bdrummon

Hi guys,

I'm new to the forums. I've been searching through many posts, but I haven't found my exact problem. I just purchased a 94 XJ with ~204k on it. A few days after buying it I noticed that after driving for awhile it would start jerking/hesitating on acceleration. About a week later (before I made an effort to do anything) I was pulling into work and the check engine light came on right when it started bucking. I checked the codes and got a 27 (something about a fuel injector circuit not responding). The jeep also started exhibiting the jerky acceleration at all times at that point (not just when warmed up). I decided to go ahead and throw a new cap, rotor, wires, and plugs at it. That seems to have removed the CEL (at least it hasn't come back in a week since performing the tune up!). However, the jerkiness while accelerating is still there. Yesterday I replaced the TPS, no change. Today I did a fuel pressure test and it came back normal, 31 at idle with vacuum on the regulator and 39 without. However, when I turn the jeep off the pressure immediately drops to 5 psi. I tried to do the fuel pressure leak down test to determine whether it was the regulator or the check valve, but the pressure didn't change at all when I pinched the return line! It seemed to stay right at 31 psi? How is that even possible? The jerky acceleration is only really noticeable when you're going uphill or coming down pretty good on the accelerator. You can "nurse" the accelerator and avoid the jerkiness. What do you guys think I should try next?

Outlaw Star

Have you replaced the fuel filter?

XJRed96

check valve is likely at fault since it holds pressure after you block off the line. also proves you dont have a leaky injector. but thats not what is causing your running issue. the issue is likely caused by a faulty injector not opening as it should based on the fault you said you had. try doing an injector upgrade (link here) and see if that makes a difference.

bdrummon

Oh yeah, I should have mentioned what I did about the injectors. After getting the CEL about the injector circuit I listened to each one with large screwdriver. They all sounded like they were actuating. I also borrowed a noid light kit and tested each connector, they were all getting a pulse. I've ordered some 703 injectors (for way too much, but I couldn't find ANY at the local JY). Hopefully the upgrade will solve the problem. Sounds like I might need to replace the fuel pump as well.

XJRed96

if you are getting steady pressure while running and driving from the fuel pump then i wouldn't rush out to replace it. just do the poor mans prime when you start the truck to avoid extended cranks.

Drinkjp8

Mine is a 92 and it's doing the same thing. It would either start up fine and drive fine for a bit then sudden jerks and hesitation and would come and go or be fine or not go away. Or it would start up jerking and hesitating and never go away or sometimes would but come back. It feels like a misfire and sounds like an exhaust manifold leak. I started with the plugs wires cap rotor and coil. Went to a single platinum plugs. Accel wires coil cap rotor. No change. Changed the FPR. No change. 703 injectors. No change. New fuel pump (low pressures even with new FPR) no change. Some mechanics tell me it's the computer. Some tell me that it's because of the exhaust leak. Even though I buy parts at cost price because I work at a parts store. I'm tired of dumping money into it. I just can't figure it out.

Click-Click-Pull

I know you said you just did a tune-up, but pull the plugs and check for any deposit changes. That may at least narrow down which cylinder has the issue. Good Luck!