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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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Old 02-13-2011, 09:45 AM
slavinpavin slavinpavin is offline
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1996 F350 5.8 Bad EGR or Bad Valves. Both?

Hello Folks,

Having issues with this truck and could use some advice please. The truck has a backfire through the exhaust and hesitation after I decel then slight accel.

After searching the forums, I found that it may be the EGR. So I unplugged the vacuum hose and it stopped the backfire but the mileage is still awful at about 7.5 mile per gallon. I am wondering why it started backfiring in the first place. I am leaning towards a bad valve or two.

The valve seals are starting to go since it is starting to puff blue smoke. I also hear pinging when accelerating hard. Could just be the way it is as it did that with the EGR vacuum line on also. The truck has 180000+ miles but the engine was reman by Ford at some point (done before I bought it). The oil changes have been kept since I have had it, so I don't want to think it is the valves or lifters but not sure what else it could be. The truck starts fine and it goes good at WOT.

I have done a complete tune up and spark plug wires are right and separated (7&8). Vacuum lines are intact and sea foamed it through the booster line, and no difference. There was no CEL on when the EGR line was on, but now there is after unplugging the vacuum line (normal).

Would simply unplugging the EGR vacuum line keep the mileage poor? Any thoughts? Thanks!
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Old 02-13-2011, 10:09 AM
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The pinging on hard accel brings a thought of carbon in the cylinder's or else the timing is too far advanced.

I have heard many Posters here say that stopping the effect of the EGR will produce even hotter combustion temps. If it isn't working, you should dissassemble and find out why. You stated that you already Sea-Foamed the intake, yet I'm unsure if you have noticed the pinging since then. If you are still getting Pinging at WOT, check timing, then I would have to remark, it's either time to switch to 89, 91, or 93 octane and see if the pinging quits. If your more apt to the idea of removing the head's, then I would do so, have the heads cleaned, valves replaced, new valve guide seals, clean the top of the Pistons free of carbon.
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Old 02-13-2011, 10:50 AM
slavinpavin slavinpavin is offline
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Thanks for the quick reply! The pinging is still there after the Sea-Foam. I would assume the sea-foam would've removed the carbon build up if there was some. I'll check the timing as that sure would do it too. I'll also disassemble the EGR to check that too. Don't want to spend the money on higher octane gas but will try a tank to see if the pinging stops.

So, if the EGR valve is operating freely and the timing is right on, what else could cause the backfire and slight hesitation?
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Old 02-13-2011, 11:41 AM
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I did forget about the valves from my earlier reply. Yes, the 2 valves located in the rear of the Engine(that is where mine are located on my 5.0) could be allowing air back thru, and hence the back-fire. I did end up replacing the one valve that controled air into the head, since it leaked air opposite of flow of direction and was nasty inside period. The lower one is the tube running from the exhaust.

If you have the time and effort to get back behind the engine and remove them(top one is easier than the lower one) you can check for air oppposite the direction by blowing thru them. I haven't had the same experience with backfire in either my 4.9 or my 5.0, so I trying to remember from other members who experienced the same problem with backfire. I don't want to get flamed for this but I believe the lower valve controlling air from the exhaust so that it doesn't come back up thru the head sounds like part of your problem.

2 other things I didn't suggest when I 1st replied to your post.
1st, Definately try the search function, and use quotes around your search term.
2nd, Have you pulled or checked for codes?

These 2 statements will help further your diagnosis and others who may ask if you have already. In certain cases, there may not be a CEL light but ther could be stored codes, or may come to find out it hasn't thrown a code yet, since the situation hasn't gotten to far out of hand.
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1992 F-150 V8 302 156K 4x4, SuperCab, Auto
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Old 02-13-2011, 12:39 PM
slavinpavin slavinpavin is offline
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Now I'm confused. There are valves that control the flow of air (possibly near the rear of the engine)? I haven't look closely at the EGR setup yet, but are these valves connected to the EGR or something else? Obviously there is a tube to capture the exhaust gas but there is another? I gotta take a closer look.

I'm not sure how to check for codes on a OBDI setup but there was no check engine light on before I pulled the vacuum line from the EGR only after, which makes sense.

Thanks for the search suggestions and your help.
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Old 02-13-2011, 01:25 PM
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The 2 check valves i am speaking of are located behind the rear of the engine. 1 is connected to the "WishBone" tube behind the engine, bolted to each head. The 2nd, runs down to the exhaust.

1st thougth is to check the smog pump for proper operation. If it isn't supplying air to the Thermactor system, the deceleration would allow un-managed exhaust gases back thru, hence it may backfire.

