EGR valve - hillbilly fix

[Ripsaw]

Hi guys,
Back again with problems on the wife's 91 silverado PU with the 305 that I fixed last year. Of course when i replaced every single thing under the hood, I didn't replace the EGR valve. Found the testing procedures and performed them, and the valve is failing to seat off and is sucking air from vacuum test at the valve.

So my question is this.

Has anyone ever tried to use Hopps bore solvent for gun cleaning and an eyedropper to apply it to the shaft of the valve, let it run down and penetrate in there, and work the valve open and closed to clean it off to make it seat closed ?

Is there a seat like a valve in there that matches the shaft ?

Do you think this may help or will it harm something else in there ?

It is after all, used for removing carbon residue in guns.

Comments and opinions needed and welcomed. That's right, always short on cash and need another way to fix it if possible....Thanks for any help...Rip

[ChevyTech]

There is a very good chance that vehicle has a negative back-pressure EGR valve on it, which has more to it then people realize.

Here is a site with a good illustration of a negative back-pressure EGR valve.
http://shbox.com/1/EGR_valve.jpg

I have seen people bead blast them with spark plug cleaning machines. ( I would only do this to a port EGR vale)
I have used carburetor cleaner on them.
I have scrapped picked and dug at them with screwdrivers and picks.
I have used chemical carbon stripper on them.

I don't see any problem with using various chemicals to clean the plunger area as long as you keep them out of the diaphragm.

You can search EGR and my username to find many posts on EGR.

[67 Burb]

On my 95 Silverado, the EGR valve wasn't seating. I soaked it in carb cleaner and blew it out, soaked again and blew some more. Did this about 4or 5 times and the valve finally seated. Saved me some bucks.

As long as the diaphragm is not leaking, it's worth a try to clean it out.

[Ripsaw]

Yep, mine is negative pressure as evidenced by the N on the part number on it.

Thanks guys, yeah I saw that illustration on your sticky thread from researching before posting.

I was wondering though, exactly what pressure they are referring too ?

I assumed it meant one seat is on the bottom side of the valve stem flat, and the other type is on the top side, so the spring is either influencing it one direction or the other correct ?

Negative or positive pressure from the spring ?

[ChevyTech]

Originally Posted by Ripsaw

Yep, mine is negative pressure as evidenced by the N on the part number on it...

... I was wondering though, exactly what pressure they are referring too ?

The pressure in the exhaust system, is the pressure they are referring to.

With Negative back-pressure valves, the slightest pulse of pressure in the exhaust system will modulate recirculation (close the valve at least some).

[Ripsaw]

Thanks Chevy Tech.

Then I suppose if a catalytic converter were clogged it would cause the EGR to act goofy too ?

I smelled huge amounts of fuel out of the exhaust when this started happening and running like crap. Another odd thing is the radiator developed a leak around the same time, so I started thinking head gasket or pressure in the radiator.

Maybe not even related but did see some white floating stuff in the radiator when I pulled the cap to check water level after filling the plastic tank on the firewall.

I guess it's time for a compression check of the cylinders too ?

[ChevyTech]

Originally Posted by Ripsaw

Thanks Chevy Tech.

You're welcome!

Originally Posted by Ripsaw

Then I suppose if a catalytic converter were clogged it would cause the EGR to act goofy too ?

Yes.

Originally Posted by Ripsaw

I smelled huge amounts of fuel out of the exhaust when this started happening and running like crap.

Test the coolant sensor that the ECM monitors. It controls the mixture that gets injected.
Test information can be found here:
http://67-72chevytrucks.com/vboard/s...25&postcount=7

Originally Posted by Ripsaw

Another odd thing is the radiator developed a leak around the same time, so I started thinking head gasket or pressure in the radiator.

Maybe not even related but did see some white floating stuff in the radiator when I pulled the cap to check water level after filling the plastic tank on the firewall.

I guess it's time for a compression check of the cylinders too ?

Head gasket failure is common on these trucks. If the coolant sensor is ok then testing compression may be a good idea.

[c10sport]

I was having problems with pinging and the SES light showing an EGR code. Thankfully, I found a new GM EGR (new as in just replaced before being junked) at the junkyard.

[Ripsaw]

Tested coolant sensor and ground and replaced the EGR valve, still doing the same thing, erratic idle and tach surges up and down. Guess it's time to go replace the ECM to see if it's any good, have a spare from when I did my truck and replaced entire distributor on the 89'. Solenoid checked out fine as did the wires and circuit at the solenoid. 12 volts with key on.... and ohm's out across it.

