DESERTXJ206

Hello guys I havnt been on in awhile. Iv got a bucking problem with my 1988Xj.

First off here's what happens: Randomly while driving at any speed under 55 I get a buck. Its not constant, it doesn't buck more than once. Its a quick buck. There have been trips where it happens 3-4 times in a single trip but it does not buck and keep bucking when it happens.

Here's what I've done to try and solve this issue:

Test fuel pressure and regulator with gauge. At idle its perfectly at 31psi and when I remove vac line it goes up to 39psi.
Drain and fill of the trans fluid

Replaced these:
IAC, plugs, wires, cap, rotor, tps.

I do not know where to look next to fix my issue.

Radi

Like the engine drops out for a split second? My '96 started to do that, changing the CPS and TPS fixed it.

DESERTXJ206

Well yes it feels like the engine cuts out for a split second or like it slipped gear and quickly 're entered that gear.

Iv done most of the sensors but never did the cps. Partly because the previous owner rigged in a new pigtails clip so ill have to get a factory pigtails to wire in before I get a cps.

I also have a rough uneven idle and at times while idleing it will cut out for a second like its going to die, then make its way back to steady again.

Cyriac

I have the same issues, I'd love to hear a solution to this. I have an 89 with a 5-speed and this is definitely engine and not transmission related. Could there be a misfire in one of the cylinders?

freegdr

Check for corrosion on fuel pump resistor terminals mine was doing this two weeks ago I cleaned the corrosion off terminals no more bucking since.

DFlintstone

That ceramic resistor Freedgr mentions is on the inner fender by the air cleaner. You can even by-pass it if you like. With a digital meter you can check your CPS in just a couple minutes:

AC voltage CPS test; Small clips on the meter leads really helps. (you need contact with those little pins while it cranks)

Unplug the connector at the back of the manifold with wires going down to the bell-housing/cps. (it's a three wire plug, with only two wires)
Probe the two wires to the cps with the meter set on AC volts. (a 200 scale on mine).
Crank the engine and note the voltage. (jump it if your battery is low)

Mine somehow works with only .3 my wiring/grounds must be pretty spiffy. .5 seems to be a good mark. One article talked of .5 to .8. **Update, it soon failed. I installed Napa #css980 in my 90, that part will work back to 87. You can also check for 200 Ohm's resistance, +/-- 75, (Hot), but the ACV is what the ECU is using.

DESERTXJ206

Ill have to check that out. Yesterday I added some Freon and while I was doing that a heard a grinding bearing sound. On the way home the water pump shaft decided to fail and turn sideways and chew into the pump housing causing all kinds of issues and blew all my coolant out.

So that's a project for tonight after work, then while picking up my wife in my civic I pulled into her work and steam started pouring out of the hood and the radiator has decided to go out too.

So that's $250 worth of parts and coolant between both vehicles I will be fixing tonight/tomorrow. Go figure.

sandaddik2

Check your cps wire coating for damage.

Mine was rubbing somewhere on the bell housing and rubbed through the coating.
This caused the wire to touch bare metal for a split second shorting it out and causing what you are describing.
I wrapped it in electrical tape and p-clamped it in place and ran it like that for the next 40k miles.

DFlintstone

Boy, maybe something in the water? Some issues are more not fun than others. Yours are right in there! If you keep taking two steps forward for every one back, eventually you will make progress.

Yea, I found my CPS insulation had sort of "dissolved", right by, and into the CPS it's self. Was a unit I put in for the PO around Y2K.

DESERTXJ206

I haven't had a chance to look into that stuff yet, as soon as I got home from work I started ripping apart everything to get the water pump out. The pump shaft shifted about 1/8th of an inch sending the fins of the pump into the pump itself and shaving pretty deep down into the pump. You cannot turn the pump by hand without it digging into itself. Thats the last "Reman" part like that I buy. The new pump is in and the black rtv is curing overnight, I will finish the install in the morning.

As for the Cps wires, when I was having other issues Cruiser54 had me test my cps and I found the previous owner had hacked the cps end and replaced it with some other sort of pigtails. I will follow the wires and see if I see any insulation breaks or damaged wires.

Does anyone have a quick picture of the thing on the fender that you guys were talking about? I quickly glanced over the area before tearing into it tonight but didn't see anything abnormal without taking wires and such apart.

Sorry for the sideways pics, the first one is of the old pump cutting into itself by the pulley. Second is the fresh pump awaiting reinstallation of everything else!

DFlintstone

Cruiser has a pic somewhere. It's ceramic, with orange wires, on the inner fender near the air cleaner.

Unusual to have a CPS "Bypass" on a 90. It's plug would be a three wire plug, with only two wires.

DESERTXJ206

This is a 88' and I dont think it was bypassed. I think the P.O. maybe damaged the connector and spliced in a new one that was from something else.

DESERTXJ206

Well after the water pump swap I cleaned the connections with some sandpaper on the ceramic thing on the fender. Iv only drove the jeep a couple miles so im not sure if that was related to my issue.

freegdr

Has it bucked in those couple of miles ?

DFlintstone

Jeep sold a "kit" to bypass the C-101 connecter for the CPS wires on 87-88 Jeeps, mentioned here> http://www.bc4x4.com/faqs/yj.cfm?cat=5&faqid=164 (the "1990" on your info tricked me!)