Okay, In my quest to try to get rid of my pinging problem, I have now moved on to the EGR system. BTW the car is an 85'. Anyway, The EGR valve is good. It holds vacume, and it opens and closes easily. So I moved onto the soleniod. I followed the instructions in my service manual. I removed the vacume harness from the solenoid, left the diognostic port grounded, and hooked up a vacume pump to the manifold/engine side. The solenoid wouldn't hold vacume, it just came out the other port. So with the key in the on position, I ran a test light accross both terminals of the solenoid plug. No light. So I hooked the test light to a ground, and tried each terminal. One lit up, and one didn't. According to my manual (Haynes), I am supposed to check for an open curcuit. This is a cut wire I'm assuming??? Anyway, if no open curcuit is found, then it says to hook up an OHM meter to the solenoid and make sure it get's atleast 20ohms. I have an ohm meter, but I don't really know how to use it. under the "ohm" section, there are different settings (20M, 200K, 20K, 2K, 200). Anyway, if I don't get 20ohm's then I'm supposed to replace the solenoid and the ECM, according to the manual. Is this right? Is there a better way to test the solenoid??? What should I do??? If you haven't been keeping up on my "85 Vette still pinging" thread, here is the link http://forums.corvetteforum.com/showthread.php?t=997991

I am starting to get really frusterated with this car. Your help would be GREATLY appreciated.

 

The Pnk/Blk wire from the Gauges fuse supplies power to the EGR Solenoid; the Gry wire is the control wire to the ECM. When the ECM grounds the Gry wire the Solenoid opens and applies vacuum to the EGR Valve.

At normal idle or with the key On there should be +12Vdc on either wire as the ECM is NOT calling for EGR. This means that the test light should be On when touched to either location.

Set your ohmeter on the lowest fixed scale or set it to Auto mode when trying to measure low resistance, like 20 Ohms.

Since you have a DMM you can measure voltage on either wire of the Solenoid, better than using the test light.

Also, I have a simple EGR test method on site.

 

Is there a chance your ecm is putting the motor into an intermittent super lean and/or super rich condition? The intermittent smoke symptom is a clue (rich). So if it does that, it may do the opposite too (lean when it shouldn't be). I might guess ecm or chip malfunction. It would be a LOT easier if the thing threw codes for the MAF or TPS. Or at least a lean code. The fact that it doesn't throw codes indicates either it is a problem that the ecm does not normally recognize anyway, or a problem with the ecm/chip.
Usually the EGR will cause a more faint ping at highway speeds. But you get it at times and conditions that are inconsistent with that.
Last, it might be something like an intake manifold vacuum leak. If it's breached in the right spot, it might suck some oil in along with air to account for the smoke. I had that happen on my car. You can test for intake leaks with propane (no, not lit) or choke cleaner. But if it's an internal leak or way in the back, you might not find it. I couldn't find mine, but it was there. I finally just took things apart enough to gain access to all the torx bolts holding it on, and cranked them down. Some were real loose. Then, no more intermittent smoke, and it quit all the funny business. That's worth a try. It's only going to be a couple hours and costs nothing. You do have to take the runners off to get at some of the bolts.

 

What worries me is that I only get 12 volts to the pink and black wire when I turn the key on. If it is true that I should be getting power to both wires, then what could be causing the lack of power to the other???


Here is my thinking.

a. when I pulled the plenum off, there was a lot!!! of carbon build-up and black crud.

b. I am not getting 12 volts to the grey wire on the EGR solenoid plug when the key is on. I get 12 volts to the pink and black wire though.

c. so if the solenoid isn't getting a 12 volt signal from the ECM, then the solenoid is always open, allowing the EGR valve to stay open as long as the engine is creating vacume.

d. SO... the EGR valve is always allowing exhaust back into the intake (like at WOT on the freeway) and that would cause a ping/knock, and under heavy load, and would also be the cause for the carbon build-up in the intake system


does that logic make sense???? and if so, why am I not getting a code from the ECM...BUT MORE IMPORTANTLY, WHAT IS THE CAUSE???

 

You have one of several conditions:
-the EGR Solenoid windings are open
-the Gry wire is shorted to ground
-the ECM is faulty

Pull the electrical plug from the EGR Solenoid, jumper the Pnk/Blk wire to it's pin on the Solenoid, turn the ignition On and measure voltage on the other solenoid pin. If you still see +12Vdc on one pin and not on the other, replace the Solenoid.

If +12Vdc is found on both pins, wring out the Gry wire back to the ECM in search of a ground.

If no short to ground is found in this wire, suspect the ECM driver.

 

Set your meter to the 200 setting, unplug the electrical connection to the solenoid and measure the resistance of the soleniod windings. A reading of "zero" indicates the solenoid windings are "open" and will not allow current to pass through the windings....and the solenoid will not work. If you have an ohms reading (guess to be 10 to 20??), the windings are good and applying voltage to one solenoid terminal will cause the other terminal to have the same voltage (when measured to ground). Hope this makes sense! Do not assume the solenoid is good if it has resistance as the plunger (or valve) may be stuck either open or closed.
SAM

 

So... I checked the solenoid with the ohm meter. It says it's good. Assuming that it's not stuck in the open or closed position. I got 25ohms when I checked it. So I'm going to try putting 12 volts to the pink/black wire prong, and just grounding the grey wire prong. Doing this should close the solenoid and cause it to hold vacume right??? And if it does, then either the ECM is bad, or the grey wire is cut somewere between the solenoid harness, and the ECM harness. Is this thinking right??? Thanks again for your help. I feel like I'm almost there.

