1994 Bronco 5.0 XLT E4OD 4x4

I have been chasing down code 334 for sometime now, with no results. The code first appeared after replacing all the plastic vacuum lines with hoses. While removing the plastic vacuum lines I found that someone had put a T in the black line to the TAB & TAD and hooked the EVP up there. I also found that the EGR port on the throttle body was completely blocked by carbon build up. I cleaned the throttle body, and replaced the IACV & EGR. I have cleared the codes, run multiple KOEO and KOER tests, and tested different vacuum hose configurations. I replaced the EVP. Still code 334. I don't think it is relevant but I have also gotten a knock sensor code intermittently during this same time. I checked the ground, and vacuum tested the EGR. This is where I have found something that may be indicative of the problem. The EGR stumbles the engine with 5 in vacuum, yet the line from the EVP to the EGR does nothing but sit at about 2 in, even when I do a snap throttle to 2,500 rpm. I put the old EVP back on and got the exact same results. I suppose the new part could have the same problem as my old one, but I am not sure.

Has anyone dealt with a lacking of vacuum spike going to the EGR when doing a snap throttle to 2,500 rpm?

 

Code 334: EVP circuit above the closed limit of 0.67 volts

Have you measured the EVP output with the Key On Engine Off? Same for Key On Engine Running?


The computer is not supposed to turn on the EGR when snapping the throttle as you stated. It's only applied with a warm engine under cruise/light load conditions.

 

Thanks, That is the test I plan to do next. Is there a detailed procedure description for this and testing the EVP circuit?

 

EGR Valve Position sensor

 

You wouldn't happen to have a part number for the knock sensor?

Some parts stores don't even list the part. Others show multiple universal units. I will pull it and find a universal, or use the one from my F-150, as a last resort.

 

Knock sensor is pretty much unobtanium these days. No one makes them. You MAY find a NOS buried somewhere.

In reality there may be nothing wrong with yours. During the Goose Test the computer is looking for spark knock. If the weather is cool, timing set to spec or below, you are running high octane fuel or high elevation you may not generate any ping. This is the least of your worries right now.

I'll have to dig up some old posts to find a part number, but I do not think you need to go down this path IMHO.

 

I have already decided that a Bosch universal knock sensor would be my best replacement, but I would only go that route if swapping sensors with my F-150 fixed the problem.

Your speculation on weather is dead on, and also the reason I have not done anything with it lately. The Knock error code only comes up on the cold days. My timing is dead on spec until I get everything correct.

Could an ECM problem cause this? I ask this because I was going to see if you had another procedure for testing the ECM side of things. It seems possible with 2 sensors giving the same partial results.

 

After swapping the EVP with my F-150 code 559 cleared. After swapping the EGR code 334 cleared. This indicates the new EVP and EGR were both faulty. I will get replacement new ones. Now all I have left are the air lines in the dash. Does anyone have a detailed testing procedure for those?

I am curious about the location of the supply port for the EVP. I have been using the below diagram, which shows the source being about halfway between the manifold and the canister. Would this location make any difference in operation of the EVP when compared to using a manifold port as a source?

 

I am not aware that running direct manifold vacuum to the EVR will make a difference in operation. The vacuum reservoir has an internal check valve to provide vacuum to the ported side that goes to the TAB/TAD I believe.

This is used under low/no vacuum conditions. In this scenario the EGR valve should be closed anyway.

 

I have not noticed a difference, but I always figure there has to be a reason Ford would spend the extra money to run a separate custom formed plastic supply line around the engine. Couldn't the state of the check valve, basically the vacuum available in the canister, affect the amount of vacuum the EVR gets if they share such a long supply line. Even the size of that supply line could have significance if this is affecting anything. Could this be a safety to ensure the EGR closes if anything happens to the canister vacuum?

I was surprised to find my F-150 had the same type of T mod to the air lines as the bronco to connect the EVR to the same supply line as the TAB & TAD. I have owned this truck for over 10 years, and I can not remember doing this. Luckily I purchased enough vacuum hose to do both engines, only because it only came in 50 ft rolls.

 

I'm sure there was a reason, but what that might be is beyond me.

 

While replacing the plastic vacuum hoses I decided to try using the supply line for the TAB and TAD to supply the EVR on my F-150 because I knew it had no issues. Everything was fine until interstate driving after warm up. She was downshifting, and not giving me the power. I switched back to direct manifold supply and everything is fine. I just don't get how it worked so well hooked up the wrong way for so long. Maybe the plastic hoses were so cracked it didn't make a difference, yet I always get code 111 on KOEO and KOER both before and after the change.

 

mine also had that T you speak of, just how it was ran i guess.