If the ECM has no effect, looks like I go to compression testing. It's really odd though, because when it starts to warm a little, it gets worse and acts like it is flooding or getting too much fuel, then dies if I don't nurse it along with the accelerator to keep it running. Fuel pressure is fine at 12lbs. Then when it gets a little hotter sitting and running, and I try to nurse it to keep it going, it dies. Will restart but runs crappy.

Any more ideas ? If not, I will assume I am on the right track of how to proceed, thanks again guys.

[ChevyTech]

It is very unlikely that the problem is the ECM.

When is acts up, unplug the oxygen sensor to force it back into open loop operation, and see how it runs.

Do you have exhaust leaks anywhere near the front of the truck?
Have you ever replaced the oxygen sensor?

[Ripsaw]

Yes Tech, I replaced it and the one at the exhaust on driver side when I got a code previously while doing the timing chain last Christmas. IIRC it was a 43 code.

I replaced the ECM with no change and tested the coolant sensor and it showed 100 on the multimeter green scale, but scales reads that the green is x 1000, so kinda confused yet. If it is supposed to be 177 could it be the culprit ? it is relatively new with only 1000 miles on it since I changed it and swapped ground location as you suggested last holiday season.

It was not up to temp. if that matters when checked. Cold before starting is when I unplugged it and checked it.

No exhaust leaks anywhere.

If I unplug the oxygen sensor and it runs better, what does that mean ?
A Bad sensor ?

When I just did all that last time, I replaced the IAC valve and TPS at same time. It ran perfect after timing chain and we fixed all that other stuff with timing you helped me on. Hard to believe the coolant sensor and oxygen sensor may be going bad already, but not surprised with the way things are made so cheap these days. Lots of fuel smell though when it started messing up.

I ran it all the way to Galveston from Hattiesburg and back at 70mph without a problem, ....perfection and got 22.3 miles per gallon. Couldn't have done it without you either. Was able to see my Mom before she went down too bad. Thanks for last year !

Will unplug O2 sensor tomorrow and let you know my friend.....best regards, rip.

P.S.
One last thing, the replacement EGR was positive pressure and they allowed it will work with right orifice washer, part was right according to cross reference to original negative pressure valve, and no OEM part available here. I used #42 washer and staked it in as per instructions, I guess it will work, they said money back if it don't....no more codes while running at any rate ???.....just still running crappy.

[ChevyTech]

Sorry to hear about your mom!

When checking the coolant sensor you need to know what the coolant temperature is.

An infrared thermometer can be used.
You can let it sit overnight and test it, and it should be very close to the currant air temperature.
You can run it to operating temp and it should match the thermostat temperature.

100 ohms would be to hot of a reading.

Yes, reading some ohm meters can be very confusing. I test some of mine by measuring a resistor I know the resistance of.

If I unplug the oxygen sensor and it runs better, what does that mean ?
A Bad sensor ?

This tells me if the computer is messing up the mixture.
A bad O2 sensor, exhaust leaks, or a cylinder or more that misfire, can mess up the fuel mixture command from the ECM.

P.S.
One last thing, the replacement EGR was positive pressure and they allowed it will work with right orifice washer, part was right according to cross reference to original negative pressure valve, and no OEM part available here. I used #42 washer and staked it in as per instructions, I guess it will work, they said money back if it don't....no more codes while running at any rate ???.....just still running crappy.

Nothing about this sounds good.
I would not use the cheap crap that you have to pick a washer and stake it in.
I know it is getting hard to find good parts.
A negative backpressure valve should be replaced with a negative backpressure valve, unless you are doing other modifications to change the system operation.
Most of the people that sell parts don't know spit.
The part software is full of errors.

There are many bad new parts being sold these days.
There are many wrong parts being sold.
The software that a store like NAPA uses must be piss poor by the questions the employees ask when looking up a part.
It looks to me like even the quality if the OEM parts sold by the dealers is declining at an alarming rate.

You could disconnect and plug the EGR hose, it and take it for a drive, and see if it runs better.

[Ripsaw]

Took replacement egr valve back for refund and got the old one cleaned and seating and passing vacuum test.

Re-installed and no change.

Disconnected O2 sensor and no change.

Disconnected and plugged egr valve and no change.

Hard to start this morning and acting like flooding out. Finally cranked for testing after holding throttle all the way open, and had to really open throttle to get it going, acting like it will die then catches up on half throttle and runs momentarily, only to surge up and down again and eventually, if not nursed, will die again. Real brain tickler here. I'm at a total loss of what to do next.

