Engine Hiccup

I am having a problem with the motor at intermittant/random times. Its been doing it for a couple years, but rarely(once or twice monthly). Its becoming more frequent (every 5-10 minutes)

Under load or cruise the engine seems to hiccup very harshly. It almost feels like its completely reversing for a split second. The vehicle jerks back, the tach drops, the entire driveline bucks, and then its fine. If you were holding a cup of coffee it would probably spill (but then all coffee drinkers spill). It only hiccups once, maybe twice, for a moment, then runs fine. But it is a complete shutdown/reversal of drivetrain.

What its not; fuel starvation. Fuel pump failure or starvation is a very gentle loss of power, wouldnt even know it unless on the throttle.

89, renix, 4.0/auto, completely stock except for air filter and ford 8.8 (neither of which changed situation).

I am wondering about TPS and CPS, but dont know what they actually do, or the failure modes.

Any thoughts would be appreciated........

Had same problem on my 98. Check cap and rotor and replace if there is a lot of wear or corrosion. Also check connections to coil, replaced my cap and rotor and had loose coil connection. All good now. I would start there before tps or cps.

I would agree that tuneup hardware has to be up to snuff. Other than that, my first suspects (in this order) are the crank sensor and then the coil.

Sometimes these components get to the edge of spec when they start failing. I would definitely test both of them; easy enough to do. Resistance checks on both is what needs to be done. I don't have the coil test procedure handy but here's some information about the CPS.....
-----------------------------------------------------------------------

Crankshaft Position Sensor: Common Symptoms if bad:

*Both the fuel gauge and or voltage gauge may not work/display

*It is possible that you may see a No Bus on the odometer (on newer models only)

*You will have no spark. Fuel pressure may check okay but fuel won’t get to injectors

*For 96 + newer, sometimes the OBDII code reader has trouble connecting to /reading codes

*Crank sensors can be intermittent; "thermal failure" is pretty common. Means that the sensor fails when engine gets hot, but works again when cooled back down. Be aware of this when testing as if you have a sensor that suffers from thermal failure, it will probably test GOOD as soon as it cools down.
--------------------------------------------------------------------------------

CPS TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (A-B-C) looking into connector left to right with the part with the notch in the middle on the right) Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

CPS TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1

Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 - 275 ohms. If the CPS is out of that range by much, replace it.


Test # 2

You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.

I had an O2 sensor that would make my 88 buck right around 2000 RPM (plus or minus a couple hundred RPM). It actually was fuel starvation, in a fairly specific RPM band and in a specific vacuum range, it seemed to be worse with moderate to light acceleration.
Drove the Jeep dealer nuts, they didn't seem able to recreate the symptoms in the shop and I guess were too lazy to test drive it much. Actually the reason I ended up with it, The dealer sold it to me still funked up, cheap.

87-89's had the problems with the ignition crossfire. if the distributor hasnt been properly indexed, you may want to look into it. also a bad plug or plug wire can cause that

i had a similar issue with my '87. it would only do it when cold, and only within the within the first 15-20 min of driving. it wasn't nearly as "violent" as what your issue sounds like, but it was a sudden and complete "shut-off" kind of feeling, usually right as i was about to shift. drove me crazy for at least a few weeks. i finally just unplugged, cleaned, and reconnected every single electrical connecter in the engine compartment, including the big c-101 plug. it never happened again....:dunno: