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Discussion Starter #1
[RESOLVED] code 334 & 172 - EGR closed voltage higher than expected

Guys, I really need help with an incredibly stubborn Code 172 & 334.
I suspect the 172 is just a symptom of the code 334.

1994 Bronco
5.8L Windsor
E40D auto
192k miles
No mods that I know of.
Just bought it from a car lot a few weeks ago, issue has been present from day one.


Symptoms I get:

Runs smooth till it warms up.
Then when I stop at a light, the idle might suddenly drop from ~1k down to ~500 RPM and stumble.
Then pop back up to ~1k for a moment, then drop to ~500 again. And occasionally dies.
When this happens, sometimes the tranny will suddenly start shifting at really high RPM's with whiplash effect.


Things I've replaced in the last two weeks:

-EGR Vacuum Regulator Solenoid
-Coolant Temperature Sensor
-Idle Air Control Valve
-Throttle Position Sensor
-Fuel Pressure Regulator
-ACCEL Supercoil
-ACCEL Distributor Cap
-Ford Racing Spark Plug Set
-02 Sensor
-EGR Valve Position Sensor
-Replaced all vacuum hoses
-Cleaned PCV Valve
-Cleaned Throttle Body


Troubleshooting steps I've taken so far:

-Plugged Vacuum tester into EVR top line going to EGR and it held vacuum.
-Plugged Vacuum tester into EVR bottom line going to solenoids and it held vacuum.
-Applied vacuum to EGR while engine was running and the diaphragm moved and engine idle changed.
-EVR 12V pin shows -12V on my multimeter.
-Shorted EVR's pin 33 to ground while engine running and the engine died.
-Applied vacuum to vacuum canister AMP with MAN disconnected. It holds vacuum fine.
-When I do the KOER code test, the EGR does not move.
-Hooking a vacuum gauge inline with canister AMP shows "green" levels of vacuum (good).
-EVP shows 5v at pins VREF and SIG RTN.
-EVP shows ~3700 ohms at pins VREF and EVP and it goes down to ~350 when I apply 10hg vacuum to EGR.
-Disconnected IAC. Applied vacuum to EGR and engine RPM's stumbled as expected.
-Put Vacuum tester inline at EGR and raised engine RPM's, the vacuum does not register anything at all.
-I have yet to see the EGR move except for when I manually apply vacuum to it.

I'm sure I've forgotten a few things.
Any and all help would be appreciated!
If there are any sensors I should try replacing, then I can do that too.
 

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Am I reading it wrong or is Code 172 an Oxygen sensor code?
Have you replaced the O2 sensor? Odds are it's likely the original.
Rock Auto has the OEM replacement Bosch 15717 for $26 + shipping.

I'm fairly new to Ford OBD-I - but I know with OBD2 and GM OBD1 - we always wanted to take care of O2 sensor codes before addressing anything else.

Also it appears the code 334 can involve the EGR Valve position sensor (EVP).

http://www.fuelinjectedford.com/page35.html
 

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From what I understand if you use a jumper wire to ground the ground signal wire from the ecm to the evp sensor you are only supposed to do so very briefly...I wouldn’t do it at all...not with the wire we are discussing still connected to the ecm. Maybe didn’t hurt anything but putting a possible red flag there to remember. If all your testing is repeatable and verifiably correct you should not be having this code at all. Will think further on this when I get more time. If you only had a warm engine stumble I would say look at testing or replacing the coolant temp sensor located above the thermostat housing...these primitive computers don’t know when that sensor is bad. In your case solving the 334 code looks like a priority, but if you know and gor certain don’t have a leaking egr valve then plug the vacuum to it off and drive it. If you still have the same symptoms (disregarding the code), then go straight to the coolant sensor next. A pain to change but cheap. I can point you toward a way to do it without the special socket....
 

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Also, regarding a warm engine stumble on a fuel injected engine it is important to remember a couple of simple rules: a rich fuel/air mixture like you should have when the engine is cold will be easy for the ignition to light on fire. As the engine warms (if the coolant sensor is working right), the injector pulse duration shortens and the mixture in the combustion chambers becomes much leaner and therefore harder to light. Ignition weaknesses or clogged fuel injectors will result in stumble and funky idle...Yes I’ve had too much espresso!!😎
 

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Code 334 indicates the closed EGR signal value is too high (>.67 VDC). This could be caused by a EGR valve that is not fully seated. This can be caused enough build up to prevent the valve from fully seating. This can also allow unmetered air into the intake which in turns causes a lean condition/code (172).
 

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Yo Eddie,
From your well-defined tests and observations I believe you tested according to Ford, SEATTLE FSB, etc.
But, I will need help from others aside from my much-better-half to confirm all of you test results.

DTC 334 EGR (EVP) closed valve voltage higher than expected; "...Prior to re-installing see if you can blow air through the flange side of the EGR by mouth. ..."
Source: by rla2005

A defective EGR valve will not open or close when vacuum is applied. Find out if EGR intake and exhaust passages are plugged with carbon deposits.
When you removed the valve wase the orifice coked up w/oil residue? May need to use See Foam or use wire coat hanger and try to loosen up all the deposits and remove with a vacuum cleaner.

