Ok for the last few months my engine has been running poorly. I've been trying to figure it out, but havn't yet.

The engine is basically stock, cept for exhaust. I took out my MSD 6a and my MAF conversion kit, put the SD back in.

I am getting codes 172 and 334 out of the computer.

The engine has very poor power (I have to go up hills in 3rd at 40-45 when I used to be able to make them in 5th at only 1500 rpm).

The engine will puff smoke out the exhaust between shifts when accelerating hard (running rich).

Basically it runs ok, starts all the tme, but it just isnt burning fuel correctly. The fuel delivery system is fine, the EGR was tested and is ok, the 02 sensor was tested and its ok. It is definitely an ignition problem. I've changed the plugs/wires/cap/rotor recently, and the coil is new. The wires going to the coil are only about 5-6 inches long before it goes into the main wiring harness and I can't follow it further, but they are not corroded.

One day my truck wouldn't start, and I unplugged my MSD 6a and plugged the coil into the stock harness like it was originally and it started. After that my tach started flickering on me and my MSD doesn't work (I plugged it back in later on and it still doesn't work, getting power to it though).

My tach will follow the engine's RPM, but say if I floor it and let the RPMs come up, after like 3k the needle will push ahead of the actual engine RPM, as much as 500-800 rpm. One time I let the engine RPMs come way up to about 4800-5k and the tach was showing almost 6k so I know it's not right. Also, if i'm crusing along the needle will flicker up and down about 50 rpm, and it'll do the same at idle. The engine is not doing this or I'd feel it/hear it in the exhaust, so the tach is not flickering w/ the engine. The tach is working fine other then those two issues, and I know for a fact that it isn't a problem with the tach.

I was told maybe the pip/hall effect sensor in the distributor or a short in the TFI module. Any other ideas?

 

sounds like you are havin some of the same problems that i am havin, but seems like mine is wanting to skip, a little at idle, and if it gets warm, if i floor it, it will spit and sputter so hard it will throw you back and forth, and i have done the same things that you have done, changed everything in ignition, and rebuilt carb, the only things that i havent changed are the ignition box on the fender, and the module in the bottom of the distributor. mine is runnin rich a little as well, and my tach will jump quite a bit if it starts skippin, i replaced the coil, and it stopped for a while, and now it is doin it again, have you figured out what the codes mean? mine doesnt have a computer on it, so it is all done by ear.

 

Well, since you have a carb and I have EFI..it'll be a different issue. Mine is all computer controlled.

172 is "HEGO shows system always lean" and 334 is "DPFE or EVP circuit above the closed limit of 0.67 volts"

But I have no idea what that means...

Whats the HEGO system?

 

i have no clue, like i said, mine is all by ear, and the closest thing i have to a computer is the ignition box on the fender, and the cd player, is there any way that you can take the codes to a shop and see if they can decipher what they mean, and didnt you say that it is runnin rich? that wouldnt make any sence about the code sayin that it is runnin lean.

 

Well, i think what's happening is the ignition system isn't burning the fuel right, causing a poor 02 sensor reading. Maybe it's telling the computer it's running lean, and the computer is richening the mixture to compensate. I have a guy at a shop trying to look it up for me...but I put it here too to see if anyone had any addition information.

 

aight, wish i could help you better, not real good with the computer stuff, but will be happy to give you help in any arena that i can, if it had a 4bbl, i could do more.

 

i had a problem for a couple days of a poor idle on start up, it was my red secondary fuel supply vaccum tube. it was kinked, fixed it and no more bad idle. i also had an 02 code but i have no smog pump.

 

HEGO=Heated Exhaust Gas Oxygen sensor.

Were the codes you're getting key on engine off, key on engine running, or the stored codes you get after the engine off codes?

For code 334, basically it's saying the EGR valve isn't closed and it should be. This could be a bad EVP sensor giving the PCM a false reading, or a sticking EGR valve, or possibly a bad EGR vacuum regulator.

My manual lists a lot of possibilities for your other code, 172. Injectors, O2 sensor(s), AIR system, PCV valve, canister purge, MAP sensor, and ignition coil. This is just a guess, but if you think it's running rich, maybe something's making the PCM think it's lean, so it adds more fuel when it doesn't need to, creating a rich condition.

Neither of those really relate to your tach problem though (unless 172 is coil related). Maybe your tach head in the dash is going bad. Do you have another one you could try?

 

I think you are right on with this statement. A misfire will send extra oxygen into the exhaust. Have you checked timing?

 

Silly question and I don't want to insult your intelligence, but did you take out all of the components for the MAF conversion? Like the conversion module that goes inline at the engine wiring harness connector on the driver's side fender well?

Also, those stinking EVP sensors do crazy things. Any variation of current or voltage to or from the PCM will make them not read properly and pop a 334 code. Just about any electrical problem will make them do that, so I wouldn't concentrate on that 334 for right now.

Probably not any help to you, but oh well, I tried. I've learned not to take anything for granted with these things.

 

I know the tach head is fine and my fuel system is fine. The codes were stored in the computer. I took all of the MAF equipment out, the problem was present while the MAF was in as well, I put the SD back to make sure the MAF conversion kit didn't cause the problem. I was driving it for about 2 weeks before a check engine light came on, the code 172, and a few days later another one came on, the 334. The mechanic did a scan on his snap on scanner, tested w/ the engine off, and on, but I got those two codes on my own first, through the manual way of grounding the STI wire and using the blinking check engine light. I then took it to his shop to see if he could find anything else, but we both just got the 172 and 334.

I havnt checked the timing, but it seems to me like the spark plugs arn't firing enough, or at the right times or something of that nature. Basically, what would cause my ignition to fire incorrectly based on my two codes and what i've already singled out as not being a problem (like the coil and the spark plugs/wires/cap/rotor. It's kind of confusing so i'm trying to keep it as simple as possible. The problem has something to do with causing the tachometer issue, my engine problem is making it flicker. It can't be something as simple as just the timing being off, because that wouldn't explain the tach problem (but I should check it anyway to see whats going on, good suggestion). Just know that I am sure the tach head is fine, I dont want to get into the reason why I know that because it will complicate the subject.

Eric (EPNCSU2006), has given me some suggestions, like the pip/hall effect sensor, or possibly the TFI module. I brought the post here incase anyone else had anything to add, your help is greatly appriciated Eric. Did you get my reply e-mail by the way, I didn't hear back and I've been having trouble with my e-mail system.

I bet the 172 code is just a result of the problem, the 334 intrigues me (the definition I gave above is the only one for that code listed from fordfuelinjection.com).

 

I had an old BMW that wouldn't run right, would pop in the intake, the tach was all over the place and the engine sometimes would not start. Turned out it was bad bearings in the distibutor. Nothing was accurate because the shaft was all over the place.