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1995 K1500 Running Rough at Half Throttle


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MarineGrunt
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Sep 19, 2014, 4:26 AM

Post #1 of 28 (2018 views)
1995 K1500 Running Rough at Half Throttle Sign In

I haven't been around in awhile and hope everyone is doing well.


I have someone with a 1995 K1500 with the 5.7 with close to 200k on it. Here's the email I got from him.........
"It is a 95 GMC K1500 with the 5.7 (pre-Vortec) and almost 200,000 miles. The problem is with it running rough at part throttle, around 1200 rpm. Once you get through that at half throttle or more, it seems to be fine. I have given it a complete tune up, new fuel filter and new throttle body injectors with little to no change. I wonder about the catalytic converter because it is original. I would remove or replace it but is a single piece unit with the y pipe and y pipe bolts are completely rusted out. I would consider cutting off the converter and welding a different one on or just straight pipe but I don't have a welder capable of doing so."


I don't have the truck yet but will be getting it soon so didn't know if someone would have any ideas off of the top of their head or could point me in the right direction for troubleshooting so I can get started on it right away.


Thanks!


Hammer Time
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Sep 19, 2014, 4:40 AM

Post #2 of 28 (2012 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

Hey stranger..........
by the way you missed your football picks again.


I would take a hard look at the EGR system. Make sure it's not sticking open or leaking into the intake somewhere.

Have the codes read and see if there are any clues there.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Sep 19, 2014, 4:41 AM)


MarineGrunt
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Sep 19, 2014, 9:22 AM

Post #3 of 28 (1998 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

Thanks for the starting point HT. I appreciate it. I'm sure I'll have plenty more questions once he brings the truck over.
Yeah, not sure if you remember but we moved back in April. I was busy with work and busy getting settled in. Now it's time to get back to doing some work on vehicles. I really enjoy it and have missed it. The attached two stall garage is 24X30 and has a 12' ceiling so I finally have some decent space. I'd still like to build an building out back in the future. I'd love to have a lift.
I got on last night right before the game and did my picks. I remembered at like 6:47 central time. I had better check though. Maybe I didn't save them.


Hammer Time
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Sep 19, 2014, 11:35 AM

Post #4 of 28 (1996 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

Yep, you did save them. I hadn't been back since just before the game.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



kev2
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Sep 19, 2014, 12:06 PM

Post #5 of 28 (1992 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

this is a 1995 and you mention TBI - just the 2 injectors?

this is a easy to work system- BASICS.
fuel pressure - easier said than done BUT critical.
CODES - easy and quick- even if CEL is off.
Parts - AC Delco
For the cat concern- do you have a simple VACUUM gauge?


Tom Greenleaf
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Sep 20, 2014, 5:21 AM

Post #6 of 28 (1977 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

Hi MG! My 2 cents - Not converter yet if only part throttle issues but that's when EGR does it's work so suspect that or isn't getting properly controlled.


Vacuum gauge: If you don't have one get a pistol type with hose, gauge and assorted taps to monitor vacuum and it is also a vacuum pump for checking integrity of vacuum controlled items and diaphragms too.


An exhaust restriction from any cause while watching a vacuum gauge first at idle and again with no load at say 2,000 RPMs should be the same or real close. That is taken from manifold actual vacuum but "T" in so anything else it runs to gets the vacuum as you just observe,


T



Hammer Time
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Sep 20, 2014, 5:25 AM

Post #7 of 28 (1972 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

These symptoms do not indicate plugged exhaust.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Sep 20, 2014, 5:40 AM

Post #8 of 28 (1970 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

No they don't indicate an exhaust restriction. The pump and gauge mentioned can both watch and just show an item works at what vacuum like the EGR (system) highly suspect IMO,


T



MarineGrunt
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Sep 22, 2014, 10:16 PM

Post #9 of 28 (1944 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

The guy just dropped off the truck Monday evening so going to start messing with it in the morning. Sounds like the first thing I should do is test the egr valve. I'll let you know what I find.
Thanks for the help!


MarineGrunt
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Sep 23, 2014, 5:15 PM

Post #10 of 28 (1931 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

I hooked a vacuum pump up to the egr valve and it doesn't hold any pressure at all. That is the correct way to test it, right?


Discretesignals
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Sep 23, 2014, 5:25 PM

Post #11 of 28 (1930 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

pressure? Should hold vacuum unless it has a torn diaphram, your vacuum pump leaks, or it is one of those positive backpressure EGR valves.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


Hammer Time
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Sep 23, 2014, 5:32 PM

Post #12 of 28 (1927 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

Yes, some require exhaust backpressure before they will open.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



MarineGrunt
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Sep 23, 2014, 5:38 PM

Post #13 of 28 (1925 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

Hey DS...how have things been going?
I checked my pump and it's good to go. How do I know if it's a positive backpressure valves?





Discretesignals
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Sep 23, 2014, 5:38 PM

Post #14 of 28 (1925 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

If it a positive back pressure valve, you have to stuff a rag into the tail pipe to create some back pressure while applying vacuum to the valve. With the engine running of course...LOL.

Hanging in there buddy. Good to see your back around this joint.Wink





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Sep 23, 2014, 5:39 PM)


MarineGrunt
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Sep 23, 2014, 6:51 PM

Post #15 of 28 (1915 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

I'd have to replace every exhaust pipe in order to create back pressure. Any other ideas or a way to tell if it's a positive backpressure valve or not? I guess I could pull it off and test it by rigging a way to plug it.