See How to Seafoam by Xris @ https://www.fullsizebronco.com/forum/23-technical-write-ups/43682-how-sea-foam.html

For posterity;

by Ford
 

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Discussion Starter #7
Weird, I forgot to add a subscription to my own thread for email alerts.

Yep, 02 Sensor has been replaced. As has Coolant Temp Sensor.


Code 334 indicates the closed EGR signal value is too high (>.67 VDC). This could be caused by a EGR valve that is not fully seated.
Seriously? I thought it meant the EGR was not opening under load.
But you're saying it's actually talking about the EGR not being completely closed, like it's supposed to be at idle?
Wow, maybe I should try changing the EGR then since that has not been replaced (by me).
It looks brand spanking shiny new inside/out so there is no carbon buildup but maybe it's defective.
I assumed it was fine because vacuum manually applied will make it open.

Why not. I already seafoamed everything else already. LOL
I'll try to seafoam the vacuum system tonight. :)


Thanks folks.
 

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Discussion Starter #9
Since I'm apparently not driving to work tomorrow (thank you Uber for being there), I think I may go ahead and rip my Intake Manifold off and give it a good scrubbing.
It's not caked up with carbon but it does have a good layer of carbon around all inside walls.
EGR valve port is same. Just a layer on the walls. Nothing interfering with flow though.

Gonna go research removal & cleanup now.

EDIT:
n/m I'm not going to complicate things any further.
Going to fix my issue before I potentially dig myself into a deeper hole.
 

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I’m pretty sure you can drive it with the diaphragm broken, it won’t open but should stay closed just fine...
 

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Discussion Starter #11
I’m pretty sure you can drive it with the diaphragm broken, it won’t open but should stay closed just fine...
I actually did just that. 35 miles round trip just to get one that was in stock.

No change in problem.
Brand new EGR Valve and I still get code 172 & 334 during KOER test.
ugh

Too late to do anything else tonight.
 

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I actually did just that. 35 miles round trip just to get one that was in stock.

No change in problem.
Brand new EGR Valve and I still get code 172 & 334 during KOER test.
ugh

Too late to do anything else tonight.
Don’t let it worry your sleep. This WILL be solved...
 

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Since you inherited this issue someone may have replaced the EVP sensor before. We have seen the rod on the sensor too long from the manufacturer. This will cause the closed EGR signal (via the EVP) to be above specification then trigger code 334.


Assuming you are getting Code 334 in KOER only? Another test is disconnect the vacuum from the EGR valve then re-run the KOER tests. If so, that points to vacuum getting to the EGR valve at idle, when there should be zero.
 

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Discussion Starter #14
Assuming you are getting Code 334 in KOER only?
I get 334 in KOEO also, even after clearing the codes.



Another test is disconnect the vacuum from the EGR valve then re-run the KOER tests. If so, that points to vacuum getting to the EGR valve at idle, when there should be zero.
Sorry, I didn't understand?


Ssince you inherited this issue someone may have replaced the EVP sensor before. We have seen the rod on the sensor too long from the manufacturer. This will cause the closed EGR signal (via the EVP) to be above specification then trigger code 334.
Yeah, the Bronco came with a shiny new looking EVP.
So now I've got two EVP's, neither are Motorcraft/Ford.
And no way to get a Motorcraft one till Friday.

I'm thinking of shaving off a bit of the pintle one one of these and testing that.
 

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Discussion Starter #16
I cannot believe it, but you were RIGHT.
That stupid freakin dorky tater tot silly EVP.
Both the old brand-new one AND the new-new one that I bought, were DEFECTIVE.

I shaved a tiny bit off the end of the pintle.
Put it on the EGR.
Ran the OBD1 test.
No codes.
No codes.
NO CODES.
Just 111 I loves you. 111 you are free. 111 **** the EGR. 111 time to move on now.

I put the spare old-new EVP on my bench grinder and took off as much metal as you can see in the pics below.

3rd pic is where it was before I touched it.
2nd pic is how much metal I removed from it.

Installed it.
And all is sooooo good.

I mean, pending drive test and all that.
But I'm going to buy the Motorcraft EVP anyways.
Should be here on Monday.

LIFE IS GOOOOOOD AGAINnnnnnnn
 

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Glad to see you got this one whipped. I was clued into the EVP issue with aftermarket pieces from a member on another forum. Aggravating when new parts cause issues. Shaving down the actuator/pintle is the "fix" when you have verified everything else is good.
 

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Discussion Starter #20
All is not yet well, unfortunately.
The 334 & 172 codes seem to be gone forever.

But the driveability issues continue and I have a new code now.
Code 452 Computer detected an error in the VSS or PSOM signal

So the symptoms continue to be hard, high RPM shifts AND the idle drops down to ~500 with occasional stall.

I'd already replaced the IAC earlier.
So yesterday I replaced the VSS with a Motorcraft unit.
No change in the problem, so I tried unplugging the VSS and the issue continued.
Then I plugged VSS back in and cleared the KOEO codes.
And the issue went away. It ran perfect.
I let the engine cool off, then I went for another drive and after it warmed up, the issue returned along with the 452 code.

So yeah, I'll be researching PSOM replacement and will start a new thread if needed.
Just wanted to update this one with the results.
 
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