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egr solenoid


NAXJA Forum User
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


The ground is Pin A10 on the ecu.

Does the EGR solenoid click when you ground it directly?
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
I just read your post in the other forum. I usually come here first so my apologies for any duplication.
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?
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!
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.
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.
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.
Admittedly, I'm not sure under what conditions the ECU commands the solenoid to energize. As noted above, when energized, no vacuum is drawn from the egr valve which keeps it closed.

So just for fun, I warmed up my '88 and blipped the throttle while watching the egr. I could see the egr pintle move in response to throttle input. Then raised and held (around 2500) and saw the pintle fully open, then close as the exh backpressure equalized. Can't say if it completely closed. Repeated this a few times. Then unplugged the solenoid and did the blips again. I could not see any real difference.

Your high CO is due to a rich condition. Check your sensors, make sure your TPS is adjusted correctly and your air filter is clean. Go back to Cruiser's site for the details.
Most common cause for rich is a bad O2 sensor.

Once you correct the CO levels, your NOx will rise a bit. The rich condition cools the exh a bit and can lower your NOx levels. Once you clear this, exh temps may rise and increase NOx but the working EGR will keep them in check.
Yeah, I've been chasing a rich condition for a while. Got a smoke tester last week and found 4 vacuum leaks. Fixed 2 of the leaks (MAP TB port and MAT sensor). Unfortunately, 2 of the leaks are from the emissions equipment, temp sensor in the airbox and egr pintle. I'll bypass that temp sensor all together once it passes smog. I just have it connected to pass the visual inspection. Propped open the airbox blend door and it comes up to temp within 10 minutes. Holds tight at 195 pretty much. Sensors all seem to test fine.
The "sensor" in the airbox controls the servo at the front of the airbox. When cold, it allows vacuum to close the servo and pulls air in from the hose connected to the exhaust manifold. Once warm, it blocks vacuum and the servo opens to alliow fresh air in from the front of the airbox.

Mine went bad. Rather than replace it I popped the vacuum line off (from the vacuum harness and wrapped a small piece of electric tape around it and put the hose back on. Vacuum leak solved. It also looks "untampered". Just FYI, I took the hose to the exh manifold off one year and failed due to a "tampered" system.

If you want to replace it, here's the part on eBay.

I have 6 solenoids, 4 transducers, and 2 EGR valves.

If we could shut off that round opening/port of the EGR at the manifold, everything else would look just fine.