Author Topic: EGR and Solenoid Troubleshooting  (Read 730 times)

Offline Ol Blue

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EGR and Solenoid Troubleshooting
« on: March 11, 2018, 02:15:58 PM »
I have a 1987 V10, 350 TBI stock truck. The motor was replaced at the dealership in 1999 and has about 60,000 miles on it. I am the second owner and have been slowly taking care of small issues since I got it December 2017.

I have read up a bunch on how the EGR works and what it does -- on this forum and in a 1987 drivability and emissions service manual I recently acquired, but I am still having an issue. I replaced the EGR solenoid with a Delco one because the old one was brittle and I broke one of the ports off when replacing vacuum lines. I do not know if the old one worked properly or not, although I can say I wasnt getting a check engine light previously.

Basically with the EGR hooked up properly, the truck runs poorly. With the vacuum hose disconnected between the solenoid and the EGR (plug the vacuum line with a screw) the truck runs perfectly--- but I get a code 32 (EGR system failure)

With a cold engine and engine running I can hold the brake, in DRIVE, and when I 'blip' the throttle the solenoid opens and pulls about 15-20 in Hg of vacuum. When all vacuum lines are hooked up properly, this causes terrible idle, because it is opening the EGR, and not under the conditions normally required (cruising down a flat road, engine warm). When I do the same thing with a vacuum gauge between the solenoid and the EGR it runs great but the solenoid is allowing vacuum through it, attempting to open the EGR valve.

I removed and rebuilt (resealed) the throttle body yesterday and while the TB was off, I removed and inspected the EGR and it "seems fine". One thing I have done to test the EGR itself is with the engine running I have sucked on the hose to the EGR with my mouth ( I dont have a vac pump) and it of course caused a terrible idle while I was doing that. I can make the EGR actuate by sucking on it (sounds weird) and the pintle and passages are black but not blocked.

 The service manual says The ECM uses engine coolant temperature, the TPS- off idle and the MAP sensor to control the EGR solenoid. Should I replace the MAP sensor and the TPS? (edit-- the engine coolant temp sensor sending unit is new)

Thank you for reading this and let me know what you think.

« Last Edit: March 11, 2018, 02:24:11 PM by Ol Blue »

Offline Irish_Alley

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Re: EGR and Solenoid Troubleshooting
« Reply #1 on: March 11, 2018, 08:34:50 PM »
Like you already under stand the egr shouldn't open till certain conditions are meet. Just one faulty sensor CATS shouldn't allow the egr to open. I'm thinking maybe it's a bad egr solenoid and it's allowing vacuum to pass it under certain conditions when it shouldn't at all. I wouldn't take my post as a automatic response to get a new solenoid,but wait till bd responds or someone else
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Online VileZambonie

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Re: EGR and Solenoid Troubleshooting
« Reply #2 on: March 12, 2018, 07:24:49 AM »
Was the truck originally equipped with a 350 or 305? They use different parts but often people think a 350 is a direct swap. The EGR sol is specific to your truck, what's the GVW? Do you have a picture of the VECI label? Make sure you have the vacuum lines to the solenoid hooked up correctly. Make sure that none of the wiring is compromised or grounding. If everything looks okay you probably have the wrong part or defective one, just follow the diagnostic tree. Buy a vacuum pump instead of sucking on your hose. Here is some additional info:

CIRCUIT DESCRIPTION
The Electronic Control Module (ECM) operates a solenoid to control the Exhaust Gas Recirculation (EGR) valve. This solenoid is normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass to the EGR valve.
The ECM control of the EGR is based on the following inputs:

Engine coolant temperature - above 25°C.
Throttle Position Sensor (TPS) - "OFF" idle
Manifold Absolute Pressure (MAP)
If Code 24 is stored, use that chart first.
Code 32 will detect a faulty solenoid, vacuum supply, EGR Valve or plugged passage. This chart checks for plugged EGR passages, a sticking EGR valve, or a stuck open or inoperative solenoid.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

Checks for solenoid stuck open.
Checks for solenoid always being energized.
Grounding test terminal should energize solenoid and vacuum should drop.
Negative back pressure valve should hold vacuum with engine "OFF".
When engine is started, exhaust back pressure should cause vacuum to bleed off and valve to fully close.
DIAGNOSTIC AIDS
Before replacing ECM, use an ohmmeter and check the resistance of each ECM controlled relay and solenoid coil.
See ECM wiring diagram for coil term. I.D. of solenoid(s) and relay(s) to be checked. Replace any solenoid where resistance measures less than 20 ohms.
On engines with an ECM, the EGR System is called "Pulse Width Modulation" (PWM), which means the ECM turns the solenoid "ON" and "OFF" many times a second and varies the amount of "ON" time (Pulse Width) to vary the amount of exhaust gas recirculation.

