5.3 runs very rough under load

[Craig C]

2002 Tahoe 210,000 miles. Engine starts right up and idles smooth in park. In park engine revs freely with no hesitation or noise. In drive the engine is smooth if you keep the throttle low enough to keep RPMs under about 1800-2000. Give it any more throttle and the engine vibrates, has no power, and pings badly. To get to 60 mph on flat ground takes about half a mile or longer of light throttle. Drives along fairly smoothly in overdrive at around 55-60 mpg and 1800 rpm.

The only engine code is for a MAF sensor which I have replaced, and the usual gas cap code.

Any ideas?

 

[Kraig]

I'm going to guess pluggd cats.

 

[ccapehartusarmyINF.(ret)]

pull one of your spark plugs and see what they look like
maybe knock sensors or pre cat 02 sensors or like he said clogged cats

 

[VikingTrad3r]

what are the fuel trims doing? if u have an iPhone or an android phone you can get an EL M3 to seven and figure out what you feel trims are doing for about 35 bucks. Once you find out what your fuel trims are doing you will be able to deduce exactly what the problem is

elm327

i connect it to my laptop

 

[VikingTrad3r]

you can test for blocked catalytic converter's by going to your local cheap hardware store and buying a temperature gun laser thingy. Take the temperature right before the catalytic converter and take the temperature after the catalytic converter if your catalytic converter is plugged it will be much hotter on the upstream side of the converter because the exhaust basically stops flowing afterwards. Personally I doubt that's the issue.

but for $15 check it and report back

 

[Craig C]

Thanks for the feedback. Soon as it warms up a little I will get out and give them a look see.

 

[Craig C]

So I finally got decent weather to test some things out. The codes it has are for P0178 Flex fuel sensor and P0441 incorrect purge flow. According to autozone's whizbang computer troubleshooter that points to a bad fuel tank preassure sensor. Not an expensive part but Im not yet sure I have enough clearance with the tools I have to get the tank down and out to check/replace. Weird troubleshooting process cause I was first puzzled by the P0178 cause there is no indication that this is a flex fuel engine anywhere.

 

[VikingTrad3r]

Good work so far craig. have you driven under load to recreate the stumble and seen a fuel pressure drop? typically i tape the fuel pressure gauge to the window and go for a drive.

So I finally got decent weather to test some things out. The codes it has are for P0178 Flex fuel sensor and P0441 incorrect purge flow. According to autozone's whizbang computer troubleshooter that points to a bad fuel tank preassure sensor. Not an expensive part but Im not yet sure I have enough clearance with the tools I have to get the tank down and out to check/replace. Weird troubleshooting process cause I was first puzzled by the P0178 cause there is no indication that this is a flex fuel engine anywhere.

 

[Craig C]

Going to track down gauge tomorrow, didnt find one in our little town today. In reading about both of the error codes everything I have said so far that neither sensor should have much of an effect on drivability, but maybe both together I guess. Had forgotten how long since fuel filter had been changed but it was about 12k miles ago.

 

[Craig C]

So had some other things to do and had the battery unhooked for a couple hours. When I hooked it back up the only code I have now is the P0440 (gas cap) code. The truck is running a little better, I would say about 25% better. I can accelerate slightly faster than I have been able to before. I had also cleaned the connector on the flex fuel sensor.
Maybe can get a ride somewhere tomorrow that will have fuel preassure gauge.

 

[Craig C]

after terrorizing the neighbors by unhooking the exhaust it proved to be both cats plugged big time. After a a morning in the exhaust shop its back to running like a champ.

Thanks to all those with their advise.

 

[VikingTrad3r]

after terrorizing the neighbors by unhooking the exhaust it proved to be both cats plugged big time. After a a morning in the exhaust shop its back to running like a champ.

Thanks to all those with their advise.

nice work craig. did u ever try the temp before and after the cats? ive read that is the way to test for a plugged cat but never done it myself.

 

[treehan77]

How much were new cats? You had the shop do all work?

 

[Craig C]

400 parts and labor. since they were welded in I didnt attempt it. Didnt want to try to cut out and piece it back together.

 

[treehan77]

400 parts and labor. since they were welded in I didnt attempt it. Didnt want to try to cut out and piece it back together.

Good to know, doesn't sound too awful bad to get it back in shape

 

[electro]

Why did you have plugged cats?

 

[VikingTrad3r]

Why did you have plugged cats?

fuel trims will tell...

 

[SLCHOE]

Why did you have plugged cats?

fuel trims will tell...

Yep. Now that you've spent the money on the cats it's time to find out what caused them to deteriorate. Sounds like you have a vacuum leak and the PCM is compensating by adding fuel (high fuel trims) to get the a/f ratio to stoichiometric ratio (14.7 parts air to 1 part fuel). Excessively high fuel trims will kill your new cats in no time flat especially with them being weld-in universals. Find the root of the problem and fix that too. You're not done yet.

 

[VikingTrad3r]

Yep. Now that you've spent the money on the cats it's time to find out what caused them to deteriorate. Sounds like you have a vacuum leak and the PCM is compensating by adding fuel (high fuel trims) to get the a/f ratio to stoichiometric ratio (14.7 parts air to 1 part fuel). Excessively high fuel trims will kill your new cats in no time flat especially with them being weld-in universals. Find the root of the problem and fix that too. You're not done yet.

^^^. he is right.

if you have a laptop, all u need is an elm327 and u can scan your fuel ttims.

OR. what type of phone do you use and I can maybe make a recommendation that's even easier then a laptop

 

[VikingTrad3r]

well, i was under my denlfali xl today after i had been running it for 20 minutes. my driver side cat appears to be on its way out because the exhaust was completely cold behind the cat. the other side was nice and warm.

ill hook up a scanner and see what the numbersbehind the cat.