Bad exhaust donut and O2 sensor

jremington59 · 11-02-2009, 08:52 AM

I have a 94 with a 5.7 in it. Recently the exhaust donut blew out and shortly thereafter the engine started running badly down low.

I did a little reading and found that an exhaust leak prior to the O2 sensor can throw off the readings it gets. It also seems to have affected my gas mileage.

Can this really cause this much trouble with the engine?

bradrhale · 11-02-2009, 11:31 AM

yes it can cause a problem especially if the wires have gotten around it from the O2 sensors. the donut is not that difficult to replace although, you might have to buy new bolts to replace the ones that are just waiting to twist apart. after that, erase the codes and see if the truck runs better. are you getting an SES light??

jremington59 · 11-02-2009, 07:26 PM

Ocassionaly the check engine light comes on, but will go back off after I accelerate.

I need to get it changed but I know I'm going to have problems as the nuts are completely rusted. I've used the truck for plowing the last couple years and the rust is really beginning to set in. I figure if they break then you have to pull the exhaust manifold and drill it out?

I have let things go all summer and now I'm trying to get all the vehicle repairs done before the snow falls. Today I got the sway bar links changed.

Thx for the insight....

bradrhale · 11-02-2009, 07:34 PM

WHOA, WHOA, WHOA!!!! i thought the donut was bad at the collector?? not the exhaust manifold??
its a 94 model. look up pulling OBD1 codes with a paperclip before doing anything to your truck. you will get at least one 2 digit code. get that as it might shed some light as to exactly what is happening in your engine.

BernieB · 11-02-2009, 08:26 PM

With any exhaust work it's not if the bolt breaks. It's WHEN the bolt breaks.

I never even start any exhaust work until I already have replacement bolts or studs on-hand, and a couple of sharp titanium coated cobalt bits for drilling things out.

jremington59 · 11-02-2009, 08:51 PM

I've never drilled out the manifold before. Do you drill right through and use around a 3 inch length, 1/4 inch bolt? And can I make the exhaust manifold gasket or should I buy a new one? Or isn't it necessary to remove the manifold?

I'm also confused what you mean by "pulling OBD1 codes with a paperclip".

BernieB · 11-02-2009, 09:51 PM

Quote:

Originally Posted by jremington59

I've never drilled out the manifold before. Do you drill right through and use around a 3 inch length, 1/4 inch bolt? And can I make the exhaust manifold gasket or should I buy a new one? Or isn't it necessary to remove the manifold?

It depends on the bolt naturally. And no, you shouldn't need to remove the manifold.

For what you're doing there even used to be clamps that could be fit to the two flanges and then tightened down, eliminating the need to drill out the old bolt.

If it's the type that uses an actual bolt and nut (with or without the springs) you can sometimes pop the broken bolt out with a drift punch, but drilling straight through works also. If it's a stud, and not a bolt, you may not be able to drill all the way through, and have to use a clamp. My advice to you, before you even start the job, is to visit your local parts place and see what they carry to fix a broken stud or bolt in that situation.

There's been a few over the years when I've had to drill and tap the hole for a new stud.

BernieB · 11-02-2009, 09:52 PM

Quote:

Originally Posted by jremington59

I'm also confused what you mean by "pulling OBD1 codes with a paperclip".

There should be info on this in the General Truck forum. Look at the threads that are "stickied" and you should find it.

crabtruck · 11-04-2009, 12:08 AM

When I checked the General Truck Reference thread it suggested
that I would also like the bowling and diet threads.

Here's a link for pulling codes with a paper clip Just Wondering
This works for "OBD-I" which is trucks 1994 and older.
OBD-II is 95 and up, and they require an actual code reader.
OBD stands for On Board Diagnostics - tests that the truck's computer runs.
Codes are just it's way of noting anything strange it sees.
SES light may be on or off while codes are "in memory" (still available)

On your truck the connector you are looking for is stuck to the bottom edge
of the dash on the left near parking brake handle.
If you were standing 4' away from open door you should see it.
There are many threads here dealing with this.
Search for OBD or paperclip or ALDL or DLC.
ALDL and DLC are names for that connection where paperclip or reader goes.

jremington59 · 11-04-2009, 07:39 AM

Thx for the info.

11-02-2009, 08:52 AM	#1
jremington59 Full Member Join Date: Oct 2009 Posts: 29	Bad exhaust donut and O2 sensor I have a 94 with a 5.7 in it. Recently the exhaust donut blew out and shortly thereafter the engine started running badly down low. I did a little reading and found that an exhaust leak prior to the O2 sensor can throw off the readings it gets. It also seems to have affected my gas mileage. Can this really cause this much trouble with the engine?

11-02-2009, 08:26 PM	#5
BernieB Senior Member Join Date: Jul 2009 Location: Fredericksburg, VA Posts: 1,910	With any exhaust work it's not if the bolt breaks. It's WHEN the bolt breaks. I never even start any exhaust work until I already have replacement bolts or studs on-hand, and a couple of sharp titanium coated cobalt bits for drilling things out. __________________ If the guys who design 'em had to take one home, use it every day for 2 years, and do all the maint and repairs themselves, cars would have a button on the dash to change the oil, filters & plugs.

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11-02-2009, 11:31 AM	#2
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 8,030	yes it can cause a problem especially if the wires have gotten around it from the O2 sensors. the donut is not that difficult to replace although, you might have to buy new bolts to replace the ones that are just waiting to twist apart. after that, erase the codes and see if the truck runs better. are you getting an SES light??

11-02-2009, 07:26 PM	#3
jremington59 Full Member Join Date: Oct 2009 Posts: 29	Ocassionaly the check engine light comes on, but will go back off after I accelerate. I need to get it changed but I know I'm going to have problems as the nuts are completely rusted. I've used the truck for plowing the last couple years and the rust is really beginning to set in. I figure if they break then you have to pull the exhaust manifold and drill it out? I have let things go all summer and now I'm trying to get all the vehicle repairs done before the snow falls. Today I got the sway bar links changed. Thx for the insight....

11-02-2009, 07:34 PM	#4
bradrhale Senior Moderator Join Date: Apr 2006 Location: Texas Posts: 8,030	WHOA, WHOA, WHOA!!!! i thought the donut was bad at the collector?? not the exhaust manifold?? its a 94 model. look up pulling OBD1 codes with a paperclip before doing anything to your truck. you will get at least one 2 digit code. get that as it might shed some light as to exactly what is happening in your engine.

11-02-2009, 08:51 PM	#6
jremington59 Full Member Join Date: Oct 2009 Posts: 29	I've never drilled out the manifold before. Do you drill right through and use around a 3 inch length, 1/4 inch bolt? And can I make the exhaust manifold gasket or should I buy a new one? Or isn't it necessary to remove the manifold? I'm also confused what you mean by "pulling OBD1 codes with a paperclip".

11-04-2009, 12:08 AM	#9
crabtruck Senior Member Join Date: Jul 2007 Location: on your 9 Posts: 3,366	When I checked the General Truck Reference thread it suggested that I would also like the bowling and diet threads. Here's a link for pulling codes with a paper clip Just Wondering This works for "OBD-I" which is trucks 1994 and older. OBD-II is 95 and up, and they require an actual code reader. OBD stands for On Board Diagnostics - tests that the truck's computer runs. Codes are just it's way of noting anything strange it sees. SES light may be on or off while codes are "in memory" (still available) On your truck the connector you are looking for is stuck to the bottom edge of the dash on the left near parking brake handle. If you were standing 4' away from open door you should see it. There are many threads here dealing with this. Search for OBD or paperclip or ALDL or DLC. ALDL and DLC are names for that connection where paperclip or reader goes.

11-04-2009, 07:39 AM	#10
jremington59 Full Member Join Date: Oct 2009 Posts: 29	Thx for the info.