problem with starting

Last night I rode my 87 comanche 4.0 to town and back with no problems. I woke up this morning and tried to start it, but it just cranks over and spits and sputters like it wants to start but doesn't. I pushed in the valve on the fuel rail and fuel came out. I haven't did any other tests on it though. Anyone have any suggestions that might can point me in the right direction?

Quick and dirty test...... spray some carb cleaner in the intake while cranking. If it fires up, it is a fuel problem. If not, you can rule that out.

spraying intake didn't help

Then you are left with spark, compression, and timing. Easy way to check spark is to get a screw driver( bare metal head and shaft) and stick it in the end of the wire coming from the coil to the distributer. Put the screw driver in the side the distributer goes and leave the coil plunged in. Get it about 1/2 inch away from something metal like the ac compressor or the block and turn it over and watch if spark jumps it. It should be a strong spark at that distance but if anyone else knows feel free to chime in


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If it isn't a fuel problem, the most common thing is the crankshaft position sensor.

Spark and timing originate with the CPS. Losing compression on all cylinders is extremely unlikely.

If the CPS does not fix it, I would look at the coil/ignition module.

what don't make sense to me is why it would work one day and not the next. doesn't a cps or any other sender slowly die out? as well as all the ignition and compression components? how do you check a cps also?

Get an ohm-volts multi meter and test the sensors ground wires versus battery negative post for more than 1 ohm on the ohms setting, engine off, power off. The 87-90 Renix Jeeps are notorious for bad grounds. Do that first.

Then back probe the 2 CPS connector pins and check the volts on the low volts scale. If under 0.50 volts you have a CPS problem, otherwise it is OK.

Check the plug gaps, check the rotor and cap for dirt, oil and wear on the electrode tips. Replace as needed.

On the fuel issue, you need to check the fuel pressure, should 29 to 39 PSI depending on whether or not the FPR vacuum line is attached. then check the vacuum line to Fuel Pressure Regulator (FPR) to see if it smells, or has fuel in it. If it does it the FPR is bad and is flooding the engine.

A stuck open fuel injector can cause rough starts and engine flooding. If flooded, crank the engine with the gas peddle at wide open throttle to the floor, that cuts off the fuel supply so you can dry out the cylinders.

Also check the battery voltage while cranking. The 87-90 will not crank fast enough (CPS -ECU issues) to start if the battery voltage drops under 10 Volts while cranking.

If all that fails it could be dirty loose contacts between the HV spark coil and ICM module under the HV coil, or bad ground there. Or one of them may be going bad.

Lastly make sure the vacuum line from the MAP sensor on the firewall to the throttle body just above the intake manifold is sealing and not loose or damaged.

That should be a good start. Have fun!!!

tylergrant2011 said:

what don't make sense to me is why it would work one day and not the next. doesn't a cps or any other sender slowly die out? as well as all the ignition and compression components? how do you check a cps also?

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Loose dirty ground contacts that move and get better or worse as they move is one common reason. The gang of them on the engine block near the oil dipstick are the most common gremlin sightings.

Also poor, corroded connections at the battery posts add to your grief. 87-90 Renix jeeps hate poor lose dirty grounds and there also issues with in the main harness on crimped sensor grounds that can cause problems. The Renix CPS will work when it wants to and not work when it does not want to, if the cranking voltage is between .26 and .49 volts.

Most CPS sensors for the Renix made nowdays and even the OEM sensors had issues, and we have a fix where you drill the mounting holes one hole size larger and mount the CPS a little closer to the flex plate/flywheel which boosts the output signal voltage. Crueser54 has the details here and now on his web site in his Renix tips pages.

With one of mine, though it's a 98, I'll drive it for a week then drive home for lunch one day and when I go to head back to workl, no crank. Having an issue with my battery terminals and cables. I'll bust out a tool so I can move the terminal a little and it starts.then runs fine again for weeks. And the terminals are quite tight. Takes a lot of force to move them. Not like they're loose. I'm afraid to over tighten them as I already broke two that way. Need to get cables and a battery ASAP I know.

Ecomike said:

Loose dirty ground contacts that move and get better or worse as they move is one common reason. The gang of them on the engine block near the oil dipstick are the most common gremlin sightings.

