Help with another diagnosis?

[bohmankid]

Vehicle in question: 1985 gmc 2500 with 2001 5.3 vortec motor.
My truck is running crappy. When I floor it (or even go past half throttle) the truck bogs down and will not accelerate. If I accelerate slowly, it'll go.. just slowly.. When it's in park, I'll put the pedal to the metal and it will cut out at 3-4000 RPMS. (Sounds like a rev limiter at 3500 RPMS). I've tested the fuel pump and all fuel lines are fine. The check engine light never comes on. Spark plugs are brand new (started having these symptoms with old plugs, so it's not plugs). Suggestions?
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[ls1nova71]

What's your fuel pressure?

[85burb]

any aftermarket stuff? Cam, headers. My burb did that but i have a cam and headers and i had it tuned and the issues all went away and has tons more power.

[BR3W CITY]

Scan the ecm even if the engine light isn't coming on, see if there are any stored codes. I have had an ecm code without the light really staying on; certain codes will cause it to pop up but may be shut off shortly after (sometimes evap codes will do that if they haven't been removed).

Clogged fuel injector, problem with the maf, maybe the tps, there are a few ways it could go. More info always helps.

[bohmankid]

Thanks for replies.
My first thought was a fuel issue as well. But the pump, braided lines, and filter are all brand new.
I'm using the stock regulator on the lines attached to the manifold. I'll check the vacuum, is there a way to adjust it? Maybe one of my injectors are clogged, what's a good way to test those? (I really need a gage lol. I don't have one)
And as for the exhaust, there are no cats and O2's are brand new. It's just long tubes - pipe - muffler - tailpipe so there are no restrictions there.
I also thought a coil could be bad? Or some sort of sensor. I'll scan the ECM to check for stored codes.
Also, the motor is stock. I do have a few bolt ons and am running a stock tune with stuff like emissions deleted. But it ran great for a few months. Even took it to the drag strip with no problems.
ONE MORE THING. The transmission is shifting funny. It will shift hard at high RPMS and it doesn't feel right. Could the whole problem be the tranny? It's a th400.
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[BR3W CITY]

Long tubes and a free flowing exhaust is enough to effect the feel of the vehicle a bit, though by itself wouldn't cause all your symptoms.

Tranny situation definately doesn't help things, but it also doesn't explain why revving in neutral has problems.

If a coil was bad you would probably get a misfire code, but you can always pull the plug but leave the wire attached and try cranking it with the fuel pump fuse pulled to check for spark.

How is your MAF positioned, and did you put a cone filter in? If you put in a cone filter like a K&N, its possible you used too much filter oil or did not let it dry, and coated the MAF or IAT with filter oil and it's causing issues.

[clinebarger]

Originally Posted by bohmankid

I really need a gage lol. I don't have onePosted via Mobile Device

R-12 gauges work really good for this. A old Robin-Air set can be had cheap.

[66C06]

One of 2 things here....

1. Unplug your MAF sensor and see if it runs better. If it does then you need to look at the o2's or getting a dyno tune. Since you are running no cats you might need to have a tuner turn off the rear o2's in the computer.

2. Check your TPS. Many times they go bad and can cause all kinds of sputtering and delayed throttle response,etc.

Just saw you post about you transmission. We had a similar issue with a 6.0 swap. Albeit was a 4l60e, the tuner had the shift points wrong in the tune and it caused some of the same issues. Eventually it burnt the trans mission up to where it would shift right and would only go to about 4k rpms, or you would give it gas and the truck would die. A re-tune and trans rebuild fixed the problem. Hopefully thats not your issue.

[BR3W CITY]

If he's running a th400 it can't be his issue, since the tune doesn't affect anything it does.
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[bohmankid]

Originally Posted by BR3W CITY

If a coil was bad you would probably get a misfire code, but you can always pull the plug but leave the wire attached and try cranking it with the fuel pump fuse pulled to check for spark.

How is your MAF positioned, and did you put a cone filter in? If you put in a cone filter like a K&N, its possible you used too much filter oil or did not let it dry, and coated the MAF or IAT with filter oil and it's causing issues.

Yeah, I'll have to troubleshoot when I get some time. Work takes up most of my hobby time now-a-days
The filter is a cone but it one of those cheaper 'oil-less' filters. The truck has the same symptoms with the filter off.

Originally Posted by clinebarger

R-12 gauges work really good for this. A old Robin-Air set can be had cheap.

Thanks for the tip!

Originally Posted by 66C06

One of 2 things here....

1. Unplug your MAF sensor and see if it runs better. If it does then you need to look at the o2's or getting a dyno tune. Since you are running no cats you might need to have a tuner turn off the rear o2's in the computer.

2. Check your TPS. Many times they go bad and can cause all kinds of sputtering and delayed throttle response,etc.

The rear O2's have been tuned out already. along with all the other emission stuff. trans stuff has also been tuned out since I'm using the non-electonic th400.

I'm trying and find time to look at it. I actually drove the truck to work today, so that shows you how HUGE of a problem this is. It feels like it runs great as long as I keep it under 1/4 throttle. Anything more than 1/4 throttle and it bogs and feels like it's missing but not sure.

A friend hooked me up with a tps and fuel rail with regulator and injectors to test out/troubleshoot. I'll also check my fuel filter. It's a brand new tank and everything as well so I wouldn't have thought about clogged lines.
I'll also plug it in to a scanner. the battery was unplugged recently for an extended time, so there could be saved codes in there right? I think the MIL light is working fine, it turns on when I turn the key to on position.
I'll do some troubleshooting, I'm willing to bet it's something simple that'll make me look like a doofus

[OKGMC4]

Mine did the same thing... 01' 5.3, stumbled and ran bad, no power. Found a bad regulator. Pull the vacuum line on the fuel reg. while it's running, if gas comes out of it, it is bad. Replaced mine and ran much better. Hope you figure it out soon whether that's it or not. Good luck.

[bohmankid]

All right here's an update. Too bad it's in the wrong direction..
The truck broke down as i left work today. The truck won't start at all now. Has crank, no start. It's acting like it's not getting gas. I towed it home and will troubleshoot tomorrow. Thanks for the replies.
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[ls1nova71]

Do you have an in tank pump? If so, the hose between the pump and sender may have come apart, either blew off, or blew a hole in it. You need to put a gauge on it. Can you hear the pump running?
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[bohmankid]

Originally Posted by ls1nova71

Do you have an in tank pump? If so, the hose between the pump and sender may have come apart, either blew off, or blew a hole in it. You need to put a gauge on it. Can you hear the pump running?
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I thought that as well. I pulled it out and all looks great. Pump is running, and all lines look normal. Hooking a gage up is on my to do list, I'll keep updating.
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[BR3W CITY]

Are u getting an honest 12+v at the pump?

Do the symptoms change dependingon how full the gas tank is.
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[bohmankid]

Problem fixed. A friend of mine gave me an extra fuel rail with injectors plus a regulator, and a TPS sensor to try out. The truck now runs great so the problem was either the injectors, TPS, or regulator... I'll clean my injectors and throw them back on and see how she does. I'll probly replace the regulator as well cuz the old one I pulled off was extremely dirty.
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