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1989 MJ - I can crank it but it will not start. Please help.


NC-MJ
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Hello everyone! This is my second week as a Jeep Owner and I am hoping you guys can help me with my first problem. I have been reading this forum and I have found posts that are similar to my issue but the symptoms of my problem do not exactly match up with what others are experiencing. Let me give you a break down on what I have and what my problem is.

 

I am the second owner of a 1989 Jeep Comanche Eliminator 2WD 5SPD Short Bed with 126,000 original miles. The previous owner, a family member, stated that the truck started in the driveway but while in reverse backing down the driveway, the MJ just turned off and could not be restarted. There were no prior problems up until this point.

 

When I go to start the truck it will only crank but not start. Having read other owner posts, I checked/replaced the following items.

1. Fuel Pump- I am getting power to the pump and the pump is pumping gas. I put a 20 oz soda bottle over the fuel line and cranked one crank and almost filled the bottle up.

2. Fuel Filter- Replaced original filter and it looked normal for 126,000 Miles.

3. Pulled spark plugs and inspected them. All were in good order and we have ignition at the end of the spark plugs.

4. Checked distributor cap – Button looks good and points were in good shape.

5. Crank Position Sensor –Replaced original with new CPS. I can crank it but the motor will not start.

6. Fuel pressure regulator- I disconnected the fuel line before the FPR when. I cranked the truck thinking fuel would run out into my test bottle, but nothing happened. My next thought was that I might have trash in the line. I attempted to blow out the line with compressed air but I only seemed to get blow back from the fuel that was in the line mixed with the air. I cranked the motor again and still no fuel in the test bottle. I installed new FPR and still no luck.

 

I thought I would post to the Tech Forum before I spent any more money in the hopes someone here can point out the error in my diagnosis and maybe help me get my MJ back on the road.

 

Thanks for reading.

 

NC-MJ

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There are three things necessary for an internal combustion engine to run: fuel, air, and spark. Air's free, so we worry about the other two. You have verified fuel delivery, but not pressure. There is a test fitting on the fuel rail, you can use that to check for pressure. Since you say you have verified spark, and timing isn't adjustable, for now maybe we can assume that spark isn't the problem. So ...

 

Have you verified that the injectors are injecting? Gas in the fuel rail ir useless unless the injectors put it into the cylinders.

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Thanks Eagle and Carnuck for responding.

 

I was able to get the truck to turn over using the spoonful of gas in the throttle body suggestion. jamminz.gif As long as I kept my foot on the gas it would run. If I took my foot off of the gas pedal, the car would start chugging and then it would stall. I could only keep the engine running for 10 to 15 seconds at a time.

 

Eagle/Carnuk – From what I described above do you think my injectors are not working properly or do you think I have another problem which is preventing the MJ from running normally? What would you guys recommend for my next trouble shooting step.

 

Thanks

NC-MJ

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Gently purge the fuel rail (rag under the valve and gently push in the Schraeder valve without bending it so it won't stop leaking) and see what the fuel smells like.

 

(since it runs, this part isn't needed)

I bought a lawnmower spark plug tester for $5 (they have them in the cheap tool bin at work) so I can hook a plug wire to it to check for spark, but since it catches to run with a splash of gas, spark is not the issue.

 

 

A fuel pressure test gauge is the next step after checking the fuel in the line to see if it's rancid. Then check the engine and body ground points (take the wire off, clean and dielectric grease them) Too bad injector testers are expensive. I bought a set of noid lights (they check the harness to see if a pulse is coming to the injector)

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I checked the fuel smell tonight and it didn’t smell like gas but more like varnish. I siphoned as much as possible from the gas tank and added about 8 gallons of fresh fuel and two bottles of fuel injector cleaner. When I went to start the truck, it would turn over and run a little longer but if I took my foot off the gas, it still stalls out.

 

When I go to check the fuel rail to see if there is good pressurization, I get a small pressure leaking sound when I press the schrader valve but no gas shoots out as me. I guess I will definitely have to get a fuel pressure test gauge to see what the rail pressure is topping out at when the motor does turn over with the gas in the throttle body trick.

