubber plug, low on the engine side of the throttle body. It runs back to the firewall, then up to your MAP sensor sort of high up there near center on the firewall. CRUCIAL!! The MAP will tell the ECU to dump fuel with less/no vacuum. Any crack or blockage any you won't be happy It will be rich. (maybe black smoke, fouled black plugs). You can pull the line off the MAP and feel for vacuum with your finger. If it runs!

 

Thanks guys I will try the map sensor and the vacuum line then roll back to the cps sensor after trying to locate where the strong fuel smell is coming from. Could the map also be causing the injectors to dump too much fuel and that be in fact the strong smell?

 

Here's the advance mod:

Tip 7, second part.

 

what's your catalytic converter's status? I have an 89, and had similar issues as my cat started to die...

easy to check with a temp sensor.

 

Around thanks no cat removed sometime before I bought the rig.

Thanks cruiser I will check it out.

 

The MAP uses manifold vacuum to gauge how far you have your foot into the throttle. The more you open the throttle plate with your foot, the lower the vacuum goes. It does the basic, root fuel supply, the rest just "trims up" what the map is telling the ECU. It's never "ignored" and always a major player. The sensor it's self doesn't seem to fail often, but the vacuum line to it might blow to pieces if you try to add wiper fluid. With no vacuum to it it will tell the ECU you have the petal on the floor, and it's signal to the ECU will be "provide max fuel". It will work with manifold vacuum from anywhere. I like having mine there on the TB as designed.

Now to confuse things a bit...if YOU hold your petal on the floor, (presumably) it's your TPS that tells the ECU to cut off injector pulse entirely, because you are holding it floorboarded because you might be flooded.

If the gas smell is under the hood...we all should have a little fire extinguisher...Your stock injectors are known to leak and cause the Jeep to have "configuration" issues.

 

If the fuel smell is only with the engine running then possibly. Having no cat and a rich condition will be spewing raw fuel from the exhaust, but only the exhaust.

 

Ok I changed the map sensor today and the vacuum tube to it, started the jeep then gave it some gas and it stumbled, bumbled and backfired. Could I possibly have an intake leak causing a low vacuum situation throwing everything off? Not sure what to swap now all sensors are new. Not sure what else to try at this point. No strong fuel smell after running it for a good 15 minutes. Going to pull all of the new plugs and check them and recheck the plug wires.

 

Did you change the fuel pump just because you wanted to change it? Do you have stock fuel injectors (large body)? The stock injectors are notorious for leaking on the body where the plastic and metal meet. I would switch those out to the 4-hole style Volvo injectors (I did and never looked back). Did you do the TPS re-calibration procedure after you replaced it? I assume you have the plug wires on right??!! Wouldn't be the first time someone puts it back on #2 instead of #1. How about the transmission mount-did you change that? Is the transmission cocked or not snugged up tight?