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Amedee, Jeep Technician
Category: Jeep
Satisfied Customers: 26268
Experience:  ASE certified Technician advanced level specialist. Wisconsin certified emissions state inspector
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Jeep Cherokee Laredo: I have a 1990 jeep cherokee laredo that

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I have a 1990 jeep cherokee laredo that stalls upon acceleration. I had a cranking problem last year and changed the cps and that solved it. The stalling problem occured later. I replaced the fuel filter, spark plugs and wires, Dist. cap and rotor.
The jeep sits alot, it is my sons and he is in the Air Force in Japan and is coming home on leave and I am trying to get it operational before he arrives.
The battery is weak and I have to use my jeep (96 classic) to start his. His battery is not recharging and the dash alternator charge display shows that it is charging at about 12 amps.

It sounds to me like you have two separate issues.

Which would you like to address first?
Customer: replied 5 years ago.
the stalling problem I guess
No problem!

Does the engine actually quit when this happens or just bog down?
Customer: replied 5 years ago.
It quits unless I keep the rpms up when putting it in gear
So it stalls under a load when accelerating.. correct?
Customer: replied 5 years ago.
Yes, I have to press the gas and hold the brake when putting it in gear to move. it does fine at idle.
You could have a fuel delivery problem. I would recommend to start by checking 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! You can get a fuel pressure gage at a local auto parts store for cheap.

Fuel pressure testing is frequently overlooked but it is one of the common causes of poor performance. The test procedure must include testing that will insure normal fuel pressure under all operating conditions.

Key Factors

1. Fuel demands are low at idle.

2. Wide open throttle at high engine revs uses the most fuel.

3. Fuel pressure must be reduced when manifold vacuum is high. Vacuum pulls fuel out of the injector causing it to deliver too much fuel if the pressure remains high. Manifold vacuum is used to open the pressure regulator at a lower pressure when vacuum is high.

A good way to check your fuel pump is to run an amp test on the fuel pump while it is running or while battery voltage is being applied ot it (turning the key on, cranking your vehicle or even when your engine is running. The amount of amps your fuel pump will pull will depend on how much fuel pressure your fuel pump should supply to your fuel rail. A good rule of rule of thumb for this test is as follows:

14 to 15 psi 3 to 4 amps

30 to 45 psi 4 to 7 amps

45 to 50 psi 7 to 8 amps

50 to 70 psi 8 to 12 amps
Customer: replied 5 years ago.
So at Idle it should be 3 to 4 amps? Could my weak battery/alternator be a contributor to this?
Your fuel pressure should be 40 psi plus or minus 5 psi. This would mean it would be between 8 to 12 amps.

The charging system should get fixed before you go any further.
Customer: replied 5 years ago.
It runs and idles fine when jump started..Does this indicate to you that it is just an old battery?
IT could.. but if the alternator is not charging, you might just need to replace the alternator and charge the battery. You wont know the battery is bad until you load test it with a battery tester from a battery store or at a shop.
Customer: replied 5 years ago.
I this battery took a charge at the auto store and I put it back in, would the stalling problem go away temporarily or would the weak alternator keep me from having the amps required. can I tell if the alternator is charging with my voltmeter?
YES.. you can check the battery voltage with the engine at idle using a voltmeter. Anything less than 13.5 and the alternator is not charging.

If the battery has gone dead for any reason or disconnected for any reason, then the computer will not time to learn the idle otherwise it will stall when putting it into gear like you are describing.
Customer: replied 5 years ago.
i have a 1996 jeep next to this one (good for camparison) The alternator is charging at 13.75 t0 13.9, the battery is still reading 11.8 to 12. (it started at 3.3)
I am so confused. Which Jeep are you talking about?
Customer: replied 5 years ago.

We're still on the 1990, sorry to confuse ya(the 96 has problems also, but we'll get to it later)

The 1990 is still reading 13.7 for the alternator and 11.7 for the battery. Would this cause the stall even if the altenator is good?

If the battery is reading 13.7 volts with the engine running, then the alternator is good.

This will not be your problem.

If anything, it was because the battery was disconnected causing the computer to lose memory
Customer: replied 5 years ago.
the battery is'nt reading 13.7, the alternator is. The battery post read 11.8 even while the enging is running. It started at 3.3.
Let is run for about an hour or so. See if the battery reading gets up to about 13.7 volts. If so, the alternator is just charging back up the battery. If not, you could just have a bad battery or a wiring issue between the alternator and battery.
Customer: replied 5 years ago.
its been running for about an hour and the best its reached is 11.8
You are going to need to start by getting the battery load tested. If it is bad or marginal, it needs to be replaced.

If that checks out ok, we check the wiring between the alternator and battery as well as the alternator inputs.
Customer: replied 5 years ago.
you said earlier that the fuel pressure gages were cheap. did you mean 50.00 for cheap?
I have seen them for even cheaper at sears and at other various places. If you want I can send you some link.
Customer: replied 5 years ago.

back to the original problem, (ok I probably need a new battery) but, if the alternator is charging properly, with the jeep running would the fuel pump be affected.

MOst of the time it will not. However, the higher the voltage the faster the pump will run. But just two volts higher or lower will not be a big deal to the fuel pump. It will still run..

I am glad I could help!

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Customer: replied 5 years ago.
How do I check my fuel pump voltage? I don't think I'm supposed to rate until i'm finished.
You will need to use an amp clamp with a voltmeter and clamp around the positive wire going to the fuel pump while it is running.
Customer: replied 5 years ago.

Can I check it at the relay?

You bet you can!
Customer: replied 5 years ago.
Help me out with the location. I'm having trouble finding it in the manual
The fuel pump relay is going to be located under the hood on the passenger side near all of the other relays and diagnostic connectors.
Customer: replied 5 years ago.
I got that far on my on but their not marked and the book doesn't even show them. which one is it. got a pic?
I cannot send any pictures because it is against copy write laws.
Customer: replied 5 years ago.
which relay is it
It will have a yellow wire, red wire and two orange wires
Customer: replied 5 years ago.
there's only 4 relays, do u know which it is
You will have to look at the color wires going into each relay to figure out which one is the fuel pump relay.
Amedee and 5 other Jeep Specialists are ready to help you
Customer: replied 5 years ago.
the ones I can see don't match that and I can't see the others.
Its there.. keep looking.
Customer: replied 5 years ago.
well this isn't helping, thanks anyway.
You bet!