Gas mileage has dropped

[gbarrett]

Okay, I took the big red truck for a test drive since we're taking it on a 3600 mile round trip vacation. When I was reassembling the engine last week (see post about water in the oil) my friend at the machine shop told me to block off the EGR valve and it would help. Well, I left it bolted in, but I didn't hook up the vacuum to it. And, I left other "non-essential" vacuum lines off and plugged the ports. My gas mileage has dropped and I'm not sure where to start. Does this stuff have anything to do with it or should I try putting it all back?

Thanks,

Greg

[SpruceMoose]

the carb is set up to co-exist with all the smog crap. its probably running rich now. pull the plugs and check them for black deposits (rich indication). i took all that crap off when i switched to efi, and its self-adjusting to the correct mixture, so no worries.

sm

[gbarrett]

You're right, it is running rich - black smoke out the exhaust. So, how do I fix that? Different jet(s) or needles?

Time is kinda pusing me here. Any help is GREATLY appreciated.

Thanks,

Greg

[SpruceMoose]

well, you could start by hooking up the egr valve again. d@mn, i hate to say that! but that should lean it out a bit. i dont know too much about adjusting these carbs. i've got lots of experience with twin SU types on british sports cars. actually, a very good, simple setup. despite what most people say. about the only thing i can think of to try with the carb would be to switch to a smaller set of jets. or, and this is kinda strange: lower the float level a bit to lean it out over the whole operating range, and then back out the idle mixture needles to get the proper a/f ratio for a good idle (if needed). dont know if that will work. just a thought.

or quick, go get an efi setup! ;)

sm.

[reddog]

<BLOCKQUOTE>quote:</font><HR>Originally posted by gbarrett:
Okay, I took the big red truck for a test drive since we're taking it on a 3600 mile round trip vacation. When I was reassembling the engine last week (see post about water in the oil) my friend at the machine shop told me to block off the EGR valve and it would help. Well, I left it bolted in, but I didn't hook up the vacuum to it. And, I left other "non-essential" vacuum lines off and plugged the ports. My gas mileage has dropped and I'm not sure where to start. Does this stuff have anything to do with it or should I try putting it all back?
Thanks,
Greg<HR></BLOCKQUOTE>

What is the problem that disconnecting the EGR is supposed to help?? If you have the stock emission stuff and the DSPOs have not "fixed" anything then I think you might try hooking things up. In my experiance vacuum leaks cause the most problems and are usually the lines themselves or possibly the carb mounting. JMHO

Kerry

[JOECOOL]

I have to side with Reddog. You will need the EGR or it will rattle, ping under load.
But that is not why it is too rich as a lack of a EGr will cause it to run too lean at mid throttle when the egr would be opening.
It only takes a few hours to rebuild the carb.
For such a long trip I would run it by a trusted mechanic to be sure rather that guessing.

[reddog]

<BLOCKQUOTE>quote:</font><HR>Originally posted by gbarrett:
You're right, it is running rich - black smoke out the exhaust. So, how do I fix that? Different jet(s) or needles?
Time is kinda pusing me here. Any help is GREATLY appreciated.
Thanks,
Greg<HR></BLOCKQUOTE>

If you still have the 2150 carb first thing to check is the power valve. Pull the vacuum line off the nipple on the bottom-front of the carb. That sends the vacuum signal to the power valve. If there is ANY liquid there you have a blown valve. It will cause a rich condition that shows especially at lessor throttle openings.

Kerry

[gbarrett]

Regarding the DSPO, there were many things missing when I aquired the truck. The air pump and related components were gone. That's why the machinist recommended I plug the EGR valve.

When I had reinstalled the top end of the engine, I plugged all the vacuum ports on the carb - should I have not done that? Does the power valve require a vacuum or does it supply one? I have a vac diagram, but the related smog pump paraphanalia does not exist, so I'm not sure how one would try to reconnect it.

