Engine hesitation

[Jaime]

Hello everyone.

I've been a member of the club for a while now but have never posted anything. Usually I just do a search and get the answer I need, but not this time.

 

I have an 88 basic long bed truck with a 4.0 engine 5 speed manual transmission and a D35 differential. Pretty much stock I belive.

 

My problem is that the engine hesitates bucks and jerks after it sits for a while. In the morning I drive it for about 7 miles on the street no problem stop and let it sit for about an hour. Then I drive it for about 1/2 a mile thats when it starts to jerk.

 

Using the search feature here I tested the following and replaced them.

 

Fuel pump passed the pressure test but failed the pinch return line test so I replaced the pump and filter.

 

Fuel pressure regulator swapped with a used one but both past the test.

 

Manifold gasket replaced. When I did this I had to replace the O rings in the fuel injectors. Some started to leak so I replaced them all.

 

TPS replaced and adjusted to .8 volts going out and power going in is at 4.9

 

New plugs, cap, rotor and wires.

 

Any help will be greatly appreciated

Thank You

Jaime

[btm24]

sound like it could be your transmission going out maybe idk :dunno: but how can you have been a part of this for 4 years and never posted any thing? wow you must be a god at searching :bowdown:

 

Brandon

[HOrnbrod]

How was the fuel pump filter sock inside the tank when you replaced the pump? Dirty, gummed up? The inside of the tank could have lots of junk slowing fuel flow. Also do the rubber portions of the fuel pressure and return lines look okay? These hoses can collapse with age.

 

Might check for a cracked ignition coil as it can cause similar symptoms.

[Jaime]

I checked the fuel lines and they seem OK no cracks or spongy feel to them.

 

I did not see any cracks in the coil.

 

The fuel sock was brown and a little clogged up but the inside of the tank looked really clean.

 

I have a manual transmission I don't see how it could affect the engine but thanks for the suggestion.

 

Thanks

Jaime

[Oizarod115]

how's the wiring to the CPS look?

also, if it's original you might consider a replacement just for reliability-sake

[Jaime]

The wiring to the CPS looks OK and it was changed about 9 months ago.

 

Any other suggestions by anyone are greatly appreciated.

[HOrnbrod]

How did the plugs look when you changed them? All a relatively uniform color?

 

Try a voltage output test on the MAP sensor. Maybe it's going back and forth between open and closed loop. When is the last time you changed your O2 sensor?

[Jaime]

The plugs were in good condition and all uniformed.

 

I have not changed the O2 sensor since I got the truck about 4 or 5 years ago. Do you think that might be my problem and is there a way to check it before I change it?

 

I will test the MAP sensor in the morning and get back to you.

 

Thank You

[HOrnbrod]

The only way I know to test the O2 sensor is with an Air/Fuel (A/F) meter to verify it's doing it's job after startup to convert from open to closed loop. I'd say if you don't have an A/F meter, replace the O2 sensor since it's due anyhow. What's your gas mileage look like?

[Jaime]

No I don't have a meter so I'll change it tomorrow after work.

 

I can't tell you exactly my gas mileage since I have BFG 31's on the truck and have not changed the gear on the transmission. Just lazy I guess. My best guess is about 16 to 18 MPG.

[ratrapp]

the o2 sensor can definitly cause your problem.mopar actually recalled some o2 sensors from the comanche.i had the one on my 88 replaced free when i worked at a chrysler/jeep dealer about 9 years ago.

[Jaime]

The MAP tested at 4.9 key on power going in.

 

4.4 key on power going out. The book says 4.5 to 5.0 do you think I should replace it or is it OK.

 

1.4 truck started power going out.

 

I am still going to replace the O2 sensor tonight.

 

Thanks!

[HOrnbrod]

The MAP tested at 4.9 key on power going in.

 

4.4 key on power going out. The book says 4.5 to 5.0 do you think I should replace it or is it OK.

 

1.4 truck started power going out.

 

I am still going to replace the O2 sensor tonight.

 

Thanks!

 

I don't understand the 1.4V output with the engine running. It should be closer to 4.5V or so unless it wasn't warmed up enough to go into closed loop. Try changing the O2 sensor, run it for 3-4 minutes, then test the MAP output again. Oh, and be sure to use some sensor-safe anti-seize on the O2 sensor threads. :D -Don

[Jaime]

I changed the O2 sensor and engine smooth out until I turned it off and let it sit for a while. Then it began to do the same thing.

 

I retested the MAP sensor right after a 10 mile trip. With the ignition on and engine not running it read 4.5 volts.

 

I then turn on the engine and the volts dropped to 1.45 fluctuated to 1.5. I kept the meter on for about 3 minutes but it just kept going up and down 1.45v - 1.5v.

 

The FMS says with hot idle condition it should be between 0.5 - 1.5 volts.

 

The engine seem to stumble a bit and that's when I see the fluctuation in the volts.

 

Thanks again

[HOrnbrod]

I then turn on the engine and the volts dropped to 1.45 fluctuated to 1.5. I kept the meter on for about 3 minutes but it just kept going up and down 1.45v - 1.5v.

 

The FMS says with hot idle condition it should be between 0.5 - 1.5 volts.

 

The engine seem to stumble a bit and that's when I see the fluctuation in the volts.

 

Thanks again

 

Ah yes, that's right - Renix. I'm sure you have seen this link: http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm but if not I'd test the TPS and CPS next. Can you "borrow" a compatible ECU to test with? It almost sounds like a heatsoak issue..........

[Jaime]

I've been looking for that page for a while. I had seen it before but could not find it.

 

I am not able to borrow an ECU. I might be able to buy a used one from a junk yard and hope it works.

 

What do you mean heatsoak problem and which part do you think is getting affected by it.

 

Thanks

[HOrnbrod]

Heatsoak is when a component gets hot and acts weird. For instance there was a factory recall awhile back concerning heatsoak on the #2 injector causing rough running and stalling. Jeep's fix was to place a heat shield between the exhaust manifold and injector rail. I believe this applied to the HOs only though. I put one on when I installed the 2000 intake manifold. Figured it couldn't hurt.