XJ Bogs with Throttle Wide Open

[CpnJack]

Thanks. I looked up EGR and I think they stopped using them in 1990. The link is cool though with all of the test info in one place and straight to the point. Wish I had that a couple weeks ago. Jeep is actually at the mechanic now. I'll post up when/if they figure it out. Just hope the hole I put in the exhaust doesn't get in the way of them diagnosing the problem.

 

[kastein]

Yep. Egr is a RENIX only thing, not used on 91 and newer 4.0s/2.5s - goes for the xj/mj/yj, not sure about the sj which had some wonky air injection system.

 

[AtomicPunk]

Any results yet?

 

[joe_peters]

For CpnJack--test the oxygen heater relay.

 

[Shorty]

For CpnJack--test the oxygen heater relay.

I would think it would present more of a problem during engine warm-up if the O2 heater wasn't getting power. The O2 only needs to be about 650*F to function and 3000 rpm from a warmed -up engine should meet that criteria.

 

[joe_peters]

I would think it would present more of a problem during engine warm-up if the O2 heater wasn't getting power. The O2 only needs to be about 650*F to function and 3000 rpm from a warmed -up engine should meet that criteria.

I don't have a 94 FSM, so somebody that does can check the fuel section. On the Renix the power to the fuel pump is delivered in different ways, under different sets of circumstances. Key ON, power is from the B Latch relay and bypasses the ballast resistor, full 12 volts to the pump--lasts for 3-second until the ECU cuts the ground to the relay. The ASD relay does this in the later XJs also. Key to START, power to the fuel pump is through the starter relay, bypasses the ballast resistor, full 12 volts to the pump. Engine running, from idle to just short of WOT, power is from the fuel pump relay, through the ballast resistor where it is reduced to 6 volts. The ballast resistor was eliminated 94+. AT WOT--power to the fuel pump is from the oxygen heater relay. Now, as I said I don't have the 94 FSM but somebody does and can check. OP's problem is at WOT--is the fuel pump getting any power?

And that is why I suggested checking the heater relay.

 

[kastein]

Obd-I systems are completely different from RENIX... Afaik the o2 sensor heater is driven from the ecu directly and isn't controlled by 255247 different relays anymore.

 

[joe_peters]

Obd-I systems are completely different from RENIX... Afaik the o2 sensor heater is driven from the ecu directly and isn't controlled by 255247 different relays anymore.

So, OBD I and up no oxygen heater relay.

Thanks.

 

[CpnJack]

Hey Everybody. Since last post jeep has been to the stealership where they worked on it for 4 days and called me to give up. Fortunately, they didn't try to charge me, they were actually pretty cool about it despite not being able to figure it out.

Threw a few more parts at it included O2 sensor, CPS, IAC, Idle control (because I found one at the JY cheap), cap/rotor. Good news is I have a bunch of new or new-to-me parts and some spares now. Bad news, none of those fixed it and it began bogging down more frequently at lower RPMS and on right turns.

I figured it out tonight after getting a pressure gauge at autozone. Found that on start up at idle and with wot the pressure was steady at 39 psi. took it for a spin and checked pressure again; needle was bouncing all over the place. Let it idle for a while and it progressively got worse. It wasn't until the downswing dipped to 15psi that the engine stumbled. I tested voltage to pump and there was plenty of power when pressure was dropping (13volts I know that's high, may have to look at that later).

Installed a new fuel pump, NEW PUMP SCREEN, and new fuel filter. Problem solved.:roll::roll::roll:

THANK YOU!!! to everybody who offered advice!