334 is EGR- which could explain alot of yer problem

Code 334 - Ford Truck Enthusiasts Forums

1987 - 1996 F150 & Larger F-Series Trucks - Code 334 - The Actron code reader said I have a 334 KOEO. Looks like a problem with the EGR... 334: EGR Valve Position (EVP) sensor – signal voltage higher than expected (closed valve position). I got a 334 for the CM too. The truck idle is smooth when...

www.ford-trucks.com

 

I was really hoping I could wait till MD to go down this road lol. I took the bronco out (after it had sat for a couple hours), she drove just like it normally does, no popping/hesitations. This may be a dumb question - but would the EGR be sensitive to heat (in terms of it'll work/not work)? I get that it's supposed to pass exhaust back to help w/emissions but other than that I am clueless.

I have a cheap DVM w/me so I'll have to run through the above listed thread in the AM. (daylight).

 

The EGR doesn't kick in until the truck gets warm. Pull the vacuum hose and make real sure it is good, would be nice if that is the problem! The EGR is there to try to keep your exhaust cooler to reduce NOx (part of smog). If it has a problem, the EEC retards the ignition timing to try to keep the cylinder temperature down.

 

Yo java9,
As broncosarge77 advised.

Testing; "...There shouldn't be any vacuum at the EGR valve at idle or any time your ass is under the hood fiddling with it, to put it plainly, except for perhaps a very light residual vacuum from the EVR. Check ALL of your vacuum lines FIRST, and the vacuum reservoir for leaks..."
Source: by SigEpBlue (Steve) at FSB

If your emission vacuum reservoir is metal, inspect underside for rusted sections.

I believe you referenced, "Replace Plastic Vacuum Hoses with Rubber" by booba5185 @ Replace Plastic Vacuum Hoses with Rubber
Excerpt;

 

I believe that is the post (lines). I'll check the can this morning. I do remember rust/can't remember if I replaced it or not back then.

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@Bruners4 is in that area, might be able to help in some way. Im about 3 hours south of Lincoln, but im no good with electrical gremlins.

 

She fired up and drove fine last night around town and a very little hwy. I have an easy day today (5hrs ish) headed to MO. I'm going to do some quick poking around this morning voltage wise.

I'll have to see if any of the stores loan out vacuum test tools. (All my stuff was delivered to MD yesterday so I'm running with what I could fit in a tool box and a crate of fluids/belt/fuel filter. (Better to have and not need... I'm kicking my self for not finding a spot for the damn vacuum tester lol) figured with my new lines that wouldn't be an issue [emoji25]

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The EGR code indicates it could be hanging open which will cause a lot of the running issues described. When it's back to running well, I would try disconnecting and capping the vacuum line to the EGR valve. Generally the EEC can manage a never opening EGR, but when it's unexpectedly open it gets lost.

 

Sorry I'm a little late to respond. The only other thing that I can think of that heat effects is the Ignition module. The heat paste dries up and doesn't allow for the module to transfer the heat away from it. I like to clean the old paste off and apply new heat transfer grease one in a while.
As I'm thinking about the EGR and low vacuum, I could see that an EGR valve that isn't completely closed would effect the engine vacuum at lower speeds. I've always wondered how the engine would react if the only thing that a person did was to block off the exhaust from the EGR valve. Would the sensor detect that there wasn't any pressure on the exhaust side and throw an error code?

 

I've always wondered how the engine would react if the only thing that a person did was to block off the exhaust from the EGR valve. Would the sensor detect that there wasn't any pressure on the exhaust side and throw an error code?

On my 94 351, I put headers on with no egr provision. I left the egr hooked up, and the tube for it was hacked off right next to a header pipe. Never had any drivability issues with it. I no longer had an O2 sensor either, and though I had a couple codes, I drove it for years like that.

 

Yesterday did not go as planned lol. The morning started off good, even had some construction stop and go and she did fine. 4 hrs. later I'm checking out possible camp sites (1K rpm ~15 -20 mph for maybe 25 mins). I decide to go into town and get some supplies. TRIED to pull onto the divided hwy and she sputters and bucks like before. Starts misfiring (popping) like crazy this time though. Pulled off to side and started looking around. Nothing jumps out for the sudden increase in backfiring.

