Is this an EGR/TVV problem?

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Nov 17, 2006 | 03:00 PM

randyredleg

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Melting Slicks

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From: Avon, Indiana

Is this an EGR/TVV problem?

I get a ping under load, but only after the engine has been up to operating temperature for some time. I don't think it's a timing issue.

Some reading suggests that this might be an EGR problem, although the EGR has less than 5000 miles on it. The vacuum to the EGR is controlled by a line to the TVV, which is influenced by temperature.

Is there an easy way to diagnose the EGR and the TVV? If the TVV needs to be replaced, is there a trick to removing it? It looks like a fragile piece of plastic. It seems to have a metal ring at the base, can you put a wrench on it?

Nov 18, 2006 | 09:45 PM

cmac72

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With the engine running, hook up a vacuum pump to the line going to he EGR valve and pull a vacuum to see what the engine does. Next, put a vacuum gauge on the line from the Vacuum control valve so see if it open up and pulls vacuum when he engine is at operating temperature. When the pinging starts, pull the line to the EGR valve and see if that stops it. When you insalled the EGR valve, did you have a choice as to the size opening to create (i.e., did you get a universal one that you had to add a certain sized washer to size the opening?) or did you get one specifically suited to the Vette? I ended up with a universal one that caused so many problems, I plated off the holes to it and installed it over the plate just for looks.

Nov 20, 2006 | 12:49 PM

Rich's'78

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From: Oakville ON

Quote:

Originally Posted by cmac72

With the engine running, hook up a vacuum pump to the line going to he EGR valve and pull a vacuum to see what the engine does.

I disagree - that will stall it out. The EGR valve should only see vacuum when the engine is under load. The TVS gets vacuum from a ported source on the carb so you don't have EGR until you are driving along.
With the engine hot, stop and run a piece of vac line from EGR to the carb port directly. Drive again - if the problem goes away it is either the TVS isn't opening (internally), the valve isn't working right, or you have a leaking vac line. Don't try taking the tubing off the TVS ports if you are not switching it out - when they are old the nipples break off really easily (even new!). They sell a special deep socket with a slot cut out to fit over the nipples for re + re. Two sizes. Mine is 1 1/8" I think.
Another posible cause for cruise pinging that is easy to overlook is the thermal switch/bimetallic slide inside the air cleaner housing (if you have it). I had a case where the thing was still blending in heated air under cruise - adjusted it's temperature activation to draw only outside air as it should when hot.

Nov 20, 2006 | 12:55 PM

cmac72

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I guess I must have been doing all wrong before. When I hooked up a vacuum gague to the Thermal value on a hot endine and reved the engine, I got vacuum. The old way of testing the EGR was to put a mirror where you could see the diaphram and rev the engine to see if it move inward. My pholosophy on vacuum hoses (all hoses, for that matter) is if they don't readily come off, put a slice in them and unwrap them from the fitting. I agree those nipples break off very easily. If the hose is that difficult to get off, the chances are it is probably ready to be replaced anyway. In any event, you can pull the vacuum line off the EGR valve w/o damage and attach a vacuum gague there.

Nov 20, 2006 | 06:27 PM

randyredleg

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From: Avon, Indiana

Thanks. I'll try this.
When I was playing with this the other day, if I pushed up on the hole under the EGR, the idle speed would increase. Same thing if I removed the vacuum line from the EGR-idle would increase.With cold engine and
the engine at idle should there not be any vacuum in the line to make a difference?

If it's the thermal switch, how do you adjust it?

Nov 20, 2006 | 08:52 PM

cmac72

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The switch can't be adjusted - it has to be replaced. I didn't go the route of the special socket (since I didn't even know one existed) - just used a plain ole open end wrench and prayed a lot. If I had known I could have bought another tool I would have been there!

Nov 21, 2006 | 12:24 PM

Rich's'78

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From: Oakville ON

The thermal switch is a bimetallic spring and the actuation temperature is set by a tiny Phillips screw inside the housing - it is adjustable, you have to cut open the housing to get at it (I later held the housing close with a piece of wire). You can play with the actuation temperature by turning the screw with the engine idling and seeing the door move. Before messing with it, look to see that the air cleaner door is fully open as soon as the engine is up to operating temperature - if it is, then it is not the problem.
I had one that was still pulling in heated air when the engine was hot and it pinged on the highway. Replaced the switch - same condition. After adjusting it, no problem.

Nov 21, 2006 | 12:44 PM

Rich's'78

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From: Oakville ON

Quote:

Originally Posted by randyredleg

I don't understand - "if I pushed up on the hole under the EGR, the idle speed would increase". If you are pushing the diaphragm up into the valve, that will allow EGR gas to flow and that should cause rough running, not an idle increase.
"With cold OR HOT engine and the engine at idle should there should not be any vacuum in the line " - correct if it is a simple valve. There is more than one design. A basic manual should confirm.