Truck wont idle - water in gas

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mazzov

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All,

I have a 2000 5.2 1500 ram, 4x4, 5 speed, stock. A week or so ago I got gas at a station that I typically don't go to. A few miles after getting the gas the truck performance took a dive. I was not able to get the truck to idle and it would just want to shut off. I was able to get it home thru some fancy footwork with the clutch. I dont have a receipt from the gas station so I really dont have any proof that I got gas from them (big mistake). Since then I have removed the bed and drained the tank dry, cleaned the filter screen at the base of the fuel pump module and put in fresh gas along with some dry gas chemical. Prior to draining I did siphon out water from the tank.

Currently the truck will start fine and run good for about 2 minutes after that the idle will vary between 1000 and 600 rpm till it stalls out. I have already ruled out possible catalytic problems by removing the catalytic and having the same results. I have also ruled out the plenum by not smelling gas thru the oil dipstick. I was able to swap the map sensor with one from a buddies truck (2001 same style) and there was no change. I removed the IAC and cleaned it and there was also no change. I have not touched the TPS as of yet. I have also tested the battery and alternator and they are fine. I suspect that the pump may be on its way out but I am not able to measure the fuel pressure due to not having a guage. If I was to push the schrader valve on the fuel rail while the truck is at idle should fuel "shoot" out or "drip" out - would this be a good indication that the pump is shot?

The truck did run fine prior to getting the new (bad) gas.

Any suggestions are appreciated.

thx.

mazzov
 

dapepper9

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Might try a bottle of seafoam with a couple gallons of the fresh gas. Seafoam is a pretty good option if there's still some water in pump, lines,and injectors
 

R.L.K.

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Seafoam is a good idea , you may try and just replace the IAC , make sure you use the OEM one though , cheep Chinese & aftermarket ones seem to give folks issues .
 

dudeman2009

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Water is more dense than gasoline, however fuel pumps are designed to stir up enough around the pickup screen that when coupled with vehicle movement will ensure that straight water doesn't get sucked in; so long as its not half water half gas, or something ridiculous like that.

I would first try bleeding the system. There are a couple ways to go about this. Seafoam has been mentioned as is good at getting things out of the fuel delivery system. Water has a higher surface tension than gasoline, so it may not pass as well as gasoline through small spaces like injectors. Seafoam will help clean the injectors of all buildup. Another option is to have someone cycle the key in order to prime the fuel pump while you depress the schrader valve and capture the released fuel with a rag or something that will keep the mess down. If fuel gets all over, just let it evaporate for a few minutes. Check to see if it will idle on its own from time to time.

Another possibility is the PCM has learned to run on watered down gasoline and is now unable to run well on straight gas. Disconnecting the battery and letting it sit for 10 minutes switching the key a couple times will clear its memory and restore factory default numbers. After reconnecting the battery if it doesn't start on the first try, give it a little gas while cranking. Sometimes these engines have trouble starting after having the PCM cleared, it will take aprox. 2 minutes of driver assisted idle for the PCM to relearn timing and fuel trims.

Short of having a fuel pressure tester, poking the bleeder valve on the fuel rail will not indicate line pressure unless there is none. There are too many factors that play into how much fuel is ejected, such as the amount of depression of the valve or size of the object being used to depress it.

If you have a scan tool you can check the fuel trims while its running. Positive numbers indicate the PCM is adding fuel to bring it to balance, negative numbers indicate the PCM is removing fuel to bring it to a balance.

If you dont have a scantool you might want to see if an autoshop nearby will let you use one for free or rent either a scantool or fuel pressure tester to you.

Otherwise you are going to be guessing as to whether the fuel pump is bad or not. A little bit of water intake should not hurt the fuel pump much at all.
 
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mazzov

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Thank you all,

Tonight I think I can rule out the IAC - I had disconnect it tonight (electrically) and it ran really bad. I also disconnected the PVC and there was plenty of vacuum from the plenum. I also looked inside the plenum and did not notice any puddles of oil - everything looked pretty clean.

I forgot to mention that I do have a code P0108 MAP Pressure Circuit High Input. I don't know how to test for this other than swapping it with another which I had done with no change in performance.

I did however just try the disconnect and wait 10 minutes for PCM to rest trick (thx dudeman2009) and was kinda surprised that I was able to get the truck running. It ran ok for the first minute or so then went into the high/low rpm but never stalled out. It sounded like it was starving for air or fuel. All the noise was coming from the throttle body. I tried to post a video but had no success.

When I was playing with it tonight during the high/low idle (800 -500rpm) if I was to bring the idle up to 2000 to 2500 rpm it would stall out.

Also should I suspect the charcoal canisters that are mounted on the frame? Starting to lean toward the pump. Also I measured the battery voltage was 12.5 and the alternator was 13.9.

Thanks all for the help.
 
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mazzov

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All,

Just an update. I have swapped all the parts (IAC, MAP and TPS) with parts from a friends truck of the same year and I still have the same problem. I am going crazy trying to figure out the problem. I had tested the fuel pressure at the idle (prior to it surging) and I had 49 psi. I did think of testing it during the surge (duh on me). I am really at wits end on this thing. The only thing that has not been done is changing the fuel pump. Perhaps the regulator is having an issue? IDK

After swapping out the MAP sensor I still had the P0108 code. And I did disconnect the negative each time I made changes.
 

Yeret

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Got any vacuum leaks? After some brief reading, it sounds like the signal voltage from the MAP sensor is too high for the operating condition of the engine.

At idle, the engine vacuum is strong and the MAP sensor sends a low signal voltage to the ECU. The ECU interprets this, as well as "zero" input from the TPS as the engine running at idle.

As throttle input increases, engine vacuum begins to weaken as the pressure between the manifold and the atmosphere equalizes. The MAP sensor's signal voltage increases as well and the computer interprets this, as well as increased input from the TPS as the engine under load and will adjust the injector pulse accordingly.

Now what you seem to have going on is the MAP sensor is sending a high signal voltage despite the fact that the engine is idling. Going by this, the computer thinks that the engine is under load, however when the computer compares the MAP's signal to the TPS's signal, it detects a conflict. In other words, the MAP is reading like the engine is under load while the TPS is reading like the engine is idling. As a result, the computer can't adjust injector pulse properly and will result in engine running issues.

The question of course is why is the MAP sending such a high signal voltage? There are, unfortunately, a lot of things than cause this. You've mentioned that you swapped a different MAP sensor but are still having problems. It's possible, though not probable, that both you and your friend's MAP sensors are bad but I wouldn't suspect the sensor itself. You also made mention of a wavering idle (500-800 RPM). Vaccuum leaks just loooove to screw with your idle, which does help make their presence known. Regarding the MAP sensor, a strong enough vaccuum leak could cause the sensor to act as if the engine is under heavy throttle even when it's just sitting at idle. As the engine throttles up, the signal voltage just continues to rise inappropriately especially in relation to the TPS until it reaches maximum. The ECU can't deal with this "conflict."

Bottom line is as long as the ECU is receiving a wonky signal from the MAP, it can't adjust injector pulse appropriately and the engine is going to have running issues, if it even runs at all.

Find out what's screwing with the MAP's signal voltage and I wager that you'll resolve your running issues. This is all just my personal theory so don't lynch me if I'm wrong, LOL.
 
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