(This post was edited by MarineGrunt on Sep 23, 2014, 6:53 PM)


MarineGrunt
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Sep 23, 2014, 7:45 PM

Post #16 of 28 (1910 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

You can see how I plugged it off in the picture below. I used a rubber cork in the opening with the plunger. My question here is, will that rubber cork prevent the plunger from moving thus not allowing the valve to close? If so, I figure I'll get a bigger rubber cork, hollow out the center, and put it on the outside.


The gauge instantly starts dropping, stops at 2 for about 3 seconds, and then drops to 0. It's doing the same thing when the egr valve is on the truck. I tested my vacuum pump and it seems to be working fine.

By the way, no codes were present or in the history. The battery looks brand new though so the history was probably wiped out when replaced.





(This post was edited by MarineGrunt on Sep 23, 2014, 8:19 PM)


Hammer Time
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Sep 24, 2014, 2:22 AM

Post #17 of 28 (1904 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

No, you can't test a feedback EGR that way. It has to be done with the engine running. The exhaust pressure triggers a valve inside the EGR that seals up the vacuum and allows it to be pulled open.

What we are looking for in your case is a valve that either isn't closing all the way or is opening too early when you're driving. If the pintle looks fully seated, put it back on the truck and try running the truck with the vacuum hose removed and plugged and see if the symptoms go away.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Sep 24, 2014, 2:32 AM

Post #18 of 28 (1902 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

Hmmm? Some funky. One vacuum hose goes to this EGR? With it off now you might be able to just pull on diaphragm while off and cool with vacuum line plugged while retracted or with vac pump and it should stay close to where it is not move the pintle any more with your rig (you are a hoot) off of it.


I've only had marginal luck cleaning a leaking pintle pressing it against wood with carb cleaner but those that can't shut should have a lousy idle not so much this mid throttle issue when it should be working. Idea of EGR is off at idle and off again at WOT. Little older on some people would plug the whole thing off thinking it would help for power and doesn't but can make engine knock instead as it's counting on some exhaust gas to flow back thru the thing to lower temp of combustion in turn reduces CO emissions and emissions in general but not harm performance,


T



MarineGrunt
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Sep 24, 2014, 3:52 AM

Post #19 of 28 (1897 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

Okay....I just assumed there was a flapper inside that closed once I put vacuum to it. So you're saying if I leave the vacuum hose unplugged, and symptoms go away, I know it's the culprit?
One other thing that might be worth mentioning is when you start the truck it cranks 5 or so times before it turns over. I had a few vehicles in the past where the fuel pressure regulator fixed an issue like that. I didn't know if maybe that would be worth looking it into after I'm done messing with the egr?


(This post was edited by MarineGrunt on Sep 24, 2014, 4:01 AM)


Hammer Time
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Sep 24, 2014, 5:33 AM

Post #20 of 28 (1891 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

That would prove the problem is in the EGR system, not necessarily the valve itself.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



kev2
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Sep 24, 2014, 9:03 AM

Post #21 of 28 (1885 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

install the valve.
be sure the pintel is seated.
with enging running remove the vacuum line from EGR valve follow it back to solenoid
is there VACUUM ? yes before solenoid (Sol to eng) no after solenoid. (sol to VAlve).

plug the vacuum line - drive vehicle - is it still having an isue?


MarineGrunt
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Sep 24, 2014, 10:48 AM

Post #22 of 28 (1879 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

There is vacuum before the solenoid and no vacuum after.
Going to plug the line and take it for a drive.


MarineGrunt
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Sep 24, 2014, 5:54 PM

Post #23 of 28 (1865 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

It runs fine with the egr unhooked. I'm thinking it's the egr and not the solenoid just because it does hold a vacuum, although barely at about 2 inches, for about 4 seconds. If it was a positive back pressure valve it wouldn't have a vacuum at all, correct? The line is getting vacuum on the engine side of the solenoid so I believe the lines are okay. Is there anything else besides the solenoid in the egr system? If the solenoid checks out, and the lines are okay, could it be anything else besides the valve?


Hammer Time
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Sep 24, 2014, 6:34 PM

Post #24 of 28 (1862 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

The solenoid is a possibility too. It isn't just on and off. It gets a series of pulses. The bottom line is the valve is opening too soon and likely too much. Could be either one or even the ECM programming. That car is probably using a PROM.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Sep 24, 2014, 6:35 PM)


kev2
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Sep 25, 2014, 11:04 AM

Post #25 of 28 (1846 views)
Re: 1995 K1500 Running Rough at Half Throttle Sign In

if you want to dive deeper into this - EGR disconnected - hook a vacuum gauge to the solenoid OUT and route the gauge so you can see as you drive- not as difficulrt as it sounds. BE AWARE that the windshield is there and its glass- as you drive observe the vacuum reading- should go to manifold @20" then return to 0 -

EGR seating is sometimes held OPEN by a piece of carbon.. ask a REAL parts store if there is a screened gasket for the EGR on this engine 5.7? If you replace the EGR do NOT get cheap avoid anything that comes with shims bushings...chevy wants the serial number to get correct one - yet advance has one that fits many engines wonder why?

with a mityvac- will the EGR valve open when vac applied or dump all vacuum as soon as it get pumped up? it should oen hold @30sec and bleed off






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