After sitting for 1/2 hr. or so, I try again and eventually make it into town and park at a Walmart while looking for an auto parts store. (Turns out Oriellys doesn't have a hand vacuum tool for loan). I only made it by pressing the gas until it starts to bog down, letting off and repeating until it finally got to highway speed and drove normal again)

Decided to press all night to my current spot in MS as if she dies, I need to be as close to my first destination as possible. After sitting for a while in the parking lot, she finally fired up and then I had to baby it through the city again.

I finally get on the highway and drive the 6.5 hrs. (She did great all night, temps where in the 70s vs. 80's & 90s and even had a bit of showers).

Found an auto zone that loans the tool I need (have it now, after I clean up I'm going to run all the vacuum test y'all suggested, I'm here for 2 days as part of my original plan so now I have some time.) I did check voltage yesterday and it was 4.97 on the EGR sensor sig.

One question I have and can't stop coming back to... it will not go over 2400 RPMs (load or not), if I mash the pedal the rpms drop to zero though the vehicle still accelerates. Can this be connected to the EGR as well?

**O I forgot to ask - during all of the bucking and issues, never once did my CEL come on. Why would that be? (It does lit up when your first turn the key so I know the bulb is good lol)

hope that makes sense, this is on my cell as I don't feel like unpacking everything to get to my computer at the moment.

 

I have a 1996 5.8l. I had a similar issue, on the highway, during summer, on a trip, in the heat, seemed to be at certain speeds and worse uphill, but sometimes in town it seemed fine except sometimes accelerating from a stop. It had been a long time since a did a tune up and I was also a state away from home.
I had to borrow tools from autozone. I did quick stuff first, coil, cap and rotor. I thought it was fine on the 5 min test drive, but it really wasnt. I started changing the spark plugs and the wires. I broke a wire on the passenger side, so I can't say if it was the wires or the plugs, but after that, I was all good. I think you should recheck your spark plugs and wires. It might be that simple. I also had a similar problem with egr codes. I ended up finding the leak 2 years later after it got really loud. It was leaking from my brake booster. There was always a rust spot running down the underside of it, but looked normal to me. lol. If you have problems with rust, the starter wire to my starter relay, has a plug boot type of connector on it and was filled with rust, but I never noticed from just looking at it on the outside.

 

Yo java9,
The firing order for ALL 5.8 EFI Broncos is 1-3-7-2-6-5-4-8.
On these vehicles the #1 and #3, or #5 and #6 spark plug wires must be separated to eliminate the possibility of an induction crossfire. To eliminate the possibility of the coil wire becoming disconnected, route the coil wire under the spark plug wires at the distributor cap. Distributor rotation: Counterclockwise
Ford

 

I learned that during the initial tune up lol back in 2017/2018. Can't remember what wires they were, but they definitely did not like to be near each other. This and the day gap had me chasing my tail for a day. (Mostly the gap as I had checked them numerous times before putting them in.)

 

Test from this morning -
EGR holds vacuum and engine stumbles when applying.
34K and slightly over 1K for ohm readings. Can't figure out how to do the .67 volt check (tried searching and can't find the how to) Links listed above in first response redirects to links no longer valid.

Thoughts, where to next? (I do need to Google the IAC mentioned above and let my engine cool down to double check plugs and wires. (But why only low end acceleration and not all the time? Only asking because the first time I tried the tune up, the gap messed up (though I checked it multiple times lol) and the engine ran like absolute crap the entire day and half it took me to recheck the gap.

 

I checked the IAC...

Voltage at connector is 11.8v

Resistance:
Pin to pin: 10.3
Pin to body: open


Also, was finally able to do a full KOER and the only code besides the 334 is 313.
----Thermactor air system/air not bypassed during self-test....

So what did I forget to turn on/switch? I got the WOT and OD right this time lol.

 

EVR testing

Won't hold a vacuum regardless of 12v applied or not. (Though this may because of my janky connection to the battery lol) however on top of that, resistance is shorted when testing at the terminal.

