So, I've been having a problem where part throttle driving is absolutely horrible. Cruising around town, half throttle will bog, but as you let up on the gas, it picks up. It would seem after 3300 rpm, it picks right up and works well. I put a new MAF on it which helped some throttle response, but the issue still remains.

I put a techII on it and it shows the MAF stop at 120g/s and continuing to press the throttle down doesn't change the value and it works bad. Once it hits a higher TP angle and/or 3300rpm+, the MAF jumps to 2XXg/s and works great. When it works good, the O2's are around .850 volts, but under bad working conditions the O2's are cycling, but it's too hard to tell where they are at.

It seems when the truck is in open loop, there is something maybe pulling fuel from the system? Once the truck goes into closed loop (heavy accel), everything seems peachy. Timing is also around 4* advance when working bad, but no timing retard being recorded.

I can't pull the data logs off the TechII to review them. No codes in the system. I did check the fuel pressure while running, and it was close to the numbers I found, but I'm not sure if they are right or not. Can someone verify the fuel pressure at idle?

Any thoughts would be appreciated, I'm at a loss.

 

Have you tried some injector cleaner. I had the same problem and I had the fuel filter replaced and put in a bottle of injector cleaner with a fresh tank of fuel. Seems to have sortted things out.

 

I had that happen to a car once and it was the fuel filter

 

Really? I would have thought a clogged fuel filter would give bad driveability all the time.. Maybe I should look into this.

I appreciate the feedback.

 

I would check the fuel filter first. Mine did the exact same thing yours is doing. It's been so long ago I can't remember hte speed it would bog down at but after it did bog down, the speed would increase as I let off of the gas. It was a new technique to getting on the freeway for sure!

 

its probably the fuel filter. does that tech2 tell you a/f ratio?

 

Installed a new feul filter and it still works the same.

The tech II doesn't show A/F, especially since there isn't an A/F sensor in the system. (2 front o2 and 2 rear o2 sensors) They cycle so fast I can't even get an average. If I could pull the logs off, I could step through it and see, and also possibly graph it.

The o2's stop cycling when it goes into closed look (aka wot or above 3500) and sit at .850 volts which is perfect under power.

 

Please let us know if you find out what is wrong. My 08 has been running exactly the same way. The dealer is not able to diag and fix

 

MAF sensors maybe or TPS sensor.

 

As soon as I figure it out, I will post up the fix.

No more Jeeps - I just put a new MAF in, no change really.