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switching to external fuel pump?


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I have an '86 2.5 TBI.

 

Bad drivability issues right now (won't idle - bogs & sputters under load - smells rich, flooded) Checked the usual sensor culprits - MAP & TPS test fine. New fuel filter. Blew out the vacuum lines & checked for leaks. Compression test is good. New cap & rotor, plugs, wires. Cat & muffler are 3 months old.

 

Installed a fuel pressure gauge into the test port on the TB, and I'm getting about 10psi max. Tried adjusting the regulator, no luck. Pinched the return line, no spike in pressure. So I'm thinking the fuel pump has either sucked up crud and is blocked, or it's going bad. I'm going to drop the tank and pull it.

 

Now - if the pump has gone bad, this will be the 3rd pump it's gone through in a little over 3 years (and they all managed to go just after the warranty is up) As any MJ'er knows, finding replacements is a headache, and they've got expensive as well.

 

So ... is there a relatively easy way to switch to one of those cheaper universal electric pumps that mounts outside the tank, and still keep a functioning gas gauge and stuff? Anyone know of any good write-ups for it?

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I'd look for a root cause that's been killing your pumps. How are the grounds? Specifically the one behind the drivers side taillight? If the tank has crud in it I'd clean it, or failing that, replace it.

 

Honestly, I'm puzzled about it. The truck doesn't see any hard off-road use - it's a DD. I dunno if I've just had a run of bad luck or what - one pump was a junkyard pull, so I sorta expected it to fail. The last two have been cheapo remans. I do use cheap gas on occasion ... but I don't think that's what's killing them.

 

Last time I dropped the tank (about a year ago) the inside looked good, and the sock was clean. The grounds are good. About a year ago I replaced the wiring/sockets in the taillights and cleaned/replaced the ground in the process. (I also checked 'em again this time after reading threads on the issue).

 

I'll clean the tank this time ... but I'd like to avoid a swap if possible. I have the extra large MJ one, and I like the extended range for road trips.

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I'd look for a root cause that's been killing your pumps. How are the grounds? Specifically the one behind the drivers side taillight? If the tank has crud in it I'd clean it, or failing that, replace it.

 

Honestly, I'm puzzled about it. The truck doesn't see any hard off-road use - it's a DD. I dunno if I've just had a run of bad luck or what - one pump was a junkyard pull, so I sorta expected it to fail. The last two have been cheapo remans. I do use cheap gas on occasion ... but I don't think that's what's killing them.

 

Last time I dropped the tank (about a year ago) the inside looked good, and the sock was clean. The grounds are good. About a year ago I replaced the wiring/sockets in the taillights and cleaned/replaced the ground in the process. (I also checked 'em again this time after reading threads on the issue).

 

I'll clean the tank this time ... but I'd like to avoid a swap if possible. I have the extra large MJ one, and I like the extended range for road trips.

 

 

 

 

You get what you pay for.....When my fuel pump went I went threw 3 cheep aftermarket ones before I went to jeep and paid $160 for the OEM one and it still works fine :cheers: good luck

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I have an '86 2.5 TBI.

 

Bad drivability issues right now (won't idle - bogs & sputters under load - smells rich, flooded) Checked the usual sensor culprits - MAP & TPS test fine. New fuel filter. Blew out the vacuum lines & checked for leaks. Compression test is good. New cap & rotor, plugs, wires. Cat & muffler are 3 months old.

 

Installed a fuel pressure gauge into the test port on the TB, and I'm getting about 10psi max. Tried adjusting the regulator, no luck. Pinched the return line, no spike in pressure. So I'm thinking the fuel pump has either sucked up crud and is blocked, or it's going bad. I'm going to drop the tank and pull it.

 

Now - if the pump has gone bad, this will be the 3rd pump it's gone through in a little over 3 years (and they all managed to go just after the warranty is up) As any MJ'er knows, finding replacements is a headache, and they've got expensive as well.

 

So ... is there a relatively easy way to switch to one of those cheaper universal electric pumps that mounts outside the tank, and still keep a functioning gas gauge and stuff? Anyone know of any good write-ups for it?

 

9-14 psi is the fuel pressure spec for a for a 2.5 Throttle Body, your right in there where you are supposed to be. Ditto on what Pete said about the grounds. The terminals may also be corroded internally. Did you check the IAC? Ya might wanna check the fuel pump relay on the passenger fenderwell too. These trucks are much like a Ford Ranger at the Fuel Pump/ Latch Key system.

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9-14 psi is the fuel pressure spec for a for a 2.5 Throttle Body, your right in there where you are supposed to be. Ditto on what Pete said about the grounds. The terminals may also be corroded internally. Did you check the IAC? Ya might wanna check the fuel pump relay on the passenger fenderwell too. These trucks are much like a Ford Ranger at the Fuel Pump/ Latch Key system.

 

So my pressure's actually not off too bad? I had read psi was supposed to be 14-15 so figured 10 was way too low.

 

I was also suspecting a bad injector ... at idle, the injector basically drips, drips, onto the plate, but when I apply the throttle I can't see any spray ... but I just thought that was a symptom of low fuel pressure. How do I test the injector?

 

thanks for the tips & info.

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9-14 psi is the fuel pressure spec for a for a 2.5 Throttle Body, your right in there where you are supposed to be. Ditto on what Pete said about the grounds. The terminals may also be corroded internally. Did you check the IAC? Ya might wanna check the fuel pump relay on the passenger fenderwell too. These trucks are much like a Ford Ranger at the Fuel Pump/ Latch Key system.