EGR Bleed Solenoid

On 5.0L and 5.7L Federal engines with light duty emissions and automatic transmission, an EGR bleed solenoid is connected in the transmission converter clutch circuit. When the transmission converter clutch applies, the solenoid is energized and the vacuum to the EGR valve is reduced to about half normal value.
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Online VileZambonie

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Re: EGR and Solenoid Troubleshooting
« Reply #3 on: March 12, 2018, 07:27:52 AM »
and for DTC 32....


CODE 32 - EGR SYSTEM FAILURE (UNDER 8500 GVW)

Circuit Description :
The ECM operates a solenoid to control the Exhaust Gas Recirculation (EGR) valve. This solenoid is normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass to the EGR valve.

The ECM monitors EGR effectiveness by de-energizing the EGR control solenoid thereby shutting off vacuum to the EGR valve diaphragm, With the EGR valve closed, fuel integrator counts will be greater than they were during normal EGR operation. If the change is not within the calibrated window, a Code 32 will be set.

The ECM will check EGR operation when:

Vehicle speed is above 50 mph.
Engine vacuum is between 40 and 51 kPa.
No change in throttle position while test is being run.
Test Description : Step numbers refer to step numbers on diagnostic chart.
Checks for solenoid stuck open.
Checks for solenoid always being energized.
Grounding test terminal should energize solenoid and vacuum should drop.
Negative back pressure valve should hold vacuum with engine "OFF".
When engine is started, exhaust back pressure should cause vacuum to bleed off and valve to fully close.
Diagnostic Aids :
Before replacing ECM, use an ohmmeter and check the resistance of each ECM controlled relay and solenoid coil. See ECM wiring diagram for coil term. I.D. of solenoid(s) and relay(s) to be checked. Replace any solenoid where resistance measures less than 20 ohms.
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Offline Ol Blue

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Re: EGR and Solenoid Troubleshooting
« Reply #4 on: March 12, 2018, 05:04:09 PM »
First thank you for the responses. I am grateful- seriously.
Yes, the truck was 350 originally.
When I purchased the Delco solenoid from rock auto, I did not see an option to select GVW, only 1987, V10, 5.7 350
And for what its worth, the new solenoid matched the old one as far as looking at it.

I have just assumed the truck was under the 8500Lb delineation. Where can I get the correct GVW on my truck? I am now looking at the picture in the service manual of the under 8500 GVR EGR system (fig 9-8) and thats what mine looks like versus the over 8500 GVR picture (fig 9-9).

It sounds like the first thing I need to do is determine the GVW and then get me a little Mighty Vac MV8500 vacuum pump- I have seen this name thrown around, I just assume its the one to get. Then I can start down the diagnostics road properly. And inspect wiring for possible grounding.

When the service manual instructions say: "ground diagnostic test terminal" this is referring to inserting the jumper wire across A and B terminals under the steering column, correct? This should energize the solenoid and cause a drop in pressure? ( engine off, key on)

I can's seem to find a VECI label although the truck hasn't been monkeyed with too much and has all original paint, so I would expect that if it is supposed to be there it would be there. Is this a state-to-state thing? Where should this label be?

And lastly when it gets into testing OHMS of resistance of any relays and solenoids, that's when it really gets over my head---- although, to be fair to me, this EGR system was over my head 2 weeks ago and thanks to this forum, I'm slowly getting it!! If you have any tips on that testing resistance, I'll take em. But first I will start with the vacuum stuff.
I will include a pic of the label I have under the hood.