Could the pick-up coil in the distributor have anything to do with this, and could you walk me back through how to test the pick-up coil again, I lost my notes from last time when computer crashed, thanks.

Reason I ask, is my 89' would act similar until it quit starting altogether. Replaced distributor and runs like a champ again. Sometimes this 91' acts and sounds like a timing issue, but timing is right with that new chain.

[ChevyTech]

Pickup coil testing

500 to 1500 ohms between terminals.

Infinite from one terminal to ground.

When testing the pick-up coil resistance, the key should be off, and the pickup coil should be unplugged from the distributor module.

Inspect the magnet on the pickup coil to see if it is cranking into pieces. It should be one part.


If it floods out you should test the coolant sensor that the ECM monitors.
Also make sure the IAC works.

Here is a threads that talks about both:
http://67-72chevytrucks.com/vboard/s...d.php?t=322811

[Ripsaw]

Thanks tech. I gotta tell ya, this thing is making me nuts.

Couple quick questions.
If I take each plug wire and plug off an ohm through them, will it tell me if they are good, except for one that may be cracked and jumping fire I understand ?

Can't hear or see any fire jumping. Ran my hands over all wires while it was running and barefooted on wet grass, certainly would have found one if it was jumping.....heh heh.....

Pickup coil is good and magnet looks fine, and the coolant sensor and IAC valve.
Egr working, stumbles when diaphragm is pressed.

Engine still surging up and down and tach jumping with it. Even removed the fuel pump to check the new hose again in the tank but pressure was fine anyway.

Compression is about 93% on all cylinders and plugs look good, chalky tan with no oil.

No codes.

Runs fine at bottom of surge when idling and top of surge. But when it transitions from top of a surge to the bottom, it's like the computer can't catch up fast enough with the problem, and dies if I don't coax it a little with accelerator to keep it running.

The surge is fast, about half second or much less between each surge, top to bottom of rpm.

All out of ideas here, any are welcome from anyone.

[ChevyTech]

A bad wire could have given you a good shock you when you ran your hands up and down the plug wires.

The most common place for plug wires to leak is right at the spark plugs, and the spark jumps to the exhaust manifold heat shields, which is hard to see.

I like to watch them run at night when it is dark. Don't be surprised if you can see the plugs light up a bit when they fire. I also water test with a spray bottle and it is normal to see some light sparks dancing on the outside of the wires is you water test at night.

You can test the plug wires with an ohm meter to make sure you do not have an open wire. The longer wires will run a little more resistance then the shorter wires. Don't over look the coil wire. The coil wires do get open on these trucks.

If you have not checked to see if the distributor shaft will wiggle sideways, check it. When they are lose it messes with the RPM signal to the ECM.

Erratic idles is often caused by low fuel pressure on these trucks. Also check for vacuum leaks. Don't overlook the base gasket under the TBI unit which is a common failure part. Make sure the MAP sensor is getting good vacuum to it.

[Ripsaw]

FOUND IT !!!

Thanks to you again Tech.

You nailed it with the coil wire open. When I pulled the boot off the distributor side it looked like all the carbon silicone guts had been blown out of the wire through the end of it and was all over the top of the distributor center area. never seen that before, almost like a huge surge of electricity fried it. Cap is ok though, as is the terminal tip.

Tried to ohm it out and nothing, don't even know how it was running at all. Had an old wire I kept thankfully, and installed it. She is purring like a kitten again.

So now we know that not only will a timing chain cause surging idle, but so will a bad coil wire, egr valve, IAC valve, and coolant temp sensor, along with many others I assume.

So weird the way it was doing the exact same thing as it did before I fixed all that stuff last year. I guess they don't make coil wires like they use to, but then again, I am so old that when I first started working on them, they were actually made of real wire.

Can't thank you enough for your help, and last shot and ideas at trouble shooting, that found it for me Chevy Tech !

The good thing to come from all this, is it helped me learn how to troubleshoot better myself and review all the testing procedures that everyone needs to become more proficient at. I saved all the data on a thumb drive this time.

Now I owe you two beers and a deep sea fishing trip bud !

[ChevyTech]

Great!

You're welcome.

Glad you got it fixed.

Coil wires with the core burnt away like yours, is common on these trucks.

Yes, I remember my brothers using the old metal core plug wires. You could see it in the picture on the TV set when they drove in the driveway.