So unless I messed something up 🤔🙄, I'm looking at a new EVR correct?


*Sorry to rapid fire today. Once I get to AL, I'll be on lockdown until training is over. So I should be relatively quiet as I can't run out and get things lol. Thanks Covid....

 

Yo j,

TAD Solenoid & TAB Solenoid pic by Seattle FSB
▪
TAD Solenoid & TAB Solenoid Test; .Key off. Disconnect both Solenoid connectors to measure both resistances. Each resistance should be between around 50 to 100 ohms.

DTC 313 indicates that Secondary Air is not being bypassed when requested.
Possible causes:
Visually inspect vacuum lines for disconnects in the AIR system.
Visually inspect for proper vacuum line routing. Refer to VECI decal atop radiator cover.
Visually inspect Air Pump for broken or loose Air Pump Belt.
Were any problems found?
Yes SERVICE as necessary. RERUN Quick Test.
No GO to KC2 .

KC2 CHECK AIR VACUUM LINES
Carefully check AIR vacuum lines;
From TAB Solenoid to TAB Valve.
From TAD Solenoid to TAD Valve.
From Manifold Vacuum TREE to TAB/TAD solenoids.
Check for obstructions, cracks, kinks, and leaks, etc.
Are vacuum lines in good condition?


For DTC 313:
No, repair.
Yes GO to KC4 .
No SERVICE as necessary. RERUN Quick Test.

KC4 ATTEMPT TO ELIMINATE DTC 313
Disconnect vacuum line on TAB Valve and cap vacuum line.
Key off.
Repeat Engine Running Self-Test and record DTCs.
Is DTC 313 present?
Yes EEC-IV system OK. RECONNECT vacuum line. .
No GO to KC5 .

KC5 CHECK TAB & TAD SOLENOIDS ELECTRICAL OPERATION:
DVOM on 20 volt scale.
Disconnect TAB Solenoid.
Connect DVOM positive test lead to VPWR circuit and negative test lead to TAB circuit of TAB vehicle harness connector. miesk5 note; see below Wiring Diagram; VREF is the Red Wire.

Wiring diagram by Mikey350

While observing DVOM, depress and release the throttle several times (to cycle output On and Off).
Repeat for the TAD Solenoid.
Does each solenoid circuit cycle 0.5 volt or greater?
Yes GO to KC6 .
No REMOVE jumper. GO to KC10 .

KC6 CHECK TAB/TAD SOLENOIDS FOR INTERNAL VACUUM LEAKS:
Reconnect TAD/TAB harness connector.
Vacuum pump connected to the supply port and vacuum gauge connected to the output port of one solenoid. miesk5 note; supply is from vacuum tank.
Apply 15 in-Hg vacuum & observe gauge.
Repeat steps above for the other solenoid.
Does vacuum gauge reading hold for each solenoid?
Yes GO to KC7 .
No REPLACE TAB/TAD Solenoids. RERUN Quick Test.

KC7 CHECK TAB/TAD SOLENOIDS FOR VACUUM CYCLING:
Install vacuum pump to the TAB Solenoid vacuum supply port and install a vacuum gauge to the TAB output port.
Apply 15 in-Hg vacuum.
While cycling outputs On and Off (by depressing and releasing throttle), observe the vacuum gauge at the output.
Note: Re-apply vacuum between cycles.

Repeat for TAD Solenoid. Connect vacuum pump to the TAD solenoid vacuum supply port and connect a vacuum gauge to the TAD output port.
Cycle output on and off.
Does each solenoid cycle vacuum output on and off?
Yes RECONNECT vacuum hoses.
No REPLACE TAB/TAD Solenoid assembly.
RERUN Quick Test

7p

 

I hope you figure out the stalling problem above 2500. As for the AC problem throwing the air up to defrost, that is the white vacuum line under the hood which is buried in the harness that the AC fan motor connector comes from. What you do there is peel back the harness till you see good white vacuum line. Then cut it. You can do this at the auto parts store. Then go find a rubber vacuum line that will perfectly fit over the white line. Not sure of the size. Then slip the new rubber line over the good cut end of the white line in the harness. Then run it up to the vacuum motor by the passenger side windshield. Remove the little rubber connector the white line plugs into and the new rubber line should fit snugly over the metal nipple on the vacuum motor. That will usually solve your AC vent register shifting problem. If it does not, then the problem lies in the vacuum reservoir located on the Evaporator box. Its a small one that is molded in. If it is bad, you will have to scavenge a different style of vacuum reservoir from a junk yard, ebay, or parts store and use it.

