Need help 1998 4.0

Post by **shmoken875** » Tue Sep 01, 2009 7:21 pm

Hopefully I can get some ideas here, can't afford to throw too much money at the heep

-will drive OK for a few minutes then the following will occur, then will drive OK for a few minutes
-surging on road intermittently, low rough idle sputtering, NO power in low rpm
-if given little throttle under the hood will dog down and stay that way but not conk out
-CEL gave 3 codes, high voltage on both oxygen sensors, and bad O2 heater
-replaced oxygen sensors and CEL was still on, throwing same 3 codes, problems still there
-replaced 15A heater fuse under hood and CEL went out
-still have surging on road intermittently, low rough idle sputtering, NO power low rpm but CEL is gone
-sprayed TB cleaner (TB is very clean though) and idled OK for all of 20 seconds then went back to crappy idle

I'm left thinking about TPS, IAC and CPS for issues. Help?!

97JEEPTJ · Post by **97JEEPTJ** » Tue Sep 01, 2009 7:32 pm

I had some mysterious issues a while after I first got my Jeep, determined it to be the CPS. The engine would just turn off while driving, gauges would go down to zero, but the lights would still stay on. And sometimes it wouldn't start back up. The wires to the CPS were underneath the intake /exhaust manifold getting burnt up.

If the engine isn't completely turning off, I would rule the CPS out. Easy to check the wires though.

The guys on JF are good at diagnosing that kinda shit.

Question for ya- Have you disconnected the (-) battery cable for a bit of time to let the computer clear the codes? Maybe it would clear stuff up.

Post by **shmoken875** » Tue Sep 01, 2009 7:39 pm

97JEEPTJ wrote:I had some mysterious issues a while after I first got my Jeep, determined it to be the CPS. The engine would just turn off while driving, gauges would go down to zero, but the lights would still stay on. The wires to the CPS were underneath the intake /exhaust manifold getting burnt up.

If the engine isn't completely turning off, I would rule the CPS out. Easy to check the wires though.

The guys on JF are good at diagnosing that kinda shit.

Question for ya- Have you disconnected the (-) battery cable for a bit of time to let the computer clear the codes? Maybe it would clear stuff up.

-Yea I read that typically if its the CPS the engine will just shut off like that, but I've also heard they can just act up though.

-Yes disconnected the battery cable in the cage this afternoon and the CEL came on again 5 min later, thats when I read about the 15A fuse and replaced it, which turned off the CEL almost immediately.

97JEEPTJ · Post by **97JEEPTJ** » Tue Sep 01, 2009 7:41 pm

Gotcha. Check the wires to the CPS.

The actual sensor was only held on by one bolt on my bellhousing, sometimes it is 2 bolts. It's fairly cheap too.

97JEEPTJ · Post by **97JEEPTJ** » Tue Sep 01, 2009 7:42 pm

http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm

Check this link out about sensors.

YouTube · Post by **TerryD** » Tue Sep 01, 2009 9:42 pm

Kinda sounds like the TPS or MAP sensors or possibly the fuel pump going bad. Get you a fuel pressure checking gauge (I think Advance rents one) and see what you have vs what the repair manual says you should have.

Either the TPS or MAP sensor will cause a problem like that. It's when the engine is seeing a change in manifold vacuum vs load and the computer isn't seeing the change. You'll get a bog.

Post by **Fonger** » Tue Sep 01, 2009 10:15 pm

You may also check your fuel filter. Also, is it possible that you got a bad tank of fuel? My recommendation is to check the easy and inexpensive stuff first like fuel filter etc... You may want to check out some stuff called Sea Foam. We use the stuff all the time up here. Put a little in the fuel a little in the oil and suck some through a vacuum line and watch the smoke show. Just read the directions on the can. I'm tellin' you the stuff works wonders.

