EGR issues
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EGR issues
So glad I got that code18 issue off my back, but now I can't seem to get away from the 34. I've tried two other EGRs and EVR sensors from other parts sitting around and one off my brothers 97 F250 that works fine, but I'll pull the battery cable to clear EEC memory and it'll still come back. I checked vacuum lines, everything checked out alright.
Could it be the CAT if it were plugging up creating more backpressure. I'd want a second opinion before I punch it out and try it. If that fixes it, I'll get another CAT.
I checked the EVR valtage with key off and got 5V, my book calls for about 5K Ohms and I gotten a little shy of 5K.
Could it be the CAT if it were plugging up creating more backpressure. I'd want a second opinion before I punch it out and try it. If that fixes it, I'll get another CAT.
I checked the EVR valtage with key off and got 5V, my book calls for about 5K Ohms and I gotten a little shy of 5K.
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Freshman User
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So glad I got that code18 issue off my back, but now I can't seem to get away from the 34. I've tried two other EGRs and EVR sensors from other parts sitting around and one off my brothers 97 F250 that works fine, but I'll pull the battery cable to clear EEC memory and it'll still come back. I checked vacuum lines, everything checked out alright.
Could it be the CAT if it were plugging up creating more backpressure. I'd want a second opinion before I punch it out and try it. If that fixes it, I'll get another CAT.
I checked the EVR valtage with key off and got 5V, my book calls for about 5K Ohms and I gotten a little shy of 5K.
Could it be the CAT if it were plugging up creating more backpressure. I'd want a second opinion before I punch it out and try it. If that fixes it, I'll get another CAT.
I checked the EVR valtage with key off and got 5V, my book calls for about 5K Ohms and I gotten a little shy of 5K.
Sorry I meant KOEO for the voltage and ohm test.
Lead Driver
Joined: Sep 2002
Posts: 9,182
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From: Gateway to the West
Code 34 indicates that the voltage RECEIVED FROM the EVP sensor was higher than it should be when the EGR valve is fully closed. If the voltage coming FROM the EVP is the SAME as the voltage going TO the EVP, the EVP is shot. (The voltage increases as vacuum decreases but NEVER gets as high as the voltage coming from the ECM to the sensor).
Is your voltage check the output voltage from the +5VDC (VREF) power supply in the ECM or from the EVP BACK to the ECM? You should get really close to +5VDC from the VREF pin on the EVP. The concern is whether or not the return voltage (SIG RTN) FROM the EVP back to the ECM is within spec. Even fully closed, the return voltage FROM the EVP should not be the same as the voltage coming TO the EVP from the ECM.
The other thing to determine would be whether or not the EVR is actually working. The EVR gets "told" to open and close by the ECM.
ECM - Engine Control Module (computer)
EVP - EGR Valve Position sensor (atop the EGR valve)
EVR - EGR Vacuum Regulator solenoid (inline with EGR vacuum supply)
Apologies for the incomplete info here but I am not at home and cannot reference wiring diagrams to tell you which wires (colors) to actually perform the checks on. I can look it up and post later.
Is your voltage check the output voltage from the +5VDC (VREF) power supply in the ECM or from the EVP BACK to the ECM? You should get really close to +5VDC from the VREF pin on the EVP. The concern is whether or not the return voltage (SIG RTN) FROM the EVP back to the ECM is within spec. Even fully closed, the return voltage FROM the EVP should not be the same as the voltage coming TO the EVP from the ECM.
The other thing to determine would be whether or not the EVR is actually working. The EVR gets "told" to open and close by the ECM.
ECM - Engine Control Module (computer)
EVP - EGR Valve Position sensor (atop the EGR valve)
EVR - EGR Vacuum Regulator solenoid (inline with EGR vacuum supply)
Apologies for the incomplete info here but I am not at home and cannot reference wiring diagrams to tell you which wires (colors) to actually perform the checks on. I can look it up and post later.
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Code 34 indicates that the voltage RECEIVED FROM the EVP sensor was higher than it should be when the EGR valve is fully closed. If the voltage coming FROM the EVP is the SAME as the voltage going TO the EVP, the EVP is shot. (The voltage increases as vacuum decreases but NEVER gets as high as the voltage coming from the ECM to the sensor).
Is your voltage check the output voltage from the +5VDC (VREF) power supply in the ECM or from the EVP BACK to the ECM? You should get really close to +5VDC from the VREF pin on the EVP. The concern is whether or not the return voltage (SIG RTN) FROM the EVP back to the ECM is within spec. Even fully closed, the return voltage FROM the EVP should not be the same as the voltage coming TO the EVP from the ECM.
The other thing to determine would be whether or not the EVR is actually working. The EVR gets "told" to open and close by the ECM.
