91 Cherokee with 4.7 stroker. It has a cracked exhaust manifold.


Idles a little rough, drives OK until engine is warmed up good, once engine gets warm it acts like its running out of fuel. Then it stalls, and backfires when you hit the gas. You can just mat the pedal and make it where you've gotta go, but you're backfiring the whole time and it seems to have no power. If i pull over for 20 - 30 minutes it will run better for another 15 to 20 minutes then start acting up again. Will try to get issues to happen tonight and get video if I can.

Was told to check Map sensor. Before I spend 60 dollars on that do you all have any recommendations? TPS sensor? CPS sensorr?

 

MAP on a 91 is fed via a vacuum tube from the intake manifold to to the firewall. Make sure this is in perfect condition.

What mods have you done to the fuel system? Larger FPR and injectors?

But it is more than likely being caused by your cracked manifold throwing off the O2 sensor, which only matters once you enter closed loop after the engine warms up. Pretty typical really.

 

I bought it used, but the previous owner was in the air force so he kept pretty good records on the build. Here is what i can tell you about the build:

Intake from 99 4.0
Injectors are LS1 injectors

Fuel rail as far as i know is stock
Fuel pump as far as i know is stock
Fuel pressure Regulator is stock

 

CEL?

 

I had been getting 4 5 * i think that was the one *

for overdrive solenoid sensor

And i had been getting battery over voltage.


Neither one have come on in over a month though.

Not sure if it helps any, but brake booster and master cylinder replaced 2 weeks ago, Fuel filter replaced in August, New NGK plugs and BWD wires installed this weekend after the problems started happening again (had not done this since this summer).