Post by **shmoken875** » Wed Sep 02, 2009 9:59 am

Fonger wrote:You may also check your fuel filter. Also, is it possible that you got a bad tank of fuel? My recommendation is to check the easy and inexpensive stuff first like fuel filter etc... You may want to check out some stuff called Sea Foam. We use the stuff all the time up here. Put a little in the fuel a little in the oil and suck some through a vacuum line and watch the smoke show. Just read the directions on the can. I'm tellin' you the stuff works wonders.

-filter replacement was easy on my 95 unfortunately in the 97+ cherokees the fuel filter and pump is all one module that is in the tank itself and costs $150-300 depending on mfg. I'll definitely check the pressure at the schrader valve on the fuel rail like Terry said and see if there's an issue

-I'll put a 1/2 tank in but the problems been getting progressively worse since Rausch Creek about 3 weeks ago and I've used WAWA, CITGO, GAS MART, and EXXON fuel.

-I'll definitely try Sea Foam though too, willing to try anything cheap first

-If it comes down to it maybe I can borrow TPS, MAP, and IAC sensors off another xj for a few minutes to see if it helps

Thanks for the help thus far Wilfong/Terry/Jake (that websites pretty informative), I'll let you know what I come up with

Post by **shmoken875** » Wed Sep 02, 2009 10:05 am

FORGOT TO ADD:
-over the past year or so maybe about once a month or less my xj would bog down for roughly a second when cold and trying to turn out onto Patrick Henry, but be fine for another month or more

-When I was replacing the upstream O2 sensor I rounded it off and being frustrated and having class in an hour, took it to Auto Repair to have them remove it. He called and said the threads twisted off in the bung so I told him to weld a new one in. Instead of a new bung they welded a nut over top of the messed up bung, which pulled the O2 sensor back (out of the down pipe) by about 1/2", would this effect its operation?

Post by **Jwlman** » Wed Sep 02, 2009 10:12 am

shmoken875 wrote:
-If it comes down to it maybe I can borrow TPS, MAP, and IAC sensors off another xj for a few minutes to see if it helps

You can borrow what ever you need to from my jeep

Post by **shmoken875** » Wed Sep 02, 2009 10:28 am

Jwlman wrote:
shmoken875 wrote:
-If it comes down to it maybe I can borrow TPS, MAP, and IAC sensors off another xj for a few minutes to see if it helps
You can borrow what ever you need to from my jeep

thanks bud I appreciate it

Forgot about your engine

Post by **shmoken875** » Wed Sep 02, 2009 6:19 pm

OK, bought a fuel pressure checking gauge at Advance so if you ever need one, let me know. Definitely think its the regulator. Here's what I got:

Cold prime - 48psi - 2psi/10sec bleed down
Cold running - 48-52psi - normal high idle
Cold running - 42-58psi - bouncing
2000 RPM - 50psi - steady
5 min, 190*F - 38-62psi - bouncing, rough idle begins
8 min, 210*F - 36-64psi - bouncing, rough idle

So something definitely isn't right as Chiltons states pressure should be 31psi at idle. The in tank module contains the filter, regulator, pump, sending unit and screen. I'm thinking I might as well replace the whole thing since I've got 145k on this thing and its probably original. Thoughts?

EDIT: I have since found that spec for 98 HO 4.0 is 49 +-5psi, but the pressure still fluctuates too much and is out of spec

Post by **Piranha216** » Wed Sep 02, 2009 9:58 pm

mine was doing the same thing over the summer and it ended up bein the TPS. soon as i threw a new one in it was back to running normal

Post by **Jwlman** » Wed Sep 02, 2009 10:37 pm

shmoken875 wrote:

EDIT: I have since found that spec for 98 HO 4.0 is 49 +-5psi, but the pressure still fluctuates too much and is out of spec

Yea, I was gonna say that I set mine at 50psi when I set up my engine

YouTube · Post by **TerryD** » Thu Sep 03, 2009 8:47 am

Your fuel pressure looks OK Randy. Do you have a multi-meter? If so, the Chilton's book should tell you how to ohm out your TPS to check it and may even have a procedure to check the MAP sensor.