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Old 10-16-2017, 07:13 PM   #11
danielwd
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One thing I hope to see is improved gas mileage. I know this truck like the back of my hand being the original owner since 1994 and doing every single repair on it. It was sucking down fuel like I had never seen it do before. I never measured, but I swear I could see the needle moving. It was especially bad right before the throttle position sensor finally gave out. Hopefully that will drastically improve.

Thanks again to everyone for all the suggestions.
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Old 10-17-2017, 08:29 AM   #12
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If the fuel pressure regulator failed, the mileage would drop like a rock also. A friend had a 4.0 A*star, and it used to get ~19-20. All of a sudden, 10mpg, and black smoke. Regulator died, and pressure was high. The Chermans are proud of their parts, and the regulator was a product of their workmanship. And about $100... Made a big difference immediately.
If you check yours, at idle, removing the vacuum line should bump the pressure, and you should NOT smell fuel at the diaphragm port. If you do, the diaphragm is likely failed, and feeding fuel into the intake. If you have the 'returnless' system, I don't know the regulator style as it may be electronic with a 'fuel pump driver module' that fiddles with juice to feed the pump motor 'adjusted' electricity and so modulate fuel pressure. No diaphragm involved.
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Old 10-17-2017, 06:10 PM   #13
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That's good advice...I already checked the fuel pressure and it checked out.

It was definitely my throttle position sensor that failed. A failing/failed TPS will make fuel mileage tank, which is apparently what was happening to my truck. I checked my fuel regulator early on as you suggested and it checked out good.
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Old 12-06-2017, 10:23 AM   #14
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Another update. So this has been quite the adventure.

I was wrong all along, at least I think so.

Ultimately, the issue was a failed fuel injector at intake port #3. The complication of the issue arose because it was intermittent, making it seem like some of the fixes I accomplished, were actual fixes (when they really were not).

I did solve many codes that have been popping up for years though. So I guess there's always that.

Thankfully, I haven't really dropped much money, although I am entertaining the idea of replacing all the injectors. That would run close to $300 after taxes with aftermarket Autozone injectors. I know many would object to this, but I doubt I would be interested in OEM injectors because of cost. Plus every aftermarket part I've put on this truck has worked fine in the past.

Funny story, and you can please feel free to make complete fun of me because I know I am NOT a mechanic. I guess I mention this in case somebody else is following behind me chasing the same issues an error codes. So, after I took the upper intake manifold off the truck, I placed four pieces of paper towel wadded up in the holes on the lower intake manifold so no screws, etc... would enter and wind up in valves/cylinders.

The only problem was that I needed to relieve fuel pressure to take the fuel rail and injectors off/out.

So dummy me unplugs the inertia switch and cranks for 15 seconds...

...with the wads of paper towel still in the lower intake.

Just lovely.

I need no other evidence to support the idea I am not a mechanic than this bonehead move.

Thankfully, after removing the lower intake, the wads of paper towel did not make into the valves, but they did come awfully close.
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Old 12-07-2017, 08:25 AM   #15
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FWIW, FoMoCo injectors are not a common failure point. Not saying they don't fail, but it is uncommon. Personally I would not replace them if they are functional. Likely you will not note any change in performance as they are likely functioning to spec.
If you want to do something, you can have them professionally cleaned and checked, removed from the engine and sent off. Some will do the cleaning and poking around for $20 each. Some will even return the injectors along with a flow graph to show how balanced they are after the process.
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Old 12-08-2017, 02:14 PM   #16
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Quote:
Originally Posted by tomw View Post
FWIW, FoMoCo injectors are not a common failure point. Not saying they don't fail, but it is uncommon. Personally I would not replace them if they are functional. Likely you will not note any change in performance as they are likely functioning to spec.
If you want to do something, you can have them professionally cleaned and checked, removed from the engine and sent off. Some will do the cleaning and poking around for $20 each. Some will even return the injectors along with a flow graph to show how balanced they are after the process.
tom
Initially, I thought the injectors were fine based on an audio test with a stethoscope. I will admit, it was quick test, and the injector that failed was under the intake and difficult to get to with my stethoscope. So, as I said, it was a 'quick' audio test. I finally realized there was a problem with the injector after designing a hook tool with a piece of steel long enough to reach the plug-in from under the upper intake. I unplugged the injector with engine running rough, and there was absolutely no drop in RPM's; whereas, disconnecting the others greatly affected the RPMs. I had been ignoring this one injector because the others were fine and because it was impossible to get access to. Big mistake.

After removing upper and lower intakes, fuel rail, and testing the injectors, that particular injector had a reading that made no sense. The others were exact.

So I have no doubt it is bad. I have seen on Youtube how to actually apply voltage and make the spray, but I don't think I care enough about that right now. I'm going to put the new injector in and see how the truck does at this time.

I want to thank you and all others for the help and instruction you've provided. I will update soon after I get everything back together.
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Old 12-14-2017, 10:55 AM   #17
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Final post. I have reinstalled everything back. I test drove the truck last night, and it drove great.

The worst thing about this whole situation was that fuel injectors are expensive. I thought I would just replace one, but after inspecting the others, I had to change all of them. Although three of them tested within specs for resistance, they broken to pieces, literally. One had a disintegrated tip (that goes into the head port) and another had a broken plastic tip that goes into the fuel rail. They were all in really bad shape.

I have replaced all four. It was a super expensive fix for such an old truck, but at least it is running great.

The one piece of advice for anyone experiencing rough idle, and is following this thread, is to simply start unplugging stuff....spark plug wires, injectors, sensors...etc... If the engine doesn't change in RPM's, you know you're on to something.

I learned alot through this experience, specifically backprobing sensors with sewing t-pins and how better to diagnose rather than throwing parts at the truck.

I still threw a bunch of parts at it though because the bad fuel injector must have been slowly failing because sometimes the truck would run great, making me think that something I had done or replaced was a fix, when it wasn't. That was very frustrating.

One more note for anyone following - when installing all new injectors, don't be freak out if the injectors don't seem to line up perfectly in the fuel rail. I was getting very mad because it looked like the aftermarket injectors were too long or didn't fit right. But as soon as I gave up with how they looked, and tightened up the bolts on the fuel rail, it pulled the injectors into the fuel rail so they fit perfectly.

Thanks to everyone for all your advice, and unless something goes wrong with the truck that pertains to this particular thread, I am signing off.
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