 

okay, I plugged the solenoid into it's harness, turned the key on, and ran the test light from a ground, to the grey wire. What do you know, it worked. The solenoid clicked on, and the test light lit up. Then I tried the vacum test and the solenoid was able to hold vacum. So. Now that I known that the solenoid is good, that means that I either have a bad ECM, or the grey wire is cut somewere. Can I run the ohm meter from the grey wire on the solenoid harness, to the same wire on the ECM harness to make sure that the wire isn't cut? And if so, what terminal is the grey EGR wire at on the ECM harness???

 

On my '88 it's pin A4 of the ECM. First disconnect the battery leads.

Once you drop the right hush panel and the ECM, lower the ECM and touch some metal on the car. After you ground any static charge in this manner do not move around on the carpet until the connectors have been plugged back into the ECM.

 

okay, I pulled the ECM down, and checked the A4 wire with the grey wire on the solenoid harness with the ohm meter and I got a signal. So the wire is good. That only leaves the ECM. So I guess I will be looking for a used computer now. UGH!!! Thanks everyone for all your help. Is this a common thing with these computers??? In all my years and all the cars I've owned, I've never had to replace a computer. Of course I've always owned imports. No offense to domestic cars of course at all

 

OK, so my question is did you see a vacuum level change when you applied power to the EGR Solenoid terminals??

 

well before, when the solenoid wasn't getting power, it wouldn't hold vacume. It was open, and would just leak the vacume out the other port. When I put power to the solenoid manually, I was able to make it hold vacume with no problem. When I took the power off of the solenoid, the vacume dropped back down. That was how I was able to confirm that the solenoid was still good. Is there any other test I should perform b4 I assume that the ECM is bad???

 

Kcpaz: this is a long shot, but a little "dirty" work may save you from having to buy an ECM for the Vette. Most computer controlled wires all pass through a main connector located just behind the battery on firewall of your car. This "big" connector has some "gunky stuff" inside it and this stuff can actually cause connection issues between the ECM and sensors, solenoids, etc. This joint can show continuity but will not allow ample current to pass and activate devices such as a solenoid. I wish I had taken a picure of the connector on my 89. This is about a two - three hour job and you car will be better off after you do it. If you are interested and need more info, send me an email to samlam@charter.net. Good luck with the problem!
BTW, I was having problems with my cluster diming and was about to send her off for repairs. Another forum member suggested this cleaning .....and it worked. The issue that caused my problem may be causing yours!
SAM

 

Thanks for the tip. if the ECM doesn't fix the problem, then I will give it a try. However, when I hooked the ohm meter to the grey wire, I didn't just get low voltage numbers...it was just flat out dead. I got nothing. But it may be a good idea to clean it anyway. Thanks

 

Make sure that Gry wire is neither open nor shorted to ground before buying another ECM.

Did you remove the connector from the ECM and measure resistance of the Gry wire between the ECM connector pin and the Solenoid pin?

Measuring from one end of that wire to the other you should get 0 Ohms on the 200 Ohm scale if the wire is ok.

Also, with the wire not connected to the ECM measure resistance between the Solenoid pin end of the wire and ground. Here you should see very high resistance.

 

when measuring from one end of the grey wire to the other at the 200ohm setting, I get 0.2ohms. When I go from the grey wire prong, to ground, I don't get a reading on the ohm meter. It doen't react at all.

 

kcpaz, I sure hope you get this figured out...I've been too busy (sometimes lazy) to get my very similar situation solved. Thanks for your persistence in getting some answers!

 

Okay, It's been a long time since I updated this thread so now that I got another computer, I figure it's time to start the madness again. So here we go. I replaced the ECU with another one, and still the pinging problem was there. So I looked into it a little more. I tried turning the key to the on position, and putting a test light between the two wires on the EGR solenoid harness. With the key on, I still got no action on the test light. So just for fun, I started the car and tested it again. This time, the test light went on. Hurray, I finally got some action at the harness. The problem seems that the ECM is activating the EGR solenoid at the wrong time. Could someone please fill me in on how exactly the ECM is supposed to control the EGR solenoid!!! The manual I have SUCKS and the testing instructions are confusing. I know that 65Z01 has helped me in the past and seems to know alot about the L98 Electrical System. Maybe someone else will be able to shed some light on my problem.

 

You can insert a vacuum T into the line between the EGR solenoid and the EGR valve, lay the gauge under a wiper on the windshield and see if the EGR is comming on while cruzin.

Also, try running a 160deg T-stat which will lower engine and combustion temps.

 

Just for fun I tried putting the PROM from the other computer in. The other computer was from an 85' Trans Am. When I drove it, the fuel mileage information in the dash was doing some funny things but the ping was almost completely gone. Could it be that my old PROM had been tampered with or had gone bad? Could that cause a ping?