 

So my pressure's actually not off too bad? I had read psi was supposed to be 14-15 so figured 10 was way too low.

 

I was also suspecting a bad injector ... at idle, the injector basically drips, drips, onto the plate, but when I apply the throttle I can't see any spray ... but I just thought that was a symptom of low fuel pressure. How do I test the injector?

 

thanks for the tips & info.

 

Service manuals usally call out 14.5 psi but they usually don't require constant adjustment. When they do it's more like you are down on power or running out of fuel.

Sorry I called this ICA above

IDLE SPEED ACTUATOR (ISA)

The ISA motor, located on the throttle body, is an

electrically-driven actuator that changes the throttle stop angle by

acting as a movable idle stop. The ECU commands the ISA to control

engine idle speed and maintain a smooth idle during sudden engine

deceleration. It does this by providing the appropriate voltage

outputs to produce the idle speed or throttle stop angle required for

particular engine operating condition. There is no idle speed

adjustment.

For cold engine starting, the throttle is held open for a

longer period to provide adequate engine warm-up prior to normal

operation. When starting a hot engine, the throttle is open for

shorter time.

Under normal engine operating conditions, engine idle is

maintained at a pre-programmed RPM, which may vary slightly due to

engine operating conditions. Under certain engine deceleration

conditions, the throttle is held slightly open.

ISA motor acts as movable idle stop to change throttle stop

angle. Both engine idle speed and deceleration throttle stop angle

are set by ISA. ECU controls ISA motor by providing appropriate

voltage outputs to produce idle speed or throttle stop angle required

for engine operating condition.

IDLE SPEED ACTUATOR (ISA) MOTOR

1) Adjust ISA motor plunger to establish initial position of

plunger only if motor has been removed or replaced. Remove air filter

elbow and start engine. Run engine until engine reaches normal

operating temperature. Turn A/C off (if equipped).

2) Connect tachometer leads to diagnostic connector D1,

attaching negative lead to terminal D1-3 and positive lead to

terminal D1-1. See Fig. 4. Turn ignition off. ISA motor plunger

should move to fully extended position.

3) When ISA motor plunger is fully extended, disconnect ISA

motor wiring connector and start engine. Engine speed should be

3300-3700 RPM. If incorrect, turn hex head screw at end of plunger to

provide engine speed of 3500 RPM.

4) Fully retract ISA motor by holding closed throttle (idle)

switch plunger inward as throttle is opened. Closed throttle switch

plunger should not touch throttle lever in closed position. If

contact is made, check linkage and/or cable for binding or damage.

Repair as necessary.

5) Connect ISA motor wiring harness connector and turn

ignition off for 10 seconds. ISA motor should move to fully extended

position. Start engine. Engine speed should be 3500 RPM for short

period of time and then decrease to normal idle speed.

6) Turn ignition off. Disconnect tachometer. After final

adjustment of ISA motor, use thread penetrating sealant (Loctite 290)

on adjustment screw to prevent movement and maintain adjustment.

 

To test the injector place a test light across the injector leads and crank the starter. The light should flash brightly, if it flashes dimly then disconnect the harness and check the resistance of the injector if less than 10 ohms replace the injector. If above 10 ohms the problem is most likely in the harness, find and repair.

 

Although, Dripping from the injector with the engine off is a pretty good indicator that the injector is shot.

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thanks a ton for the info, brigarpeon & pete. I'm headed back out to the garage this evening.

 

One clarification, though - when you say injector shouldn't drip when off, do you mean when engine is shut down, or simply at idle? Also, is there a way to test the injector itself to see if it's good?

 

Sorry about the noob questions ... but this is the first FI'd vehicle I've ever worked on myself.

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thanks a ton for the info, brigarpeon & pete. I'm headed back out to the garage this evening.

 

One clarification, though - when you say injector shouldn't drip when off, do you mean when engine is shut down, or simply at idle? Also, is there a way to test the injector itself to see if it's good?

 

Sorry about the noob questions ... but this is the first FI'd vehicle I've ever worked on myself.

 

Injectors should never leak into the environment, which I ASSuME is whats happening...

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Injectors should never leak into the environment, which I ASSuME is whats happening...

 

thanks, that's what I figured.

 

Just to be specific - what's happening with mine is:

No leaks when engine is shut off.

When engine idles, there's a small consistent drip from the bottom of the injector into the bore

When I depress the throttle, the drip just stays about the same - there's no noticeable spray.

 

I assumed that's bad - but I just didn't know if that was the symptom of some other problem (such as bad pump or pressure regulator)

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yeah you hook it up to a noid light and check the, oh boy, forgot the technical term. pulse width i think it is? someone help me out here. basically a light flashes. what you can do is go to napa and get some engine cleaner. clean the crap out of the area around your fuel injector get a new one put it on and if nothing changes bring it back say you don't need it no more. if it solves the problem then bravo

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thanks a ton for the info, brigarpeon & pete. I'm headed back out to the garage this evening.

 

One clarification, though - when you say injector shouldn't drip when off, do you mean when engine is shut down, or simply at idle? Also, is there a way to test the injector itself to see if it's good?

 

Sorry about the noob questions ... but this is the first FI'd vehicle I've ever worked on myself.

 

Read my post above again, I explained how it is checked.

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