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

 

Pin A10 on the ECU.

Have you visited my website and completed Tips 1,3,4, and 5 yet?

 

Yes, added some comments there, learned a lot. I have cleaned many connections, now want to read harness resistances to see what is causing current issues

what i dont get is that my snap on scanner cycles once per second lean/ rich, while my Os sensor reading is pretty much steady.

 

Yes, the ECU provides the ground for the solenoid. Trying to measure resistance though, can be misleading since it's going through a transistor with a forward voltage drop. The small voltage across the solenoid tells me either you have a high resistance going through a connector or wiring, or the ECU isn't actually trying to switch the solenoid on. See what the voltage looks like on pin A10 at the ECU. The EGR solenoid for the canister only gets triggered in specific situations.

I'd guess your O2 reading has some averaging, versus the snap-on just showing instantaneous values.

 

I agree with above. However, remember the ECU doesn't create the ground, it closes the circuit between one side of the connector TO ground (via silicone circuitry). Check the grounds again.

 

I am really hating this jeep, the factory wire diagram is a flipping mess. the only egr solenoid shown lists it on the right hand fender well, and it calls it an egr evap canister solenoid. has the correct color wires for the egr solenoid that controls the vacuum signal to the egr valve, but that solenoid is on the left side fender next to aircleaner see image..

No where do I see the egr activating solenoid in the wire diagrams, just the "egr evap canister solenoid" ugh! I have NO solenoid valve associated with the charcoal canister.
Becuase of the schematic labeling I dont even know if I am tracing the correct wires to my egr solenoid, the one near the air cleaner. further that ten connector shown on the schematic above, well I am nkt sure which ten pin connector, as there is more than one hidden in the harness with ten pins, and there is no i.d. of the connector.



Now on my egr solenoid on the left fender near air cleaner I get the following on the plug when it is disconnected from the solenoid ...

Org/blk wire to chassis ground 3.7 volts with ignition ON, engine NOT running
Org/blk wire to grn /wht wire I get 3.7 volts when engine running*
org/blk wire to chassis ground 14 volts when engine running*
grn /wht wire to chassis ground 3.7 volts when engine running*
* cold engine at idle
Thus the solenoid does not activate when engine is running at cold idle cause it only has 3.7 volts across it. The egr per the manual is supposed to be disabled at idle by the solenoid being activated


Next cause my O2 sensor has an issue per my scan tool, and the rich smell of exhaust, I decided to,ohm out its center connector pin to ground, it should be a direct connection to chassis ground, and sure enlugh I get about 0.1 ohm or less. So that ground tests good.


So what is so screwed up here, why is that 3.7 bolts across my egr solenoid when it should be 12 volts?? what can cause that?

 

 

On my diagnostic connector shown above I get zero ohms <0.1 ohm on pin 7 (gnd) to battery negative, and I get 1.0 ohm on pin 8 (sensor gnd) to battery negative. Is one ohm acceptable for the sensor ground to battery? If acceptable, does this mean all my sensor grounds are good enough?

thanks!

 

Now that I've read this entire post. I've had this exact issue before. You're not going to like what it was for me... it was the ECU itself. After I replaced the computer with the one I have now, it doesn't do that. But, I have since removed the EGR and the solenoid. Before you go crazy, beg, borrow or steal another ECU. I'm willing to gamble that you'll solve your problem.

Nonetheless, yes, that is your EGR solenoid on the left fender, adjacent to the air cleaner box, on an angle bracket. And, yes, it is energized by the ECU providing ground while in open-loop mode when warming up, or WOT.

 

What if the solenoid was the issue?
How about removing the ECU and inspecting/cleaning the contacts in the receptacle?

 

the egr solenoid connector was unplugged for my measurements, The solenoid coil is reading 40 ohms across it, is 40 ohms correct? 12volt/40 ohm is 0.33 amp draw. Is that too much?

Also consider my O2 sensor did not work right per my scan tool, it would sometime stay at 2.1 volts for minutes, then suddenly go higher, then drop again, not normal behavior, my exhaust would be oderless, then start stinking rich randomly.
My sensor grounds appear good per the test I wrote about. I did the ground refresh a year ago at the dipstick mount, and that still tests good, my O2 sensor ground was really nice, low resistance back to battery neg. post. I passed smog just fine last year, it was remarkably clean. Something sure went bad

oh and another weird thing, yesterday on start up, I had the defogger on, cause I put the heater on full blast as I did a coolant change, and found the AC clutch, and electric radiator fan rapidly cycled on and off at idle, never had that happen before. I dont see any broken harness parts in the engine bay, no cut sheathing or other damage that I can see.

Thus the ecu may be wonky, but of course it could be the wiring to and from the ecu. I probably should pull it out and probe its connector, but I am not sure what I should be testing for on it. Any suggestion on testing the ecu and its connections? I will do that, but assuming the plugs and connectors look great, then what?

I can spend some more time tomorrow on testing, but I am rapidly running out of ideas other than the ecu. Sure I can try to redo the harness splices per your Renix tips, but my ohm reading on the O2 sensor shows no problems resistance wise, so I think those splices are probably good still, does that make sense?

Thanks!

 

Why not just refresh the connector on the ECU and check for continuity from A10?

 

I will be doing that after lunch, neighbor had a car issue, had to help, prius, ugh! battery leaked. had to clean it up rinse, baking soda etc... He wondered if the plastic was rusting! did not know the car body was made of steel, seriously, computer engineer! He is all thumbs when it comes to cars, he is a techie computer programmer, and can fix my interweb with his eyes closed, but when it comes to cars, oh well.

So the ecu wiring runs thru some connectors, ten pin connectors per the wire diagram, I got several ten pin connectors near the relay panel near the battery, so I need to figure which is which and also check those.

what bothers me is that supposed ground to the egr solenoid, triggered in the ecu has 3.7 volts on it relitive to battery negative. sure I can see a poor ground being a problem, but in this case it has power on it at 3.7 volts (measured at egr solenoid connector, connector removed from the solenoid) that is very unexpected, I cant figure how that happens???

 

Note from DJ
Here is some information on the operation of the EGR Valve EMISSION CONTROL

The ECU electrically controls the Exhaust Gas Recirculation (EGR) valve.

The EGR Is an ECU controlled solenoid valve that is used to control the EGR valves function. This valve is located on the left inner fender panel and its operation is controlled by the ECU in response to coolant temperature; throttle position, and manifold pressure.

Under conditions of engine warm-up [water temperature is below 115 degrees F or 46 degrees C] the engine is at idle, wide-open throttle, or rapid acceleration or deceleration, the solenoid valve is energized and blocking vacuum to the EGR valve. At normal operating temperatures with engine speed above idle, the solenoid valve is de-energized, allowing vacuum to the EGR valve. Now that the EGR valve is de energized it will allow some exhaust gases to be interred into the intake manifold.
If the Jeep is not meeting these requirements the ECU will not create a ground for the EGR valve to operate.

NOTE: If the electrical connector is removed from the EGR solenoid, the EGR flow of exhaust gases will be allowed at all times.

 

DJ. Thanks.

How does the Jeep run with the vacuum disconnected and plugged right at the EGR?