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87 XJ 4.0 Hesitation problem

mark268

NAXJA Forum User
Location
Indiana
here is my problem. Possibly some of you can give me some details of what is happening.
It starts and runs well 125k on a 1987 4.0 has a slight hesitation when you press throttle rapidly. Seems like it has the power no noise, no leaks, pretty good runner but it does have the hesitation. So far I have not noticed any loss of power and the power is there when you ease on the throttle, but if you step on it quickly it has a definiate hesitation.
 
An injector cleaning could be the issue if you can confirm the pressure in the fuel rail (the regulator has a vacuum fitting to increase the pressure a few PSI for instances of rapid throtthe opening - intent is to provide a temporarily richer mixture while the ECU sorts things out... a weak pump, bad regulator or partially clogged injectors can cause this if your ignition componants are all in good working order)
 
OK, a little more info. It has been sitting for nearly a year without running. Changed the plugs and oild change already. Replaced the vacuum hose that has the PVC thing in it. Haven't ran it much yet. Just moved it in driveway and let it run at idle.
Cleaning injectors, should I have a shop do this or can I do it myself? I am mechanically inclined but never messed with injectors before.
I will take all the possibilities anyone can offer and do them
 
I put about 4 gal into it. I know I need to put fresh "clean" gas in ASAP. It only had maybe 1 gallon in it to begin with
 
Check all connectors in the engine for corrosion, and clean them. Then make sure the throttle position sensor is properly adjusted. ON my 87, too high an output voltage at the TPS caused that hesitation. At a later date it hesitated and stalled and that was cured by a thorough cleaning of the dreaded C-101 connector on the firewall.
 
throttle position sensor, C-101 connector, I have never heard of these. I hate the newer late eighties vehicles! Nothing like working on the old CJ darnit!
 
have you thought about changing the full filter everybody seems to forget about it
 
Start with the fuel filter (left side frame rail forward of gas tank) and TB/FI cleaning, and that takes care of the conventional weapons...

The TPS sensor is found near the throttle body. There is a small black sensor on the side of the tbody that will have 1 (M/T) or 2 (A/T) connectors off of it. There will definitely be one 3-wire, and there may be 1 four-wire for the A/T version. Check and clean these.

The C101 is on the firewall right next to the brake booster - make sure to remove the bolt in the centre of the connector (5mm I think) before you try to pull it apart, as it won't give first. Blast will with electrical contact cleaner or brake cleaner that <I> is not</I> non-chlorinated (sorry, but the green stuff isn't worth a damn on electrics...) and aply Ox-Gard prior to reassembly.

Also check and clean TPS harness connector, you will find near the driver's side rear of the block on top of the intake manifold. It is a 3-wire plug with only two wires in it, and one side will go right down the backside of the block (the CPS proper is at 1100 on the bellhousing...) This sensor generates basic fuel/spark timing signals, and this can cause all sorts of trouble for you. Average life is about 150Kmiles, but it usually fails all at once. An "intermittent" CPS fault is usually dirty connexions or the insulation on the wires shorting thru and grounding out somewhere else - and the latter is usually caused by vibration, so it will seem like a "stumble" under acceleration at first (I went thru this last month on my 88.)

Check all that, and let us know what you find.

5-90
 
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