Try this link to check for Codes.
Ford Fuel Injection » How To Run a Self-Test
Also, you can can flip thru all of this site for more information that you can'tnormally find anywhere else.
Ford Fuel Injection
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1992 F-150 I6 4.9L 300 110K 4x4, SuperCab, Manual
1992 F-150 V8 302 156K 4x4, SuperCab, Auto
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"These ideas, evaluations, opinions are representations of real-life scenarios and backed by Murphy's Law..."
"Inferior parts lead to immediate failure sooner than later..."
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Old 02-13-2011, 04:27 PM
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Thank you for the links. When I can get into it, I'll report back so maybe it will help someone else out. Should be within the next couple days.
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Old 02-14-2011, 03:38 PM
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I got to take a quick close look today and can see the tubes that you were talking about. Boy those things are back there! Gonna have to wait until the weekend to dive into it. The truck is used daily for my trash biz, so I can't take the risk of not being able to finish what I started.
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Old 02-19-2011, 06:48 PM
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Well, I got the upper intake off and can now see a little better. There are 2 check valves on the thermactor tubes. I want to replace them but they seem to be part of the tubes(not able to remove). Maybe they can come off from the tubes somehow. Anybody know how?

Also the tube that connects the egr to the exhaust manifold is wierd. There is a part of the tube that looks like a flex pipe but it's not and it just kind of sits there. At this point I am ready to torch the truck! Everything is such a pain. Like the 1 torx screw on the intake. WHY?!

I have to fix this truck by Monday and working outside in 30 degree temps is not fun. I really want to pull the lower intake off but I don't have the time for all that.

So if anyone knows how to take the check valves off, please let me know.
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Old 03-05-2011, 02:30 PM
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UPDATE: Replaced EGR valve, evp sensor, and all vacuum lines. Truck doesn't backfire anymore and is getting a little better mileage but seems to not have too much top end power. Gotta stay in it on the highway to keep at 65 and need to downshift when going up small hills.

Pulled codes and have 334 and 212. Looked through the forums and more. Bought a multi meter but not really sure how to check the evp sensor. I tried putting the old evp back on resetting the codes and still get the same ones.

I am guessing there is a short somewhere but not sure which wires exactly to probe for continuity. Also the 212 code throws me for a loop.

The truck now continuously smokes at idle after being warmed up (I think it looks bluish and my wife thinks it looks more grey) . Doesn't smoke at all when first starting on cold engine. Any suggestions?
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Old 03-05-2011, 02:48 PM
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bluish smoke indicates coolant being burnt... have you seen any water in the oil? May be a head gasket. or if you have an oil cooler like my F250 has, that is a common place for water to get into the oil. Food for thought
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Old 03-05-2011, 02:53 PM
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No water in the oil and the coolant level hasn't changed. I always thought that blueish smoke is oil burning. IDK, about spent working on this truck!
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Old 03-19-2011, 05:23 PM
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UPDATE: Broke down and brought it to the shop. They said it is definitely seals. They did a compression test and a leak down test. Compression was within range but the leak-down had a 10% loss. So seals it is. When I replace them I'll report back so others may be able to learn from this.
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Old 03-19-2011, 05:52 PM
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Sorry I missed hearing about your updates...The blueish smoke was a good indication the valve guide seals were bad. I had the same problem but also my head gaskets were shot and not sealing. I just had both heads removed, cleaned, valve job and new valve guide seals..No more smoke...

Look forward to hearing the final result when you get it back.
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1992 F-150 I6 4.9L 300 110K 4x4, SuperCab, Manual
1992 F-150 V8 302 156K 4x4, SuperCab, Auto
"He's one brick shy of a load..."
"These ideas, evaluations, opinions are representations of real-life scenarios and backed by Murphy's Law..."
"Inferior parts lead to immediate failure sooner than later..."
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Old 03-19-2011, 08:43 PM
slavinpavin slavinpavin is offline
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I'd love to take the heads off and have them redone but I just don't have the down time for this truck. I don't know of any machine shop that could do it in 1/2 day on a Sunday! And I sure as heck can't myself.

I'm really considering buying new heads. Advace has got them for about $250 a piece. But if I do that then that means new lifters, pushrods, the works. Wound up being like $800 for everything. Not to bad but I can get a long block for $1600. So I guess I'll just do the seals and hope to get another year or so out of this old girl.

Timber.. after looking closer I found out that my AIR tubes go into my exhaust manifold instead of the heads. Not sure why/what the difference is but thought you might like to know. Thanks for your help man.
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Old 03-19-2011, 08:43 PM
 
 
 
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