cherokee headache please help

[Ecomike]

Must be in the air. My 93' is having about the same problem. I havent tried WOT yet but i will. Sounds like it might be the ballast resistor. Can i bypass that by just eliminating it?

The ballast resistor slows the pump down except at start up the first few seconds, makes it quieter, and extends the pump life, but several people have bypassed theirs. Not a problem to temporarily bypass it. They are real inexpensive and easy to replace!

 

[willy51]

Ok, i will bypass it before i leave the office an see if it makes a differance. I allready replaced the pump. I'm having a problem with the fuel draining back to the tank on a long sit (over night +) iv heard of some people putting check valves in the line. Any wisdome here?

 

[cmichaud84]

ok well i check for injector pulse, have it. checked for spark with inline spark tester, have spark. it wants to start when i first start then it seems like it is flooding, so i give it wot and it tries to start again but nothing. like one of the post before i think im getting fuel bleeding back to the tank when it sits. so if i hook up a fuel pressure tester i should have what pressure at the rail? and also where is this resistor so i can try jumping it. or replacing it

 

[cygnus58]

Could you have momentary, no load, fuel pressure at the Schrader with a clogged filter?
edit - as EcoMike said - "All the Time".
It's usually mentioned early on in posts, (the fuel filter) but I don't
think I saw it yet.

 

[cmichaud84]

yes i replaced w/ pump

 

[cmichaud84]

i haven't tested the fuel pressure yet with a gauge but i will tiomorrow it should be around 31psi right?

 

[cmichaud84]

so where is this ballast resistor and how do i replace it? do i replace the relay also?

 

[Ecomike]

You are going to need to search here in older threads for some of your questions. For instance the Ballast resistor is already posted with pictures in older threads here. It is a white ceramic, rectangular block about 1", 1/2", 4" ong, on the drives side fender wall up front, if your year model has it. Not all years had it.

I think your year used the same fuel pressure regulator mine did, it is on the fuel rail at the begining (or end) of the fuel injector rail. It is spring loaded with a vacuum control. Pressure is 31 psi at idle with the vacuum line attached and 39 psi with the vacuum line disconnected.

Leaking fuel injectors, or.....?

I just reread this entire thread and it now sounds like a problem I once had with cold engine start up. Once I coaxed the engine to start (only worked in the afternoon on hot days, not on cold days, on cold days it never started), it restarted all day just fine. Turned out the MAT, or IAT, air intake manifold temperature sensor was giving bad cold engine data to the ECU, and throwing off the open loop cold start Air to fuel mix calculations in the ECU, so it never could fire up, too lean to start in spite of adequite fuel pressure.

Dust off your DVM or ohm meter, and test the MAT and coolant temperature sensor to if they are reading the correct resistance for you current ambient temperature. the test values are posted in dozens of threads around here, but make sure you use the right year, sensor data. I think the CTS changed and moved to the thermostat housing in 1991. The MAT may have stayed the same from 87 to 95, not sure. Yours is a 93, right?

Anybody got 93 CTS and MAT resistance versus temperature spec data handy?

 

[cmichaud84]

yes it is a 93 and a testing procedure would be nice if someone has one

 

[cmichaud84]

the ballast resistor now that you have told me where it is was extremely hot now that i think of it before this whole no start condition. when running is this resistor supposed to be hot? does anyone know the ohm reading on this part is please.

 

[cmichaud84]

i checked the MAT and CTS and the CTS is reading 11.57 MOhms and the MAT is reading 11.37 MOhms my ballast resistor is reading 1.8 MOhms what can you tell me from this

 

[cmichaud84]

also i just checked my fuel pressure and it is at around 36 psi when i just turn the key, and at start up it is at 40 psi the whole time. what is going wrong here

 

[cmichaud84]

oh yeah the motor was cold at 75 degrees

 

[Ecomike]

the ballast resistor now that you have told me where it is was extremely hot now that i think of it before this whole no start condition. when running is this resistor supposed to be hot? does anyone know the ohm reading on this part is please.

PM you email address. I found a ballast resistor bypass relay listed on a pdf I have.

"Ballast Resistor (Cherokee)
A ballast resistor, located between fuel pump relay and the
fuel pump, is used to reduce voltage to the fuel pump. This reduces
fuel pump noise during operation. Ballast resistor is mounted on
fender panel, next to washer fluid reservoir.
When fuel pump relay is energized, voltage is supplied to
fuel pump through the ballast resistor. During start and wide open
throttle conditions, ballast resistor is by-passed and fuel pump
receives its voltage from ballast resistor by-pass relay.
NOTE: Wrangler DOES NOT use a ballast resistor or ballast resistor
by-pass relay in the fuel pump circuit. The PCM operates
fuel pump through the fuel pump relay during all operating
conditions.
Ballast Resistor By-Pass Relay (Cherokee)
A ballast resistor by-pass relay is located on a bracket next
to power distribution center (next to coolant recovery bottle). By
switching the ground circuit on or off, the PCM can control fuel pump
(power) feed. The ballast resistor by-pass relay receives its voltage
from fuel pump relay.
Normally, voltage is supplied to fuel pump through a ballast
resistor. At wide open throttle, fuel pump receives voltage through
the ballast resistor by-pass relay, which speeds up fuel pump to
compensate for higher fuel demand."

 

[Ecomike]

i checked the MAT and CTS and the CTS is reading 11.57 MOhms and the MAT is reading 11.37 MOhms my ballast resistor is reading 1.8 MOhms what can you tell me from this

OK, you are throwing me with Mohms, if that stands for MegOhms, then something is seriously wrong, like you have the probes in the wrong holes on the meter, or something even wierder or all three of those are toast, which I doubt.

Fuel pressure looks good. It will not drop until the engine is running and holding vacuum.

MAT and CTS should be at about 9,000 to 11,000 ohms, or 9Kohms to 11 Kohms at 75 F.

 

[cmichaud84]

ok just checked CTS it is 12.56kohms and the MAT is 12.62kohms and the temp was around 70 degree. thank you guys cause i really need this thing back on the road. so what next?