Good Compression, but no idle...

[Joker's '88 GW]

I was searching thru the archives and found Alli's problem with the GW not wanting to idle, but running find when given gas.

I began to suspect that I may be a victim of the same type of problem. I pulled the valve cover off of the right side of the engine last night and other than the normal buildup of junk, it looked good. I pulled the 1 and 3 plugs and had my son turn the motor over and the compression felt good. (I don't have a compression gauge). That pretty much eliminated a broken piston or anything like that.

I am beginning to suspect the Intake Manifold Gasket... I'm getting oil and gas in my air breather and she won't idle. Have to do the 2 step (Left on Brake, Right on Gas) when coming to a stop... Not fun in traffic. She has been parked for the last week or so.

I'm working on getting a rebuild done, but in the meantime, does anyone in the Charlotte area have the time and experience to help me with changing the intake manifold gasket?

Thanks in advance....

[joe]

A first guess besides the obvious air leaks at/around/under carb etc would be a blown power valve in the carb?

[Stuka]

I would ask how often you have to add oil, but you obviously dont drive it tongue.gif

The intake on our rigs is easy to pull, you dont gota pull the distributer or anything. So it may be worth it to pull the intake and a new valley pan and front/rear seals on. Although this may not be your problem. The truck not wanting to idle, but seams to run fine when more throttle is applied sounds like a carb problem to me. Is black smoke comming out the tail pipe at idle? This would point out that its running way to rich at idle, and therefore loading up, and causeing it to stall. Have you checked your vacuum with a vacuum guage at all? Although this would be hard to do withhout it wanting to idle. Your carb may just need to be rebuilt. Rebuild kits are generally cheap for the 2150's. So you may want to look into that. Before I rebuilt my 4350 that I used to usse, my truck wouldent idle until it warmed up, because it loaded up so bad. After it warmed up, it would run ok. After I rebuilt it, it ran great. So, theres a few things to look at...hope I didnt confuse you to much smile.gif

[ChrisCollege]

Joe,

I am having the same problem with my 88GW. I thought the power valve would only effect the underload performance. Will it keep the truck from ideling well? I am asking because I know my power valve is bad.

[joe]

<BLOCKQUOTE>quote:</font><HR>Originally posted by ChrisCollege:
Joe,

I am having the same problem with my 88GW. I thought the power valve would only effect the underload performance. Will it keep the truck from ideling well? I am asking because I know my power valve is bad.<HR></BLOCKQUOTE>

Chris, hopefully someone will jump in here that's more in the know than I but I would think if the power valve can't hold enough vac to keep it closed it would leak added fuel into the carb even at idle and cause a rough idle?
If I'm way out here maybe someone can enlighten both of us ;)

[tito]

I had a similar problem, would idle real rough at a stop light, almost stall, but ran smooth when given gas. Sometimes there was a very slight hesitation/stumble at first. Gas mileage sucked too. Used to get an unbelievable 16.8mpg on the hwy. Once the "shakes" started I was lucky to get 11mpg. Turned out to be two vac hose leaks at one time. The first was the hose on the driver side base of the carb going to the EGR valve. It was cracked just past the "T" valve so it was hard to see. The other was hidden under/behind the distributor and plug wires on the front of the manifold. The heat had hardened the rubber and it must have vibrated off the connector. Fixed both leaks and it's back to running smooth with the bonus of good mileage again (15+mpg)/IMG] :eek: [/LIST]

Just some info in case it can save the time of tearing into the manifold.

[reddog]

Joker - how much gas and oil do you get in the air cleaner?? First thing to check with oil in the air cleaner in the PCV valve. I assume you have the 2150 Motocraft carb. Pull the vacuum hose off the bottom of the bowl at the front of the carb. If you have any fuel there the power valve is blown. Get a carb rebuild kit and rebuild the carb.

Chris and Joe - blown power valve usually creates a very rich condition and when the throttle is open enough air is fed in to lessen the effect of the problem. At idle with the throttle closed fuel is dumped creating a rough idle. Take a sniff of your exhaust pipe - if it smells like fuel check that power valve!! When my valve was blown black soot would drip out of the tailpipe.

Kerry

[nograin]

Basically a failed power valve in a Holley or Motocraft will do just what you said.

