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I have recently bought a 1989 F-150 with a 5.0 l V8. I'm in California have failed smog twice now due to too high NOx emissions. The EGR valve does not open at all (smog guy verified this for me on the "dyno" as I don't think the valve should open at idle, so I can't test it myself).
I have tested the vacuum lines going to the valve, and replaced valve itself, and all of that is fine. If I apply a vacuum to the appropriate line with a running engine, the idle gets rougher, and I see the valve opening. If my understanding is correct, the problem must be in the solenoid, in the wiring leading up to the solenoid, in the ECU, or in some other sensor informing the ECU to open the EGR valve.
I have replaced the EGR solenoid, and Oxygen sensor. I unfortunately don't know how to test the solenoid ... I think I broke a previous one by shorting it out. I thought I could trigger the solenoid if I used a jumper wire to ground it (it's already getting +12V on one of the wires), but when I did that, nothing happened except for a spark! And after that, I read virtually no resistance across the solenoid. I've since replaced it again and NOT tried that same "test"; now I'm reading a resistance of about 40 Ohms across the brand new solenoid, which I assume means it's ok? (Side note, how would I properly test the solenoid?)
One thing to mention is that the original connector on the wiring harness side to the solenoid is no longer there. Instead, two blade connectors are crimped to each cable and it's connected to the solenoid that way. (It was a farm truck before and some of the repairs look a little rough.) So I think it's possible that the wires are connected the wrong way around.
Another thing to note is that I have no check engine light or any codes. So the computer does not seem to know or care that the EGR valve never opens.
That leaves me with the following questions:
Since I don't have the original connector, what is the correct way to wire up the solenoid? Which side gets the +12V, left or right?
Are there any sensors that I should check that "inform" the ECU of the state so it can make it's EGR decision?
More broadly, where would a person more experienced than me look next? I'm kind of at the end of my rope of how to troubleshoot this.
It would be awsome if anyone had any pointers for me. I just started this project (it's actually my first project car) and it would suck to have to give it up because I can't get it smogged before I can even really start.
Just realized I put this in the wrong forum, sorry. It's a 1989 of course. I can't seem to move it myself (or delete and recreate), so if a moderator could do that, that would be great.
(Moderator note: Thread moved)
Last edited by 85e150; Apr 16, 2022 at 12:20 AM.
Reason: moved thread note
1. first pic where does, red vacuum line, go from solenoid?
2. check your coffee can on passenger side wheel well, for leaks(know to rust out, or check valve go bad), EGR takes 4inhg to open, it will open at low, steady state, speed, and/or cruise speed, not at idle, or WOT.
Were the wires attached to the solenoid when you shorted it? If so you have likely blown the driver in the PCM, that would explain why there is no movement from the EGR. Have you tried to pull codes? You should get the all clear 11 code at the very least, if you don't even get that this also suggests there is a problem with the computer and you need to replace it.
Since I don't have the original connector, what is the correct way to wire up the solenoid? Which side gets the +12V, left or right?
Are there any sensors that I should check that "inform" the ECU of the state so it can make it's EGR decision?
More broadly, where would a person more experienced than me look next? I'm kind of at the end of my rope of how to troubleshoot this.
1 - +12v red wire driver's side, Green passenger side. Green is ground, and the computer uses pulse width modulation that grounds the pin, activates solenoid opens vacuum to EGR valve and it opens.
2- The EGR three(3) wire is a positioning sensor that tells the ECU its position. Basically during part throttle/cruise is the only state where EGR is active.
3- Using a volt meter, test the solenoid and sensor. If those check out, test continuity of wires, between pins and plugs. Use a volt meter or test light, check for codes directly at the test plug, don't rely on your CEL bulb.
Test that your EGR opens, simply suck on the vacuum hose, and plug the hose. Should stay open, if not, you got a vacuum leak, or a bad vavle.
1. first pic where does, red vacuum line, go from solenoid?
2. check your coffee can on passenger side wheel well, for leaks(know to rust out, or check valve go bad), EGR takes 4inhg to open, it will open at low, steady state, speed, and/or cruise speed, not at idle, or WOT.
1. It goes to the engine and when I unplug it while it's running I can feel a vacuum on it with my finger. Haven't measured the pressure (don't have the tool) though.
2. Will do. Will this affect my vacuum on the red line?
Originally Posted by Conanski
Were the wires attached to the solenoid when you shorted it? If so you have likely blown the driver in the PCM, that would explain why there is no movement from the EGR. Have you tried to pull codes? You should get the all clear 11 code at the very least, if you don't even get that this also suggests there is a problem with the computer and you need to replace it.
They might have been, I unfortunately do not remember clearly. I think I had the +12V connected and unplugged the ground from the solenoid.
How would I test the PCM driver? Or should I just replace the computer and hope for the best?
Haven't tried to pull codes yet, since I was not getting a check engine light. But I will do so as soon as I get to it.
Originally Posted by wwhite
1 - +12v red wire driver's side, Green passenger side. Green is ground, and the computer uses pulse width modulation that grounds the pin, activates solenoid opens vacuum to EGR valve and it opens.
2- The EGR three(3) wire is a positioning sensor that tells the ECU its position. Basically during part throttle/cruise is the only state where EGR is active.
3- Using a volt meter, test the solenoid and sensor. If those check out, test continuity of wires, between pins and plugs. Use a volt meter or test light, check for codes directly at the test plug, don't rely on your CEL bulb.
Test that your EGR opens, simply suck on the vacuum hose, and plug the hose. Should stay open, if not, you got a vacuum leak, or a bad vavle.
1. That's very interesting, in that case it was originally hooked up the wrong way around. Probably the root cause of what caused the solenoid to fail (and then I made it worse by shorting it too).
2. Got it. Easiest way to test that one would probably be to manually apply vacuum and see if the signal on one of the three wires changes?
3. Thanks, those are great next steps, really appreciate it. For testing the solenoid, I just measure resistance across it? For testing the sensor, I can just check it as described in (2)? I already did do the last test and found no vacuum leak and good valve.
Codes can be set without triggering the check engine light. There is no test for the output drivers in the PCM but at this age it wouldn't be surprising to find it has leaking caps or has water/corrosion damage. So try to pull codes and then remove it for a closer inspection, and based on what you find with that decide if a replacement is warranted.
