1987 4.0 Auto 4x4 - Engin miss.

[stonehands]

I have come a long way with this truck since I first posted its many problems. Down to just one now.

The #%$& thing has a miss at all rpms.

New wires, plugs, cap, rotor. Checked all sensors except the one on the bellhousing. Crank Position I think.

Can not change timing on this engin.

I do hear lifters a little as engin picks up rpms. Don't know what If any sound should be made.

No vacuum leaks as far as I can tell. Checked everything. Has 17 what ever designation it should be of vacuum.

Tighten manifold bolts.

Spark pattern using timing light on each plug one at a time shows consistant flash pattern no noticable breaks in flashes.

Don't know if poor injecting can cause this or not.Have not tested fuel pressure.

Checked sensors to specs in book except one listed above. All look good via the multi-meter.

Checked compression on 4 inner cylinders. If leak between cylinder would have shown for cylinder closest to outers.

Did not check outter due to space constraints. Could be leaking at exh. valve.

No backfiring. Did backfire when electronic boxes on drop panel in dash were not connected. When reving engin. Does not when all is connected.

Cruise control does not work.Don't know if this can cause a miss. Don't know jack about cruise on this thing. Found vacuum ball in bumper pulled out and mounted in space where old coolant bottle use to sit by blower motor. Made sure all vacuum lines to it were good and no leaks. Replace close loop with open. Mabey something there I didn't do that I should have?

 

Well there you have it. What I have done so far trying to find the problem. My suspisions are Injectors/pressur,valve/lifter, or crank sensor. What do any of you think. Tired of typing now-chow.

[tugalo]

A couple of possibilities, remove and thoroughly clean all grounds and/or install HEAVY duty new ground wires. Add one between the battery and the front clip. Sometimes the sensors give bad info to the computer due to high resistance grounds.

As for the cruise, there is a switch HIGH up on the brake pedal arm, it is hard to see and harder to get to...this switch releases the vacuum to the vacuum servo when you are in cruise and tap the brakes...if it is bad or out of adjustment, you will never get vacuum to set the cruise. Pull off the largest hose to the cruise vacuum servo and plug the outlet on the servo, if the cruise works, then you know something is wrong with the switch. Be careful if you do this cause you will have to turn the cruise off with the switch, the brake pedal will not cut it off. If you have an auto, the switch also has an electrical side that tells the torque converter to unlock. Good luck

[oldrusty]

Have you replaced the injectors yet? If not that would be my guess. My 89 developed a miss not long after I put it on the road that wound up being a bad injector. I replaced all the plugs, wires, cap, and rotor before I checked the injectors. Wound up having one bad injector. On the up side the truck got a tune up it probably needed anyway.

[BLHTAZ]

CLICK HERE for fuel injectors. When you make your purchase, use ' JEEP ' as the coupon/discount code for 10% off ;)

 

The only other thing that comes to mind on the running issue is what happended to me. When I bought my truck, it had a slight valve train noise and a miss...it ended up being a broken valve spring. $3 part and $30 to the engine guy to fix it.

[carnuck]

Once in awhile a push rod pops loose too (that's what's wrong with the '80 AMC Eagle wagon I just bought) Collapsed lifter or cam with a flat lobe is annoying too.

 

Make the plug wires loose at the cap and pull/replace them one at a time till you find the one that makes no difference. That helps narrow down the culprit. I then undo the clips holding the injector connectors on (or at least the one to the "dead" cyl) and check for signal by unplugging them while running. Sometimes it can be as simple as the connector to the cylinder next to it was swapped so the fuel sprays at the wrong time.