 

Is there a chance I have a clogged fuel line? Or is this possibility a failing fuel pump?

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Definitely sounds like a fuel delivery problem - something's gummed up. Replace the fuel filter as Eagle says. If this doesn't cure it, check the fuel pump flow rate. Connect a hose (an A/C hose works well) to the rail test port and put the other end in a bucket. Pinch off the return line, and crank it over. A good pump should deliver at least one liter of fuel/min; you can try it for 15 seconds and do the math. If it does not, since you have already replaced the the fuel filter, the pump is defective (clogged) or the inlet sock in the gas tank is clogged (most likely cause).

 

If you have good flow, the problem is most likely clogged injectors. Good luck. :D

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Eagle - Fuel Filter was replaced along with the Crank Position Sensor and the Fuel Pressure Regulator.

 

Hornbrod - I will give that a shot tomorrow and see what I come up with.

 

I appreciate all of the advice guys. I would love to get this truck back on the road.

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Too bad injector testers are expensive. I bought a set of noid lights (they check the harness to see if a pulse is coming to the injector)

 

Noid lights can be made cheap by the home mechanic! get a 5w tag bulb, (small push in bulb) bend the tabs down from the glass base of the bulb so you have two prongs sticking out, un-plug injector, plug in bulb (make sure its plugged in the contacts) hit the key and watch for flashing bulb

:idea:

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They are not all 5 watts though! Saw one guy take out his computer that way in an '89 Caddy..... in 1990 so a new computer was $$$$$$

the wattage on the bulb doesn't really matter, that's just the style bulb you use. we've been testing cars this way for years at the shop i work at. it definitely does not kill computers on jeeps, fords, volvo's, dodges (thats all the ones i've got first hand experience with)

 

can't speak for everything but i find it highly unlikely you would kill the computer this way

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I tested the fuel pump again to see if I was getting any fuel pumped from the back of the truck to the motor. I hooked up a hose and bottle to the fuel rail and I got a quarter liter worth of fuel from turning the truck over for 15 seconds or so. I hooked everything back up and did the “gas in the throttle body” trick and truck turns over for 15 or 20 seconds and then stalls out.

 

I went out and picked up a gauge to test the fuel pressure when I started to motor using the “gas in the throttle body” trick. I hooked up the gauge and turned over the motor for 15 to 20 seconds and when I went to check the gauge, I see zero pressure being registered. I retested about three more times and still no pressure is being read on the gauge.

 

My new question for the group is, and forgive me if my thought process is off here, but do you think the fuel pump is only strong enough to pump fuel without pressurization? I was thinking that if the pump wasn’t strong enough and could not pump fuel to a pressurized system then it wouldn’t be able to force fuel to spray out of the end of the fuel injectors. It also might account for the zero fuel pressure reading. :dunno:

 

Thanks!

NC-MJ

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Just an update guys. Thanks for all the feed back.

 

1. Fuel pressure regulator is brand new.

2. Fuel pump ground is clean. Still no dice.

3. Bypassed the fuel pump relay and the pump comes on and you can really hear it pumping. Still no dice.

4. Fuel Pump is the original unit so wires should be correct. If I do change the pump I will keep the wiring in mind as to not hook it up wrong.

 

One thing new today, I did notice that my ballast resistor was cracked in half and was free hanging from the fender. I have a new one on order. Do you guys think this is what is preventing the truck from turning over?

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My question for the group is, and forgive me if my thought process is off here, but do you think the fuel pump is only strong enough to pump fuel without pressurization? I was thinking that if the pump wasn’t strong enough and could not pump fuel to a pressurized system then it wouldn’t be able to force fuel to spray out of the end of the fuel injectors. It also might account for the zero fuel pressure reading.

:dunno:

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Pull the fuel line off the rail and see if it pours out of there like it did straight off the tank.

 

When tested the fuel pump in the past, I removed the fuel line right before the fuel rail. When I would try to start the truck, gas will flow through the line and start filling my bottle if I turn the ignition over. Fuel does appear to be entering the fuel rail.

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