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Discussion Starter · #1 ·
Hey there y’all, having an EGR issue at the moment and looking for someone’s thoughts on it. I recently cut my muffler off and everything downstream from the high flow cat, because I was redoing it. I was driving it to work no issue and then at about 40 miles or so it starts to (what sounded like) misfiring. Rpm’s surging at idle, running very rich, loss of power… the whole ordeal haha. I drove a mile home and CEL came on, and had a IAT sensor issue. It was just unplugged, so I plugged it in cleared the codes and worked for another 40 miles. Now I’m getting an EGR code po402. I just cleaned the egr valve and no luck, though it was very dirty with carbon. My next thought is a lack of backpressure causing sensors to be thrown off based on the stock ECU sensor specs. Would this lack of back pressure cause this or what’s anyones thoughts? Thanks!
 

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Discussion Starter · #2 ·
Hey there y’all, having an EGR issue at the moment and looking for someone’s thoughts on it. I recently cut my muffler off and everything downstream from the high flow cat, because I was redoing it. I was driving it to work no issue and then at about 40 miles or so it starts to (what sounded like) misfiring. Rpm’s surging at idle, running very rich, loss of power… the whole ordeal haha. I drove a mile home and CEL came on, and had a IAT sensor issue. It was just unplugged, so I plugged it in cleared the codes and worked for another 40 miles. Now I’m getting an EGR code po402. I just cleaned the egr valve and no luck, though it was very dirty with carbon. My next thought is a lack of backpressure causing sensors to be thrown off based on the stock ECU sensor specs. Would this lack of back pressure cause this or what’s anyones thoughts? Thanks!
Just wanted to add it sounds basically cammed and the engines suspiciously vibrating at idle so maybe a misfire triggered that egr code because of almost no backpressure?
 

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1986 Eddie Bauer 5.0EFI AOD Full length headers Y pipe into single 3" Magnaflow 3" factory exit
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I could see there being issues caused by having it cut off like this, just by the o2 sensors possibly reading too much oxygen, and that could be messing with the fuel curves. Given I'm not an expert of the newer Broncos and multiple o2's of the 96, but aren't there post cat o2's on the 96??? I had bought my 96 new, so it had no issues when I had it, but the 86 I'm restoring now gave me all kinds of fits from the o2 sensor (single) being messed up, and the wiring being corroded & not getting a signal back to the computer.

I'd say get that exhaust back together and re-evaluate, until then you've introduced too much unknown into the system to possibly diognose anything properly. That may be all it is, but get the exhaust back on and report back.
 

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Discussion Starter · #6 ·
Gr
I could see there being issues caused by having it cut off like this, just by the o2 sensors possibly reading too much oxygen, and that could be messing with the fuel curves. Given I'm not an expert of the newer Broncos and multiple o2's of the 96, but aren't there post cat o2's on the 96??? I had bought my 96 new, so it had no issues when I had it, but the 86 I'm restoring now gave me all kinds of fits from the o2 sensor (single) being messed up, and the wiring being corroded & not getting a signal back to the computer.

I'd say get that exhaust back together and re-evaluate, until then you've introduced too much unknown into the system to possibly diognose anything properly. That may be all it is, but get the exhaust back on and report back.
Great advice, thanks. I have a post cat o2 sensor that has been fine with the exhaust on. Now that it’s off it could be giving bad readings. I have a new chambered Flowmaster that I’ll put on and see how that goes, as well as the rest of the exhaust.
 

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Yeah no problem, we're all just figuring it out as we go, im sure your ears will thank you once the exhaust has a muffler again, just be sure to put all the o2's back on in roughly the same areas they were when stock. Then you can pull codes again if its running funny, but something tells me it's just a bit confused on what to do with the downstream o2's off.
 

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Discussion Starter · #8 ·
Yeah no problem, we're all just figuring it out as we go, im sure your ears will thank you once the exhaust has a muffler again, just be sure to put all the o2's back on in roughly the same areas they were when stock. Then you can pull codes again if its running funny, but something tells me it's just a bit confused on what to do with the downstream o2's off.
Yeah I haven’t touched the sensors since I put the high flow on and haven’t had an issue. When I cut the exhaust off I didn’t touch that sensor at all. Just cut off where the muffler attaches to the cat and put that flex pipe on. So if that sensors confused possibly it’s compensating by giving the injectors too much fuel causing it to bog and maybe give that po402 egr code.
 

