Does my 1996 GMC Jimmy need a valve job??

Hi everyone! I have a 6 cylinder, 2WD, 1996 GMC Jimmy. I'm the original owner and have faithfully changed the oil, and all filters, at 3,000 mile intervals.
My Jimmy has the original engine and automatic transmission. I have just reached 345,000 and I've been told that I need a "valve job" due to a ack of compression in two valves.
When I took my car to my mechanic I was sure that he was going to say that it was a transmission issue. Let me explain: yesterday when I was driving up a small grade it felt as if I was towing a trailer. My engine revved up but felt as if it wasn't changing gears. It strained to go from 1st gear to a higher gear. I normally drive on 'overdrive' and it's always shifted smoothly. So, my immediate thought was a transmission problem. I know about the 'limping' setting that can occur with GMC trannies and I thought for sure that when my mechanic checked for the code that the transmission issue would show itself. Oh, I was able to drive it for the rest of the day without the 'problem' recurring.
So here's the question....does this sound like a 'valve' issue? He told me that I need to have a 'valve' job. He sad that the compression was bad. I've always trusted him, he's worked on my car for many years but given the $1,600+ cost I'm trying to do the right thing. I've planned on keeping my Jimmy for several more years. How can I be sure that I need a 'valve job'.
Thank you for your opinions and expertise....it is greatly appreciated!
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Louise wrote:

--
Steve W.

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Louise wrote:

Is it possible that after that many miles you have a couple valves that need attention? Yes. BUT from your description it doesn't sound like valves, it sounds more like a trans problem. Not all trans problems will set codes, especially in a 96 as it has very limited computer control of the trans.
Reasoning is : You say that you started up a small grade and it started to rev up but not go faster, that sounds a lot like a slipping clutch pack. Either due to lack of service, low fluid or just wearing out.
You then state that this problem didn't occur again. An engine valve problem that is noticeable will not suddenly repair itself, it can only get worse.
Pull the stick on the trans and look and small the fluid. It should be a nice red color and small like oil. If it is a dirty red or brown tinted and smalls like burnt oil, you have a trans problem. A fluid and filter change would be a place to start, if that's the case.
--
Steve W.

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replying to Steve W. , Louise wrote:

Hi Steve W...
Thank you for your response. After I posted my question here I called my local GMC dealer and shared my experience with them. Much to my delight, they were VERY helpful. They said exactly the same thing that you did!
Contrary to my independent mechanics original diagnosis my mechanic recanted and told me that after driving my car for about 15 minutes that he felt it was NOT a valve issue. He checked the transmission fluid level and found that it was dangerously low, almost empty. Needless to say, he apologized profusely, not only for the incorrect diagnosis, but also because he has been maintaining my Jimmy for years and has ignored checking the trans fluid level.
I've learned one thing from this experience -- I will aways check my fluid levels myself!
Thank you for the tips, Steve. I will definitely keep an eye on ALL the fluids in my Jimmy, not just the oil and coolant levels. I hope to get 500,000 miles out of the car with as many original parts as possible. Maybe at that point GM will find it in their heart to 'donate' a new Yukon to this GM fan! Hahaha -- a girl can dream!
Once again, thank you Steve. I appreciate the time that you took to explain everything to me. This site is awesome.
Best Wishes ~
Louise in California
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Louise wrote:

No problem. Glad to hear it wasn't as bad as it could have been. Being a 96 there are a few things I suggest though to make it last longer.
Have a "top cylinder cleaning" done. This cleans carbon out of the EGR passages and the cylinders. Helps keep the engine happy and avoid the EGR flow codes a bit.
If they haven't been changed have the intake manifold gaskets changed. They are a known problem on the 4.3. They fail and leak into the engine. Coolant in the oil doesn't work so well.
If this is a 4X4 (could be ordered as a 2 wheel drive) remove the battery, then unbolt the battery tray. Under it you will find the 4X4 axle actuator. wipe it off real well, spray some silicone on a rag and wipe the rubber down. Coat the cable connection on the bellows with a bit of either silicone grease or a bit of paint.
Clean and paint the battery tray, find a thin section of rubber (I use a chunk of old inner tube), cut the rubber to fit inside the tray snug. Then put the battery back in after wiping it down. The reason for this is that the battery gases as it charges and heats up. The acidic gas likes to settle and eats the battery tray, it also draws moisture and drips onto the actuator. Then they fail.
The 4X4 vacuum interlock valve on the transfer case likes to bind and fail. They are currently cheap but who knows how long they will be a common shelf item. I have a couple hanging in the shop just in case.
Most of these are not rush items. They are simply OOPs that can be corrected.
The exception being the intake gaskets. Don't use the factory ones. FelPro makes an updated one with a metal core to replace the factory plastic ones.
If you want to see what and why: http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/coolant-leaking-from-intake-manifold-gaskets
--
Steve W.

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wrote:

I agree with your reasoning.
Next step though, is how much do you want to invest in this vehicle?
It may need a valve job, but with that many miles, rings and bearings are probably worn near their maximum. Do you want to pull the heads for a valve job, put them back only to find a month later you have to pull them to do more internal work?
Rebuild the trans to find the engine is going bad? Or vise versa. If you live in a dry place and the body is in great shape, it may be well worth the money. If it is showing rust, worn chassis parts, it may be time to look at new(er).
I can se where you'd invest $4000 to $7000 in the drivetrain to have the body fall apart.
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replying to Ed Pawlowski , Louise wrote:

Hi Ed! You brought up some very valid points, and definitely things that I should consider before spending a large amount of money on my Jimmy. I just picked up my car from my mechanic this morning and it's running smoothly. The auto trans is shifting as it should, and the engine appears to be running fine.
I do feel very lucky to have a car that is pushing 350,000 miles that still has the original engine and transmission. It is a southern California car that has never seen a flood, or salt on the road, so the body is in immaculate condition. And you're right, if I had issues with the body, or even the interior, I wouldn't be putting a penny into it -- it would be at the GMC graveyard. But, since I've owned it since it was new - and know it's complete history - I don't mind putting a little money into its upkeep.
Thanks for the insight. You've given me some things to think about!
Have an awesome day ~
Louise
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On 3/21/2014 6:18 PM, Louise wrote:

In that case, keep on truck'n and shoot for 500,000 miles. Glad to hear it is still going!
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Louise wrote:

I wish my poor 02 had a nice clean body. NY eats them like candy... Mines been driven through 4 floods, salt, dirt, brush, snow.. Still looks good for an 02 but it's showing some spots.
Thing that stinks is that it's the ideal vehicle size and capabilities for what I use it for. GM had to stop making them and the replacements just don't quite make it for me. So I've been hunting for a southern version. Figure I could strip it down, treat all the rust prone spots and spay it with Waxoyl in all the pockets. Put Ni-Copp lines on it and correct some of the design flaws to make a better version.
--
Steve W.

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replying to Steve W. , Louise wrote:

Yeah, I guess living in California has offered me the ability to maintain the exterior, as well as the engine, without too much effort. When I was just a little girl my father taught me to take care of his car...so now, whether I'm waxing mine - or just checking the air in the tires - I will always remember the special times I spent with my father washing his cars and learning from him. He's been gone for a few years now, but my love of cars lives on in his memory.
Good luck with your '02, Steve! I know it must be a challenge maintaining your car in the New York winters -- but it sounds as if you have the resolve to get the job done.
Happy Springtime! I hope you, and your car, enjoy the warmer days to come....
Louise 🚙
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