Engine Stumbles under easy acceleration

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Nov 30, 2009 | 07:53 AM

bcompton35603

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Engine Stumbles under easy acceleration

I have a 98 Expedition 4.6 with 224,000 miles. Spark plugs, wires, and both coil packs were changed in March. Engine stumbles occasionally under light acceleration but if I put my foot in it, it smoothes out and takes off. I am wondering if I have some bad fuel injectors, and I am not getting any check engine lights. If it is fuel injectors, can someone send me a procedure to remove/ replace them?

Nov 30, 2009 | 10:31 AM

97ExpGuy

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From: Southern Illinois

Quote:

Originally Posted by bcompton35603

Hmmm...I gotta ponder this one for a while. Even though you had the plugs, wires, and COPs changed in March, let's not rule out that one might have failed - just for the sake of it.

For fuel injectors, with that mileage, I would go ahead and inspect them. To do it though isn't as bad as the plugs and COPs. Really, it's pretty straight forward: disconnect each connector on each fuel injector, remove the two bolts holding the chrome/SS fuel line on the intake manifold, and then pry up. It may require a little force as the o-rings on the injectors make a good seal, but they will come out. Once removed, inspect the tips of the injectors for any hairline cracks. If you see a crack basically what is happening is that fuel is not being sprayed directly into the cylinder. For me, I have having hesitation/stumbling at highway speeds on my injectors. I never through a code either for the injectors. I was very lucky as the injectors crapped out the same time I did my 100,000 mile tune up for plugs and wires so I took apart everything at one time.

Hope this helps.

Nov 30, 2009 | 10:48 AM

bcompton35603

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that sounds like what my Expedition is doing. Seems to stumble most at the 45-60 mph range, when it stumbles I put my foot in it and hit 70 MPH and back off, and it smoothes out for a while. If it is my injectors, when I floor it I am forcing mor gas in. I will try to look at it this weekend if it is not raining.

Nov 30, 2009 | 11:57 AM

97ExpGuy

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From: Southern Illinois

Quote:

Originally Posted by bcompton35603

One more thing: when you re-install new injectors make sure you put a little motor oil on the o-rings to ensure they slide in place easily and without tearing.

I got a set of remanufactured set of injectors off Ebay for like $150ish...it will be the cheapest way to go instead of buying new. The injectors were all FoMoCo/Bosch injectors that were flow tested to ensure they were a matched set. "PrecisionAutoInjectors" I believe was the name on Ebay. Out of Florida. I have 5k on my truck since install with 0 problems. Better yet, the injectors he sent me were an updated version with an open face instead of the nipple on the tip of the injector so this problem should never happen again.

Any question please ask,
Tom

Nov 30, 2009 | 12:41 PM

bcompton35603

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Does this system have a fuel pressure regulator? I had a Pontiac Bonneville that had the same problem, when the engine started to stumble the fuel pressure regulator was getting gummed up

Nov 30, 2009 | 02:10 PM

97ExpGuy

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From: Southern Illinois

Quote:

Originally Posted by bcompton35603

Does this system have a fuel pressure regulator? I had a Pontiac Bonneville that had the same problem, when the engine started to stumble the fuel pressure regulator was getting gummed up

If the regulator is what (and where) I think it is, it should be the round housing that's attached to the driver's side fuel rail over the number 7 cylinder. There should be one or two hex-head bolts holding it to the fuel rail and a rubber hose attached to the nozzle in the center of the housing. Simply undo both the bolts and it will pop off - and spill some gas!

I never bothered with the regulator when I did my tune up. Honestly, it's not that hard to access because it's on top. It may be a little crammed but not bad overall to change it. I'd inspect the injectors first. If they are cracked, change and drive the vehicle and see if the problem persists or not. If does, the regulator might be the next step.

To be honest, and this is my thinking, if the regulator is having problems keeping a consistent flow of fuel to the injectors, I'd think you be having more drive-ability problems then the slight stumbles you are referring to. I think your problem would be a lot more persistent in my opinion. With the mileage on your vehicle and if the injectors have never been touched, I'm still betting on the injectors. Please keep us posted.