egr solenoid

[Black1990jeep]

On my 1990 renix 4.0 I am trouble shooting the ecu stuff.

On the egr solenoid valve which is located next to the fuel pump ballast resistor I get the following...

with ignition on I get 3.75 volt across the connector (between the orange/black wire and green/ white wire) this measured with connector removed from the solenoid valve.

I however get 14 volts measured Orange / black wire to chassis ground point.

My understanding is the solenoid should always have positive battery voltage on the Orange / black wire when ignition is on, and that the green / black wire is a switched ground via the e.c.u. I ohmed the green / black wire to chassis ground and get 45 ohms, thus not a very good ground.

where should I look for the poor ground? The manual is not clear as to the wire routing now what connector or splices there maybe in the path to ground.
I am losing near 10 volts someplace. the 3.75 volts is not enough to trigger the egr solenoid

thanks!

Suggestions?

[Saudade]

The ground is Pin A10 on the ecu.

Does the EGR solenoid click when you ground it directly?

[Black1990jeep]

Originally Posted by Saudade

The ground is Pin A10 on the ecu.

Does the EGR solenoid click when you ground it directly?

I have not tested the egr solenoid yet, but for sure its electric signal input is not correct. The solenoid allows egr operation when no power is to it, and is inoperative when the ecu supplies that signal, i.e. makes ground for the solenoid.

Additionally per my snap on scanner tool, my O2 sensor is not working right, its value is wrong, which of course might be also related to bad electricals. The O2 sensor is a fairly new.

I think I have systemic wire issues needing to be addressed. but I am not sure

[Saudade]

I just read your post in the other forum. I usually come here first so my apologies for any duplication.

[GravyDavey]

Reviving this old thread. It's smog time for me hear in San Diego. 1988 AT 4.0

I'm finding that the EGR solenoid allows vacuum to pass to the EGR valve when it has power from the ECU. My problem is that the ECU isn't opening the ground circuit at idle so I have the EGR valve is open all the time and of course that's stalling out the motor. I only hook up the EGR at smog time.

From other searches, it seems like I need to swap ECUs. Lucky me, I have a 90 ECU in there now, but I held on to my 88 ECU just in case. Before I get under my dash and try to get to that stupid 10mm nut, does anyone disagree with my synopsis?

[GravyDavey]

I just realized that I should double check the EGR solenoid by removing power to it. It should close off vacuum without power.

[GravyDavey]

Well, pulled the adapter off the EGR solenoid and it still lets vacuum through. So I guess I have a bad solenoid.

[cruiser54]

Just a reminder.
You folks that have to pass smog, make sure you complete Tips 1 through 5 at www.cruiser54.com first.
There's plenty of other tips regarding CPS, TPS adjustment etc.

[GravyDavey]

Thanks, Cruiser. I just tapped the Map sensor vacuum port on the TB after discovering a vacuum leak there.

I'm really trying to dial this thing since it now has a freshly rebuilt motor in it. The EGR valve leaks vacuum through the pintle. After I pass smog, I'm going to take the EGR off completely and cap the hole until I have to smog again.

Also discovered that vacuum diaphram for the airbox heater hose doesn't function. Out of curiosity I propped the blend door in the airbox half way open. I'm now coming up to temp in about 10 minutes which is a major improvement. Hoping for more mpgs!

[cruiser54]

We need to come up with a solution for the pintle issue.
I would love to be able to seal that internally while it appears stock from a visual standpoint.

[Saudade]

Actually, the EGR will get vacuum if you disconnect the harness. When the solenoid is "de-energized", the vacuum source (intake manifold) is connected to the vacuum controlled device (the EGR, more specifically, the transducer). The transducer then operates off exh back pressure to pass or vent vacuum to the valve.

With the solenoid energized by the ECU, the controlled device (the egr) is cut off from the source, and the vac line to the egr is vented. So just disconnect the plug and apply 12v across the solenoid terminals and listen for the clicking. If it clicks, so far so good. Then use a vacuum pump, or a clean hose and your mouth and draw/blow on the source port with the solenoid off, you should be able to draw/blow air (no vacuum). Then energize the solenoid. You should not be able to draw/blow air (now can pull a vacuum). If you blow through either of the other 2 ports, air should pass.

While internally blocking the EGR sounds plausible, here in CA smog test includes the tailpipe sniffer. A blocked EGR could cause enough rise in NOX to fail.

[cruiser54]

There are reports of folks passing kommiefornia smog with a non functioning EGR valve.

[Saudade]

I'm sure there are. As long as it "looks" OK, and passes the sniffer. Some places perform a very lax visual inspection. Some are very scrutinizing.

[GravyDavey]

Thanks, Saudade. That's a good explanation of how it works. I described it the opposite way when I jumped to the conclusion that something was wrong with the ECU. It was allowing vacuum to the EGR at all times.

I tested for continuity across the solenoid terminals. Tested open, so dead by that test too. Luckily my buddy a block away has an 87 so I borrowed his solenoid for my smog test. Just barely failed, slightly high CO on the 25 mph test. NOx was super low so the EGR does work.

I put on a new cat yesterday, so should pass with no problem today.

However, I have a question. Does anyone know of a source for a new/used EGR solenoid? This is the 2nd one that has died on me. It looks like the YJ used the same part. I wonder if another 2 wire solenoid which allows vacuum while powered might work, but that is going to take some serious googling to figure out.

[cruiser54]

I might have some.