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Chugging! Not surging...

Frank Z

Frank Z

NAXJA Forum User
Location
Colorado Springs
So my wife and I paid a visit to YellaHeeps House-o-Heeps today to pick up some doors for the heep. Heading back to Co. Spgs from Denver we got stuck in some weather related traffic on the highway and started noticing some weird vehicular behavior. At 2k on the RPM-ometer (Tach) and 40 on the speedy-o-meter the XJ would chug. WTF does chug mean? The exact opposite of surge. Not a quick random increase in power, but a sudden drop in power. It's very noticable in the seat of the pants...literally. My fat keester would move forward in the seat as the heep suddenly slowed down.

After we got off the interstate I tried a variety of gear choices, RPM's, and speeds. The problem is very evident at 2k and 40 MPH in either Drive or 3rd. A little slower and fewer RPM's...no chuggin'. A little above 2K...no chuggin's.

No OBDII error codes either.

Anyone else ever experience this?

What was the root cause and what was the repair?

Incase it matters to ya....
97 XJ
4.6L Stroker (Apprx 15k on it)
AW4 Tranny New filter and fluid about 20k miles back
New Distributor
New Crank Position Sensor
New fuel pump and filter about 1000 miles ago.
DexIIi in the Tranny
Rotella15w40 in the crankcase
35's and 4.88's
 
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No,fast answer for ya. But If I new alittle more maybe. Can ya check fuel PSI when it's acting up?
 
Does it seem like an ignition miss of a fuel issue?
 
If it's not setting a code for OBDII, it's most like NOT a sensor issue. It could still be a fuel or ignition issue that only occures under load.
 
no load, Injectors don't need as much fuel, under load, they need more. I reread you OP. So does it clear up after you get above the rpm, mph range or are you unable to get over those.
 
look closley at the wires. If you have reused the wires after a dis. cap or plug change it can mess them up easily.
How does that Rotella crank on cold mornings? No 5w-40 available?
 
So, correct me, it comes out of it after 4k RPM. How old are the plug wires? And WTH are you doing with a 4.0 at 4k and above ? Drag racing? I do 1850 at 60 mph. Just asking is all.
 
ia green96 said:
no load, Injectors don't need as much fuel, under load, they need more. I reread you OP. So does it clear up after you get above the rpm, mph range or are you unable to get over those.
Click to expand...


This guy has no friggin' clue......

Fuel pressure stays constant. The fuel pressure regulator ensures that it stays at a constant PSI - the injectors require a constant PSI just to operate. When the engine demands more fuel, the injectors cycle longer and the regulator allows for more fuel flow....... at a constant pressure.

Stroker motors require more fuel and usually you stroker guys go with "larger" injectors...... but the operation stays the same -constant pressure regardless of engine performance.

The fuel return line/system handles the return of excess fuel at slower engine speeds........

:twak:
 
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Frank,

Your symptoms sound like a TPS going bad. They don't set error codes often unless they're really bad. My '93 did exactly what yours is doing, but at a lower rpm - just off idle when cracking the throttle. It's a positional thing.
 
??? He said 2000 RPM at 40 MPH???

It still sounds like the TPS is dropping out. Have you looked at the pedal position? I don't know nothun about the newer heeps, how about torque converter lock-up letting the engine lug?
 
I know you have a new CPS, but the only time I've experienced a "chug" was when the CPS wires got too close to the exhaust header. The RPM may only seem to be related. FWIW.

Fred
 
YELLAHEEP said:
This guy has no friggin' clue......

Fuel pressure stays constant. The fuel pressure regulator ensures that it stays at a constant PSI - the injectors require a constant PSI just to operate. When the engine demands more fuel, the injectors cycle longer and the regulator allows for more fuel flow....... at a constant pressure.

Stroker motors require more fuel and usually you stroker guys go with "larger" injectors...... but the operation stays the same -constant pressure regardless of engine performance.

The fuel return line/system handles the return of excess fuel at slower engine speeds........

I'm sorry if you differ with my post, I'm a diesel tech and was trying to help out out a fellow jeeper. on diesels the regulator/ check valve is on the return side, so if you have injector acting up, It all goes back to the tank and the rail never get's psi.

I'm finding it odd that it only happens at 4k RPM and comes out of it. But it doesn't do it under load. Slill seems like ignition to me, but wtf do I know as you stated.

:twak:
Click to expand...
 
ia green96 said:
I'm finding it odd that it only happens at 4k RPM and comes out of it. But it doesn't do it under load. Slill seems like ignition to me,
Click to expand...

Well, that's where you're actually correct. The TPS controls the ignition in concert with the other sensors in the system. When the TPS develops a "flat spot" inside the mechanical operation of the sensor, it stops sending signal to the computer and thus, shuts down spark and fuel - and results in the loss of power Frank is experiencing.

Ya dig?


And yeah, Diesels do have vastly different fuel injection systems than gas injection systems. Diesel theory isn't going to apply to our XJ's - well, only in the rarest of occasions anyway..... :D
 
A long shot here,...but check to see if your distributor hold down clamp is tight.
 
Frank Z said:
.....I'll take any and all suggestions....sorta.
Click to expand...
OK Frank, about these "new" parts: Are they still under warranty? You DO have extras on stand-by...don't you? I mean, You ARE Frank_Z! LOL
 
YELLAHEEP said:
Frank,

Your symptoms sound like a TPS going bad. They don't set error codes often unless they're really bad. My '93 did exactly what yours is doing, but at a lower rpm - just off idle when cracking the throttle. It's a positional thing.
Click to expand...
X2 I had the same problem. Replaced the TPS and POOF! gone. Worth a shot it's only about $50.00
 
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