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I'll leave the 1996 sensor stuff to the guys with more knowledge there, cuz its out of my wheelhouse, but fear not, there's a ton of knowledge these guys have on how to make it all work, it's out of my league, but I'm sure someone will chime in on here to follow up more.

Just a bit confusing how your piecing the story together in multiple posts.
 

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Yo 351
Yo,
DTC P0402 - EGR Flow Excessive Detected; "... The EGR system is monitored for undesired EGR flow during idle. The EGR monitor looks at the DPF EGR signal at idle and compares it to the stored signal measured during key ON and engine OFF. The test fails when the signal at idle is greater than at key ON engine OFF by a calibrated amount.
Poss. Causes;
EGR valve stuck open
Plugged EGR vacuum regulator solenoid vent (EGR Vacuum Regulator (EVR); also called EGR Vacuum Solenoid)
Plugged EGR tube
Slow responding D.P.F. EGR sensor (Differential Pressure Feedback (DPFE) Sensor)
Damaged DPF EGR sensor
Improper vacuum hose connection
Plugged vacuum hoses
EGRVR circuit shorted to ground
Damaged EGR vacuum regulator solenoid (EVR)
Damaged PCM
A DPFEGR PID reading that is greater at idle than during key ON and engine OFF by 0.5 volt or a rough engine idle, may indicate a hard fault..."
The Ford EVTM will provide troubleshooting pin-point tests for all above

OBD Trouble Code P0402
Exhaust Gas Recirculation Flow Excessive Detected
What does the code mean? OBD-ii Code P0402 definition:
EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor (DPF). These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc. The P0402 code means that OBD detected an excessive amount of EGR.

Symptoms Sumptoms of OBD code P0402
You may notice drivability problems such as the engine may surge off idle. There may also be other symptoms.

Causes Causes of the OBD-II code P0402
A code P0402 most likely means one or more of the following has happened: The DPFE (differential pressure) sensor is faulty and needs to be replaced There is a blockage in the EGR (most likely carbon buildup) The EGR valve is faulty The EGR valve may not be opening due to a lack of vaccuum
miesk5 note, inspect the rubber hoses to the DPFE. Dealership sells them if needed. Do not use vacuum hoses.
It is common for people to replace the EGR valve, only to have the problem return. The most likely solution is to replace the DPFE sensor. Check the voltage at the DPFE sensor both at idle and when the EGR is open .
Source: by Ford

Hose part numbers; 1L3Z-9P761-AA - 1/4" for REF - Downstream hose (INTAKE); 1L3Z-9P761-BA - 5/16" for Upstream hose (EXHAUST); UPDATE DORMAN 46019 High Temperature DPFE Hoses OE#: 1L3Z9P761AA, 1L3Z9P761BA, "Contains both hoses for an easy repair..."


DPFE Testing & Vacuum/Voltage Parameters & pics on both older Aluminum & Newer Plastic Version; miesk5 Note, Tomco Figure 4 for Plastic Housing version, it shows +/- 0.25 volts; It should be 1.0 +/- .025 volts as desribed in the narrative and in Ford EVTM; "...Access DPFEGR PID (formerly DPFE) with a Scan Tool. PID voltage should be 0.2-1.3 volts..."
Source: by tomco-inc.com @ http://www.tomco-inc.com/Tech_Tips/ttt36.pdf

Location pic in a 96 5.8

Source: by edaminski

More yada, yada:
DTC PO402, PO401, P1400, & P1401; Usually the failure starts with an almost imperceptible surge while cruising. Gradually it develops into an annoying surge and then the check engine light comes on... Early versions of this part had an aluminum body - this plastic part is an update, and is much less failure prone that the early aluminum part..."...When OBD2 came along, the EPA said that we now have to be able to know if the EGR valve quits working and turn the check engine light on if it does. Ford chose to do this by installing a slight restriction in the tube that brings exhaust to the EGR valve. Now we all know from science class that when there is flow through an orfice, there is a pressure drop across it. So Ford installed a pressure sensor across the orfice - when there is flow because the EGR valve opened, the pressure sensor senses the flow and tells the PCM the system is working. That's why they call it a Differential Pressure Feedback EGR Sensor! Now, what do you think happens when you run hot exhaust gas into a little electronic sensor? It does not last too long.."
 
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