 

I hope you figure out the stalling problem above 2500. As for the AC problem throwing the air up to defrost, that is the white vacuum line under the hood which is buried in the harness that the AC fan motor connector comes from. What you do there is peel back the harness till you see good white vacuum line. Then cut it. You can do this at the auto parts store. Then go find a rubber vacuum line that will perfectly fit over the white line. Not sure of the size. Then slip the new rubber line over the good cut end of the white line in the harness. Then run it up to the vacuum motor by the passenger side windshield. Remove the little rubber connector the white line plugs into and the new rubber line should fit snugly over the metal nipple on the vacuum motor. That will usually solve your AC vent register shifting problem. If it does not, then the problem lies in the vacuum reservoir located on the Evaporator box. Its a small one that is molded in. If it is bad, you will have to scavenge a different style of vacuum reservoir from a junk yard, ebay, or parts store and use it.
View attachment 162799

I replaced that line when I first bought her. It's what drove me to swap all the other lines as well. I barely moved it and it crumbled in my hand lol. I'll have to check the reservoir though.

- side note, I had enough of the southern heat this morning and took the risk of running the AC while in town....knock on wood it's been good so far. The vent thing is super random and I notice it mostly when trying to accelerate. (Regardless of AC or heat or just Vent).


Thank you for the ecm tip as well, once I'm safely in AL at training I will poke around with that on the weekend, depending on how much work they try to give me lol.

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Another thing to consider, once you reach your final destination, it wouldnt be a bad idea to pull the EEC main computer and check it for burnt out capacitors. It happens all the time with these older trucks. They were never designed to last 30+ years and occasionally need replacement. This same thing is a big cause of HARD shifting when the capacitors in the PSOM go bad.

 

Just to cover the basics related to your rpm limitations, how is your fuel filter? I've seen partially clogged filters cause issues at higher rpms & under acceleration. Those times that demand more fuel. The other symptom that might point towards a fuel filter is that it seems to recover after a short rest. It almost seems like the crud falls away once the flow is stopped. Only to be sucked back up again after awhile on the road. I suppose a blocked sock in the tank might do the same thing, but the filter is where I've seen it behave that way.

While you're thinking about filters, how is the air filter?

 

Fuel filter was changed fall if 19 ( I do have a spare w/me so I might just throw that in). Air filter is one of those k/n aftermarket things the PO put on. Doesn't look caked. I'll look at that again though.



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The vent issue is due to a bad check valve, the one in my bronco was intermitently acting up.

Good luck with everything else. This page helped me more than ANY of my factory service manuals, and I have all of them for my year.

How To Test The Ford EGR Valve, EGR Vacuum Solenoid, DPFE Sensor

4.6L, 5.4L Ford F150, F250, And F350 Pickups Index of Articles

easyautodiagnostics.com

 

What check valve are you referring too? The reservoir that JOwens mentioned or is there another item I need to look for?

 

Made it to AL. I didn't have any issues today, but it was also only 4 hr. ish drive. I did make two stops within the city and she fired up and drove w/out issues both times. Only thing done besides disconnecting and reconnecting things was replacing the EVR solenoid. So I doubt she's fixed. I'll find out in ~26 days when I head to MD.

Miesk5 - followed the TAB/TAD as far as I could. (didn't have another person to help rev while watching DVM. Everything up to that point passed though. (Good vacuum and good resistance values ~80 for each). When I get to MD I'll have the wife give me a hand so I can finish the rest of the check.

I will say though, I'm thinking my problem is the fact I can't go above 2400 RPMs, I watched my engine sit around "max" for 3hrs, while pulsating around hills due to the rpm restriction.