ECM - Engine Control Module (computer)
EVP - EGR Valve Position sensor (atop the EGR valve)
EVR - EGR Vacuum Regulator solenoid (inline with EGR vacuum supply)
Apologies for the incomplete info here but I am not at home and cannot reference wiring diagrams to tell you which wires (colors) to actually perform the checks on. I can look it up and post later.
Is your voltage check the output voltage from the +5VDC (VREF) power supply in the ECM or from the EVP BACK to the ECM? You should get really close to +5VDC from the VREF pin on the EVP. The concern is whether or not the return voltage (SIG RTN) FROM the EVP back to the ECM is within spec. Even fully closed, the return voltage FROM the EVP should not be the same as the voltage coming TO the EVP from the ECM.
The other thing to determine would be whether or not the EVR is actually working. The EVR gets "told" to open and close by the ECM.
ECM - Engine Control Module (computer)
EVP - EGR Valve Position sensor (atop the EGR valve)
EVR - EGR Vacuum Regulator solenoid (inline with EGR vacuum supply)
Apologies for the incomplete info here but I am not at home and cannot reference wiring diagrams to tell you which wires (colors) to actually perform the checks on. I can look it up and post later.
Okay, nice info. Yeah checked again and KOEO VREF is 4.99V on the nose and EVP Signal is .49V so this looks correct.
You say voltage increase as vacuum decreases. At an idle I'll read ~0.5V at the EVP SIG and as I increase engine RPM the voltage will increase, never over 5V though.
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My Haynes says there should be ~5K ohms between the VREF and the EVP Signal under no vacuum and ~100 ohms under 20in.Hg. I'm reading ~3.4K ohms under no vacuum and ~730 ohms under 20 in.Hg. (In the text it says use 10 in.Hg. and in the caption under the picture it says to use 20 in.Hg., both pressures gave the same reading of ~730 in.Hg. Typo I guess) So can I rule the EVP sensor as faulty?
Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
Not voltage, resistance increases which will bring the voltage DOWN from the maximum +5VDC coming from the ECM and as long as the voltage reading does not exceed +0.67VDC during the KOER test (@ idle), the EVP is fine.
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My scanner explains it as "Defective EGR pressure transducer sensor", does it mean the EVP?
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Lead Driver
Joined: Sep 2002
Posts: 9,182
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From: Gateway to the West
There is no DPFE (Differential Pressure Feedback) sensor in a Bronco prior to 1996 when OBD-II (which has slightly different protocol and produces entirely different fault codes) was mandated.
Code 34 SHOULD only be generated when the voltage coming BACK to the ECM from the sensor is higher than it should be when the valve is fully closed. The highest reading fully closed is +0.67VDC as we discussed. If Code 34 continues to be generated in spite of the voltage not exceeding +0.67VDC during the KOER test, the problem lies within the ECM itself.
One other potential issue would be the EVR. If it is stuck open and the EGR valve is getting vacuum all the time, then the Code will trigger simply because there are times when the EGR should NOT be open. For example, at idle there should be no vacuum at the EGR valve. The EVR should be "off" thus leaving the vacuum line to the EGR valve closed. EGR should not be open under acceleration but open at cruising speeds or "part throttle" drive operations. Its really all up to the ECM to decide.
Code 34 SHOULD only be generated when the voltage coming BACK to the ECM from the sensor is higher than it should be when the valve is fully closed. The highest reading fully closed is +0.67VDC as we discussed. If Code 34 continues to be generated in spite of the voltage not exceeding +0.67VDC during the KOER test, the problem lies within the ECM itself.
One other potential issue would be the EVR. If it is stuck open and the EGR valve is getting vacuum all the time, then the Code will trigger simply because there are times when the EGR should NOT be open. For example, at idle there should be no vacuum at the EGR valve. The EVR should be "off" thus leaving the vacuum line to the EGR valve closed. EGR should not be open under acceleration but open at cruising speeds or "part throttle" drive operations. Its really all up to the ECM to decide.
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Well I've tried two ECM's with the same program and three different EGR valves and sensors atop the valve. All came with the same result of code 34 with the codes and memory being erased. The O2 sensor was bad on the Bronco, for how long I don't know, but do you think it could have comprimised the CAT? Plugging it up. The top end power of the Bronco seems to lack and seems to struggle on moderate to hard acceleration.
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Tonight is my last night of work, and then I have off for four days for Turkey break. During break I'm gonna punch the CAT out and see what that does. I'll give you guys an update.
On a lighter note, my Dad just picked up a 2007 F150!
Only 45K miles on'er. He loves it, gives me some breathing room to get the Bronco straightened out.
On a lighter note, my Dad just picked up a 2007 F150!
Only 45K miles on'er. He loves it, gives me some breathing room to get the Bronco straightened out.
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