Also poor, corroded connections at the battery posts add to your grief. 87-90 Renix jeeps hate poor lose dirty grounds and there also issues with in the main harness on crimped sensor grounds that can cause problems. The Renix CPS will work when it wants to and not work when it does not want to, if the cranking voltage is between .26 and .49 volts.

Most CPS sensors for the Renix made nowdays and even the OEM sensors had issues, and we have a fix where you drill the mounting holes one hole size larger and mount the CPS a little closer to the flex plate/flywheel which boosts the output signal voltage. Crueser54 has the details here and now on his web site in his Renix tips pages.

Click to expand...

Hey thanks for the advice. I went back out and sprayed some ether in the intake and she fired right up and ran good for a few seconds. I managed to get it running by pulsing the fluid in every other second. I tried carb cleaner earlier today but apparently it didnt have enough go-go juice in it to make it run. All of this leads me to believe something with the fuel delivery. whenever i turn the key i can hear the pump priming. I also smelled fuel in the vacuum line of the pressure regulator. Anyone know where to buy or how to build a fuel pressure gauge relatively cheap?

http://m.harborfreight.com/fuel-injection-pump-tester-92699.html?utm_referrer=direct/not provided

I have this set and it works great. The set cost less than just a gauge and it has all the fittings you'll need to trouble shoot the fuel system

tylergrant2011 said:

Anyone know where to buy or how to build a fuel pressure gauge relatively cheap?

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Everybody still has them. Rockauto.com on line may be the cheapest, but you need to wait for it, delivery. Be sure to get a set of injector orings, 8 of them, and the two (or three?) for the FPR if they do not come with it (they should come with it) lube them all up with engine oil before installing them. It is located on the front of the fuel rail.

Be sure to label the injector wire pigtails before you pull the fuel rail. Do not disconnect the rear fuel line, it is PITA getting the plastic clip/o'rings for those and a PITA to install them.

Ecomike said:

Everybody still has them. Rockauto.com on line may be the cheapest, but you need to wait for it, delivery. Be sure to get a set of injector orings, 8 of them, and the two (or three?) for the FPR if they do not come with it (they should come with it) lube them all up with engine oil before installing them. It is located on the front of the fuel rail.

Be sure to label the injector wire pigtails before you pull the fuel rail. Do not disconnect the rear fuel line, it is PITA getting the plastic clip/o'rings for those and a PITA to install them.

Click to expand...

Before I buy anything other than the gauge is it certain that a fpr can cause a no start condition. also I recently changed the orings about 3 months ago in the injectors and fpr

tylergrant2011 said:

Before I buy anything other than the gauge is it certain that a Fpr can cause a no start condition. also I recently changed the o'rings about 3 months ago in the injectors and fpr

Click to expand...

If you see/smell fuel in the vacuum line and or feel/see fuel in/on the FPR male nipple (inside), the diaphragm is busted and leaking fuel into the vacuum line and can flood (rate depends on the leak rate) the engine and waist fuel and make it run rough. Try starting it with the Vac line disconnected and see if fuel is leaking out the FPR vacuum connection nipple. It may be part or all of the problem if bad enough. Probably part of the problem.

Also try cranking it with the gas peddle floored (It cuts off the fuel from the injectors, turns them off, in a starting operation) to dry it out in case it is flooded. Then try a normal start, and try it with the vacuum line disconnected and see what happens. If the FPR fuel leak is noticeable with the Vac line off, shut it off before you start a fire. Also you might be able to see the FPR leak just by priming the fuel rail with the vac line detached.

Test your fuel pressure at this point.

First chance you get, do Tips 1 through 5 at www.cruiser54.com.

Waynerd said:

I'll bust out a tool so I can move the terminal a little and it starts.then runs fine again for weeks. And the terminals are quite tight. Takes a lot of force to move them. Not like they're loose.

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Ive had that, its really weird...

Also, check where your distributor plugs into the engine wiring harness.

Waynerd said:

With one of mine, though it's a 98, I'll drive it for a week then drive home for lunch one day and when I go to head back to workl, no crank. Having an issue with my battery terminals and cables. I'll bust out a tool so I can move the terminal a little and it starts.then runs fine again for weeks. And the terminals are quite tight. Takes a lot of force to move them. Not like they're loose. I'm afraid to over tighten them as I already broke two that way. Need to get cables and a battery ASAP I know.

Click to expand...

Remove, clean and polish up the connectors and their contact points. Reinstall.