The power valve is a spring loaded diaphram that opens an addition fuel passage. When the manifold vacuum drops low enough, the valve opens the extra passage and more fuel can get pulled into the air fuel mix.

Soo, on one side is vacuum (attached externally on my '85) and the other side fuel. If the diaphram breaks in any way, extra fuel will be pulled into the intake through the vacuum lines. It will also get all into the vaccum lines and I suspect the CTO & NLVR valves are not happy living that way, nor are the vac hoses.

Pull the hose off the carb - it should be dry. Its in the front center of the 2150s and fairly low.

[Joker's '88 GW]

Now this is why I ask my questions here!!!

I have someone that is willing to rebuild the motor if it really needs it.

I'm going to check the power valve on the carb and see what it looks like.

For the last few days before I parked it, she would hard start after running, and blow black smoke out the exhaust. I could run on the highway fine, but around town, she wanted to die anytime I took my foot off of the throttle. I checked my PCV valve and you could see there was oil in it, but it operated fine. With knowing that the engine was needing a rebuild, I just parked it before I did more damage.

I will check the power valve and get back to the list...

this could be a much better deal that I originally thought..

Thanks for all the information..

tongue.gif

[EZ]

A problem I have seen often is dirt and or rust in main jets. that will not allow the metering rods to seat = no idle.

[Joker's '88 GW]

<BLOCKQUOTE>quote:</font><HR>Originally posted by nograin:
Pull the hose off the carb - it should be dry. Its in the front center of the 2150s and fairly low.<HR></BLOCKQUOTE>

Okay... I pulled all the hoses from the carb and they are all dry.

When everybody is talking about the power valve, is that the same as the accelerator pump on the front of the carb? It has a spring loaded diaphram in it. If that is a yes, then that looked fine also.

If anybody has any idea of what to look at next, I'm more than happy to check it and report back.

Thanks Everyone...

[Joker's '88 GW]

Okay... 1 more question...

On the passenger side of the carb are 2 tubes that enter the intake manifold. One is loose. these metal tubes go from the intake to the back area of the carb.

What are these tubes and does it matter that one is loose enough to move easily? I can't find mention of these in my Haynes manual.

Thanks...

[reddog]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Joker_87GW:
I'm going to check the power valve on the carb and see what it looks like.

For the last few days before I parked it, she would hard start after running, and blow black smoke out the exhaust. I could run on the highway fine, but around town, she wanted to die anytime I took my foot off of the throttle. tongue.gif<HR></BLOCKQUOTE>


The power valve MAY be dry if it has been sitting for a few weeks. Run the engine for a couple of minutes then check the power valve again. The symptoms you describe are classic blown power valve symptoms.

The power valve is below the accelerator pump on the bottom of the carb bowl. All you can do without pulling the carb off the intake is pull the vacuum hose off to check
for fuel leaking through the power valve.

The metal tube on the passinger side of the carb sounds like the one that feeds hot air to the choke. If it is loose that is ok.
Kerry

[ July 11, 2001: Message edited by: reddog ]

[ July 11, 2001: Message edited by: reddog ]

[Joker's '88 GW]

Okay... I guess I better get to pulling the carb... It can't hurt to pull it anyways..

Right now, she is out of gas and has the valve covers removed for inspection of the rockers and springs..

I may just begin pulling it apart to be able to see what I can find. Once I get the carb off, then I'll pull the intake and check the valley area.

During this time down, I'll sand and paint the valve covers.. pull the heads and check out the top end... I may just do a piece at a time until I get the rebuild arranged.

I figure, the more I take down, the easier it will be on the guy that does my rebuild...

It will be next week when I get to removing the carb.. Heading the the Highland Games tomorrow afternoon..

Scottish Games on Grandfather Mountain in Blowing Rock, North Carolina!!!

Gotta love Celtic Music!!

[nograin]

Lets see, I would think you have a 2150 like I do.

Accelerator pump faces forward and is mechanically actuated by the throttle linkage. Every time you move the throttle, a little gas should squirt into the barrels. You can see this by doing it when the engine is off and the air cleaner is removed.

Power valve is under the front bowl, and it is actuated by the manifold vacuum. That is it makes the mixture richer when the engine calls for it.

Black smoke is more likely rich mixture. Blue-gray is oil.

I'ld buy a thread in compression gage before going to a rebuild! So far I can't think of anything you've written that suggests engine problems..