frustrated newbie

[optichris]

Hi All.

 

I have a 1986 Comanche with 2.5L 4x4 4spd manual trans. This truck started life as 2wd and I converted it over to a 4x4. I had the motor rebuilt and did most of the work myself. I am having trouble with the fuel injection system. The truck runs fine at idle (misses once in a while), but when driving and with throttle about 25 to 30 percent open, it looses power (does not quit) and acts like it is backfiring or coughing. If I go ahead and press the throttle further the engine returns to normal and speeds up. Here's what I have done:

 

replaced crank sensor

replaced TPS

replaced fuel pressure regulator (fixed a prior surging problem)

new fuel filter

new fuel pump

swapped coil/module with another used one I had

swapped MAP sensor with another used one I had

 

I have the factory fuel injection booklet. I checked the remaining sensors according to the manual and they check out fine.

 

Not sure if it effects it or not, but I have removed the EGR valve and replaced it with a blank off plate. The charcoal cannister has been removed also. The PCV valve was removed and the hole plugged. I ran the vacuum hose to the rear valve cover filter breather from the throttle body.

 

At this point, I don't know what else to try to fix the problem. The truck runs great otherwise. Any ideas? Thanks in advance. Your forums are a wealth of information. :bowdown:

[HOrnbrod]

O2 sensor functioning?

[optichris]

Back when this truck was carburated, I replaced the original 3 wire sensor with a 1 wire sensor so I could see if the truck was running rich or lean. I never switched back to the 3 wire sensor. Instead, I wired the signal wire to the proper wire on the ECU harness. Is it worth spending the money for the 3 wire sensor?

[HOrnbrod]

I would. Sounds like the ECU is not getting the correct signal from your O2 sensor over the entire RPM range, and is messing up the A/F ratio at 25-30% throttle. Or you could install have a tech check it out on an A/F meter.

[MJCanadian]

i'd say timing, check that out too

[JeeperjohnfromPA]

Sounds like a problem I had on my 91 YJ, (2.5 with a 5speed), it was a bad wire coming out of the coil, the connector there was fubard.

[optichris]

here's an update....

 

Yesterday I followed the troubleshooting flow chart found in the FSM. Even though I was missing a few pages, I am fairly confident that the fuel injection system is working correctly. All of the sensors and circuits to the ECU check out fine with the exception of the MAP sensor. The manual says I should have less than 1.0V with 20" Hg. I have 1.2V. I will hold off replacing the MAP until I check everything else out - like the wires to the coil. I know that the connector to the coil is melted, so it is definitely suspect. I also know that I have non champion spark plugs. I will change those out too, just in case.

 

One interesting thing that I found out through the troubleshooting is that the motor is running very cold...I think. Typically, it runs about 165-180 deg F. What is the proper operating temp for the 2.5?

 

I will post back with another update today after some more checking. Thanks for your help.

[Eagle]

Back when this truck was carburated, I replaced the original 3 wire sensor with a 1 wire sensor so I could see if the truck was running rich or lean. I never switched back to the 3 wire sensor. Instead, I wired the signal wire to the proper wire on the ECU harness. Is it worth spending the money for the 3 wire sensor?

???????

 

You said this is an '86. The 1986 MJ 4-cylinders were throttle body injected from the factory. Either your truck isn't an '86 or it wasn't original when you got it. In any case, how would you expect an EFI computer to properly regulate the fuel/air mix if you're not using the O2 sensor that's designed to work with that ECU? Oxygen sensors are not generic, one size fits all.

[optichris]

Here's the deal. After I did the 4WD conversion and rebuilt the motor, I put it all back together including the TBI. Immediately, I started having trouble with the truck surging and not idling. At the time, I took the half @$$ way out and installed a weber style carb along with a duraspark ignition module and different distributor. After some time with the truck running with the carb, I still wasn't happy. The truck ran fine, but the fuel economy wasn't good. Also the idle was a little rough. I knew that the only right thing to do (that was in my budget) was to put the truck back to the original TBI. So, here I am...

 

UPDATE: I took the connectors apart for the ignition module and cleaned them all out. It looks like the module/connector is fine. I also took the advice to check the timing. It looks like I may have had the distributor off by one tooth. I won't call the problem fixed because I didn't have time to test drive it. Now, I'm watching the Bucs football game... GO BUCS!

[optichris]

About the O2 Sensor - I am just out of college and also have just gotten married so I have little money and little time. I did some research and found out that O2 sensors modulate voltage between 0 volts and 1 volt. 1 volt being A/F rich, 0 volts being lean. What is different is whether or not the o2 has a heater. As far I as I know, the signals are the same, but the heater and plug are different. This truck is a bit of a patchwork - little of this and a little of that. I am trying to get it running the best I can with as little money as possible.

 

Thanks for everyone's help. You guys have given me some great suggestions.

[86FUBAR]

this is what i found out at NGK.com. the 3 wire

A 3 Wire Oxygen Sensor may also be referred to as a HEGO sensor (Heated Exhaust Gas Oxygen Sensor). Their operation is similar to 1 wire sensors, except they have an internal two wire pre-heater which enables the sensor to more rapidly achieve proper operating temperature. One wire carries the sensor signal while the other two wires supply voltage to the internal heater. Like a 1 wire sensor, the signal ground is achieved through the sensor body where it threads into the exhaust system.

and the 1 wire

A 1-Wire Oxygen Sensor may also be referred to as an EGO Sensor (Exhaust Gas Sensor) The single wire on this sensor delivers the signal while the ground is achieved through the metal sensor body where it screws to the exhaust manifold. This type of sensor was quickly replaced by the 2 wire sensor because the threads where the sensor screws into the exhaust can easily become corroded resulting in a degraded ground connection leading to faulty sensor readings. On the 2 wire sensor, one lead delivers the signal while the second lead is the ground.

 

it does apear that u can run a 3 wire in place of the 1 wire ,hope this helps

[optichris]

Well, two different test drives and it seems to be fixed... I changed the spark plugs to OE Champions and adjusted the timing. Keep your fingers crossed! Thanks everyone for your help.