I am very interested in this truck and its operation. Thanks in advance for any answers to the above questions






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Re: EGR and Solenoid Troubleshooting
« Reply #5 on: March 12, 2018, 05:35:44 PM »
I'm sure you are under the GVW but over the years people swap things and butcher these trucks so I had to ask. You don't need to get crazy with the testing, if you just bought it see if they will send you another one. Have a test light and a vacuum gauge or vacuum pump handy and we can walk you through simplified testing.
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Offline Ol Blue

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Re: EGR and Solenoid Troubleshooting
« Reply #6 on: March 12, 2018, 07:15:25 PM »
Mr. Zambonie,
Thanks a bunch. I should have a vacuum pump here in two days.

Offline Ol Blue

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Re: EGR and Solenoid Troubleshooting
« Reply #7 on: March 14, 2018, 05:41:59 PM »
OK, I received my vacuum pump today and did some testing.

These numbers will correspond to the EGR System Check (under 8500 GVW)
1. Vacuum source to EGR solenoid is 21 in/Hg
2. No.  Vacuum does not drop
3. Yes. Ground test terminal (AB under steering column) vacuum drops to zero.
4. OK. I attach vacuum pump to the EGR side of the solenoid with engine off. I remove the foam from the "vent" and attach vacuum pump there. It takes about 5 in/Hg to open EGR valve and it will hold 10 in/Hg for over 20 seconds. It will not hold more vacuum than 10 in/Hg. Once vacuum is released, the EGR valve appears to move to seated position.
5. Not OK.  I applied 10 in/Hg to EGR solenoid (via the "vent") which held open the EGR valve. I started engine. The valve did not move to the seated position. The vacuum pump held its 10 in/Hg and she ran terribly.

According to the service manual since #5 is not ok, remove EGR and check passages. If they are not plugged, replace EGR valve.

So if i trust this process, my thought is that the solenoid is good and if I'm going to take the EGR valve off to inspect it, I am just going to replace it.

I am certainly interested in more information if ya got it.
Thanks in advance!!



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Re: EGR and Solenoid Troubleshooting
« Reply #8 on: March 14, 2018, 06:34:06 PM »
If the EGR valve itself is sticking then just replace it.
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Offline Ol Blue

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Re: EGR and Solenoid Troubleshooting
« Reply #9 on: March 14, 2018, 09:25:12 PM »
Do you mean sticking open or closed? It seems like it opens when it's not supposed to. And then shuts again.
Here is pics of engine running, vacuum gauge attached to EGR side of solenoid.

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Re: EGR and Solenoid Troubleshooting
« Reply #10 on: March 15, 2018, 02:09:38 PM »
Are you sure your hoses aren't reversed on the solenoid? Sounds like they are. That should be the supply to the solenoid and the other line should go to the EGR valve.
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Offline Ol Blue

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Re: EGR and Solenoid Troubleshooting
« Reply #11 on: March 15, 2018, 04:04:51 PM »
Here is how I have it routed, and labeled as I understand it. It is normally mounted to  bracket, it's laying down just for the picture.

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Re: EGR and Solenoid Troubleshooting
« Reply #12 on: March 15, 2018, 04:39:06 PM »
So unplug the electrical connector and see if you get the same readings performing the same test on the gauge. If you do then the solenoid is bad.
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Offline Ol Blue

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Re: EGR and Solenoid Troubleshooting
« Reply #13 on: March 15, 2018, 05:06:42 PM »
Ok. That makes sense to me. I will do that.
Thank you

Edit: Alright, I attached the gauge the the EGR side of the solenoid today with the electrical connector hooked up. Same result as pic before. Idle no vacuum. Press the gas pedal and speed up RPM maybe 200, then it pulls vacuum when it shouldn't.
Next, I unplug the electrical connector and repeat the test and no vacuum is detected at either idle or at just above idle.

It seems that the solenoid is good. I am leaning toward replacing the EGR valve with an AC Delco one from rock auto for $43 bucks. The spring must be weak or perhaps there is some internal carbon that won't allow the negative backpressure valve to "do it's thing".

At step #4 on EGR system check, the vacuum would hold for 20 seconds but it would not hold more than 10in/HG.
« Last Edit: March 15, 2018, 05:44:00 PM by Ol Blue »

Offline Ol Blue

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Re: EGR and Solenoid Troubleshooting
« Reply #14 on: March 29, 2018, 06:27:59 PM »
I got a new AC Delco EGR valve from rock auto and finally installed it today. It seems to have fixed the problem because it is now hooked up to the solenoid and she runs great.