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Amedee, Former ASE Master Tech
Category: Car
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Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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1999 Isuzu Rodeo: the next time it wo..runs perfectly..only starts

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I have a 1999 Isuzu Rodeo LSE my problem is that one time it will start and the next time it won't . No ryhme or reason had service station check it out they said when it runs it runs perfectly but they cannot find out why it only starts when it wants to.. HELP!



When the engine does not start, does it crank over and not start or does it not crank over at all?

Customer: replied 6 years ago.
Cranks over and just does not start. Service station said spark is there but fuel pump seems like it is dead. Then next time you start it all of a sudden it works again.



When the engine does not start, will it fire up with starting fluid? If so, maybe you just have a fuel delivery concern??


I would rec to start by checking the fuel pressure. Fuel injected cars are very fuel pressure sensitive. Fuel pressure is very important and must be within specifications! But if the pressure is low, it does not mean the pump is bad. A plugged fuel filter, a pinched line, and low voltage at the pump can contribute to low fuel pressure. All three must be check before replacing the pump.

Customer: replied 6 years ago.
Had it at service station they told me when the truck rolls over and starts that the fuel pressure is right where it is supposed to be. Just when it rolls over and does'nt start seems like the fuel pump has no power. Leads me to believe that there is nothing wrong with fuel pump becuase when it works it works correctly.



Thanks for the information. Have you actually checked power to the fuel pump when this is happening? If not, this would be the next step.

Customer: replied 6 years ago.
When the truck does not start at the fuse (at fuse under hood for fuel pump) test light pulsates does not have steady light.
Are you saying that the fuel pump fuse as low voltage when the engine does not start?
Customer: replied 6 years ago.
I have a test light that senses voltage when voltage is there it lights up I held it on connection for fuse for fuel pump under hood. When someone sits in car and cranks it over light pulsates but does not stay on.

THanks for the info!


It sounds like you are definitely on to something! Lets check for voltage at that fuse with a voltmeter to see how many volts are are actually getting.


Let me know!

Customer: replied 6 years ago.
I got 0 voltage wether key was on or when I had someone turning it over. All other fuse in that box are getting around 11 volts but fuel pump 20amp fuse reads 0.
And you checked with with a voltmeter?

Did you pull the fuse out and look at it?

IS this both sides of the fuse that is not getting any voltage?
Customer: replied 6 years ago.
Yes with Digital multi-meter set to dc voltage. There is no voltage on either leg of fuse for fuel pump. All other fuses have 11volts or better on both legs.
Ok.. lets go to the fuel pump relay and see if it activates when cranking the engine over. If not, lets check to see if there are two powers going into the fuel pump relay with the key on and cranking. Here is a wiring diagram.

Customer: replied 6 years ago.

I get 12 volts at front blade #30 whether cranking or not. Then I get 12 volts at left blade # XXXXX but only when cranking did this with relay unplugged and probe in blade connection on fuse box.



SO I take it the relay is not getting activated when cranking the engine over? IS the computer supplying a ground to trigger activate the relay?

Customer: replied 6 years ago.
Not sure what you mean by supplying ground.
Ok.. does the check engine light come on with the key in the on position?
Customer: replied 6 years ago.
DO you have spark when cranking?
Customer: replied 6 years ago.

Are there any anti theft lights or security lights on or flashing on the dash with the key on?

Customer: replied 6 years ago.
Does the engine run on starting fluid?
Customer: replied 6 years ago.
Not sure will have to pick up starting fluid and get back to you tommorrow. Is 9:00 p.m. and stores are closed. Do you just spray into air intake?

You got it!

Spray the starting fluid into the intake while someone cranks the engine over and see if she fires up.

If so, then we just have a simple fuel delivery concern.

If this is the case, it sounds to me like the computer is not grounding the fuel pump relay to allow power through to the fuel pump.
Customer: replied 6 years ago.
What does that mean new computer?
It is possible... but not very likely. Chances are the computer is missing a input signal to send out the signal to activate the fuel pump.
Customer: replied 6 years ago.
so that can be input by a dealer or is it something I can do?
We will be able to do some testing short of using a scan tool.
Customer: replied 6 years ago.
OK will get starting fluid tommorrow and will let you know after I get home from work, Thanks
You bet!

Customer: replied 6 years ago.
I am not exactly sure what just happened but I sprayed starting fluid in air intake it chugged a couple times then next crank it took off. Ever since then it starts everytime I have tried it fifteen plus times and even left it sit for five to ten minuetes then tried it and it started again. You think maybe it was just dirty or maybe clogged?
It think your fuel pump was stuck causing no fuel pressure...
Customer: replied 6 years ago.
You think I should run a tank of cleaner thru it?
Sure.. could not hurt!

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Amedee and 6 other Car Specialists are ready to help you
Customer: replied 6 years ago.
Yes I did Thanks a bunch.
You bet!

Thank you!
Customer: replied 6 years ago.
After all that it quit running again I got some electronic cleaner and cleaned all the sensors on the intake and then replaced the fuel pump relay. Then it fired up and have not had a problem since the except for the fact that the check engine light is now on but does not seem to harm anything. Other than that it runs great. Thanks again

You bet!

Thanks for the update!

Have a great night!