Suddenly developed a miss
03-13-2016, 11:03 PM
#41
The fault responsible for these EGR codes could also cause a lean misfire and detonation. DTC 327 & 328 indicates the EGR valve (EVP) sensor signal is less than the minimum value of 0.2 volts. Because the EVP sensor is preloaded when attached to the EGR valve, a EGR failure causing the EVP sensor to lose preload may also set these codes. Also, the PCM will command the EVR to apply more vacuum to the EGR valve in order to see an EVP voltage change. The valve could be fully open (full EGR flow) with a faulty EVP showing a closed voltage. The MAP, EVP and TP sensor share the same VREF circuit BR/W - PCM pin 26. I would temporarily disconnect and plug the green vacuum line on the EGR valve and re-evaluate. You either have a faulty EGR valve and/or EVP, wiring or possibly PCM. I have seen leaking capacitors (even on my own truck) cause a host of driveability concerns and set random codes. These capacitors, like a battery, have a shelf life and only last so long. This might be something to look into especially with the random concerns that you've been having.
http://fullsizebronco.com/forum/23-t.../218407?page=1
http://sbftech.com/index.php/topic,15654.0.html
http://fullsizebronco.com/forum/23-t.../218407?page=1
http://sbftech.com/index.php/topic,15654.0.html
I Haven't said it enough, but I really appreciate all the help you guys have been!
03-14-2016, 09:33 PM
#42
I tested the EVP sensor and resistance was way high so I replaced the sensor and disconnected the battery. No change in shudder/missfire symptom. Ran out of daylight before I could do the other tests mentioned. I will try to finish them tomorrow.
03-15-2016, 07:40 AM
#44
03-15-2016, 08:21 AM
#45
Just drove it to work and I was able to make the shudder/missfire happen in 3rd gear as well. It just requires a higher throttle input than in 4th. I'd say it was about 50% throttle in 3rd @ 30-35mph is when it would miss, and about 25% throttle in 4th @ 40+mph.
If it's happening in 3rd gear as well, it has to be engine related.
If it's happening in 3rd gear as well, it has to be engine related.
03-15-2016, 09:35 PM
#46
I was able to do a few things today after work. I measured resistance of my plug wires and I cleaned the EGR valve.
The resistance of the distributor to ignition coil wire was 4.15 K ohms
Cylinder wires in K ohms:
1 - 4.37
2 - 5.84
3 - 6.28
4 - 6.65
5 - 4.47
6 - 5.74
7 - 6.90
8 - 7.44
I'm not sure what each wire is supposed to be exactly, but I know plug wire resistance is suppose to be so much per foot, and the higher resistance wires are the longer wires. The longer the wire, the higher the resistance. I didn't find any wires that seem unreasonable. So I don't think it's a plug wire issue.
I inspected the EGR valve and manually actuated the valve by sucking on a piece of vac line hatched to it. It moved freely and didn't seem to be sticking. I cleaned it thoroughly and re-installed with a new gasket.
Then I test drove the truck. Didn't make it very far because the motor started sounding very unsteady while idling. When I stopped at a stop sign I put it in park and blipped the throttle, and it hesitated before it reved, then when it the rpms came down it tried to die multiple times before maintaining a constant rpm. I could tell because the batt charge gauge and oil pressure gauge dipped with engine rpm flu cation. (Truck does not have a tach)
At this point I don't know what else to do other than remove the PCM and inspect the internals for a bad capacitor as previously mentioned.
Could a TPS issue cause an intermittent missfire? Before doing these few things this evening, I drove it for about 30 min and it would only missfire once in a while. I couldn't always duplicate it under the same conditions. It has to be electrical in some way being so intermittent.
The resistance of the distributor to ignition coil wire was 4.15 K ohms
Cylinder wires in K ohms:
1 - 4.37
2 - 5.84
3 - 6.28
4 - 6.65
5 - 4.47
6 - 5.74
7 - 6.90
8 - 7.44
I'm not sure what each wire is supposed to be exactly, but I know plug wire resistance is suppose to be so much per foot, and the higher resistance wires are the longer wires. The longer the wire, the higher the resistance. I didn't find any wires that seem unreasonable. So I don't think it's a plug wire issue.
I inspected the EGR valve and manually actuated the valve by sucking on a piece of vac line hatched to it. It moved freely and didn't seem to be sticking. I cleaned it thoroughly and re-installed with a new gasket.
Then I test drove the truck. Didn't make it very far because the motor started sounding very unsteady while idling. When I stopped at a stop sign I put it in park and blipped the throttle, and it hesitated before it reved, then when it the rpms came down it tried to die multiple times before maintaining a constant rpm. I could tell because the batt charge gauge and oil pressure gauge dipped with engine rpm flu cation. (Truck does not have a tach)
At this point I don't know what else to do other than remove the PCM and inspect the internals for a bad capacitor as previously mentioned.
Could a TPS issue cause an intermittent missfire? Before doing these few things this evening, I drove it for about 30 min and it would only missfire once in a while. I couldn't always duplicate it under the same conditions. It has to be electrical in some way being so intermittent.
03-15-2016, 10:30 PM
#47
Martin
03-15-2016, 10:53 PM
#48
Oh... I have not replaced that. I was unaware of it. My understanding was that the ECM performed those functions. I will definitely look into that! Thank you!
03-17-2016, 06:39 PM
#49
I replaced the TFI module yesterday after work and drove the truck about 40 miles. The missfire/shudder did not reoccur. I also drove it to work today and the symptom did not present its self. I'm going to keep an eye on it since it's been somewhat intermittent, but it's looking promising.
03-28-2016, 10:44 PM
#50
Senior Member
I replaced the TFI module yesterday after work and drove the truck about 40 miles. The missfire/shudder did not reoccur. I also drove it to work today and the symptom did not present its self. I'm going to keep an eye on it since it's been somewhat intermittent, but it's looking promising.