[reddog]

<BLOCKQUOTE>quote:</font><HR>Originally posted by gbarrett:
Regarding the DSPO, there were many things missing when I aquired the truck. The air pump and related components were gone. That's why the machinist recommended I plug the EGR valve.
When I had reinstalled the top end of the engine, I plugged all the vacuum ports on the carb - should I have not done that? Does the power valve require a vacuum or does it supply one? I have a vac diagram, but the related smog pump paraphanalia does not exist, so I'm not sure how one would try to reconnect it.<HR></BLOCKQUOTE>

A couple of things need vacuum. Yes the nipple that feeds vacuum to the power valve (you are running the 2150 motocraft??) is required. Reconnecting that should help if not fix your rich condition.
The way it works is when the throttle is opened (you stomp on the gas) vacuum drops to little or none. This drop in vacuum signals the power valve to supply more fuel to the motor to increase power output.
The second thing that requires vacuum is the vacuum advance on the distributor. On the 84 you likely HAD the dual CTO setup. A CTO is Jeeps term for a vacuum switch controlled by tempeture. The system works by supplying manifold vacuum to the distributor while the engine is cold then ported vacuum after the engine warms up. If you have the heavy duty cooling option then there is another CTO that reverts distributor vacuum back to manifold vacuum if coolant temp goes above 220. You also may have/had a "non-linear vacuum regulator" valve. Its function is to supply a "mix" of both ported and manifold vacuum to the distributor depending on load. Likely more than ya wanted to know ehh?
If you don't have to worry about emissions testing AND you don't have the original CTOs intact then I would run the vacuum advance from manifold vacuum and time it by ear.

I would reconnect the EGR to manifold vacuum if you don't have the original setup. On an 84 I think you should have/had a vacuum dump valve which dumps EGR vacuum during WOT so the EGR is closed during wide open throttle.

IMHO I would try those things and see what that does. Let us know how it works out.

Kerry

[JOECOOL]

So you did plug the line in that cup under the front of the carb?
Yes thats what supplies vacuum to the PV.
That wouuld be the cause of the rich condition.
That has to run to a constant vacuum source.
AT idle (high vacuum) is keeps the PV closed letting the carb only feed from the main jets.
As you work the throttle the PV opens anytime the vacuum goes below a specified reading ( on a 2 stage power valve its usually around 12 HGs partial open then fully open at around 6.5 HGs).
Also the air pump is really not needed as all that does is blow fresh air into the exhaust to lower emmisions and shouldnt affect you motor. The other stuff I will need especially the Egr as the carb is jetted to run with it. If you remove it you need to compensate by rejetting the carb.
I always plugged my EGR because I ran a Holley that didnt need it.

[gbarrett]

I just want to make sure I understand this. I need to connect the port at the base/front of the carb to a mainfold vacuum source, right? The EGR just requires a single vacuum line from carb or manifold? I think I'm beginning to understand this, but I want to be sure.
My past experience in building engines has been either multi-port fuel injection or non-EGR based carb systems.

Thanks, you all are a GREAT help!!

Greg

[Jowersgd]

This is interesting. The cup on my power valve has been capped for some time now. I havn't noticed a rich condition though. Where exactly does the vacuum hose come from that hooks onto the power valve?

[reddog]

<BLOCKQUOTE>quote:</font><HR>Originally posted by gbarrett:
I just want to make sure I understand this. I need to connect the port at the base/front of the carb to a mainfold vacuum source, right? The EGR just requires a single vacuum line from carb or manifold? I think I'm beginning to understand this, but I want to be sure.
My past experience in building engines has been either multi-port fuel injection or non-EGR based carb systems.

Thanks, you all are a GREAT help!!

Greg<HR></BLOCKQUOTE>


Yes the power valve should connect to manifold vacuum. It is a little cup on the bottom of the carb bowl with a nipple on it. EGR can connect to manifold vac also and see how that works for you.

Kerry

[reddog]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Jowersgd:
This is interesting. The cup on my power valve has been capped for some time now. I havn't noticed a rich condition though. Where exactly does the vacuum hose come from that hooks onto the power valve?<HR></BLOCKQUOTE>

This is a 2150?? With out a vacuum source to the power valve it should be dumping fuel unless something else is wrong. Vacuum source on my 87 comes from one of the nipples on the rear of the intake manifold.

[Jowersgd]

Yep this is a 2150. I paid someone to put it on back before I knew anything about my GW mechanically. The nipple is capped on the power valve cup. I would really like to hook it back up but I don't know where to connect it. My EGR is also unhooked, I don't know where that goes either. When you say manifold and ported vac, I'm not sure what you're talking about. After reading this thread I'm a little worried about my set up.

[Jowersgd]

Just now I went outside and had a look at the vacuum catatsrophy I apparantly have under the hood of my truck. I looked around and saw two nipples on the manifold that had been plugged. I guess those are manifold vac. Both were sorta behind the carburetor. I unplugged one and ran a hose from the EGR to it. The car ran like poop. So I unplugged the egr and connected the power valve to the same nipple and again the car ran like poop. So, did I hook things up wrong? or is the carb set lean to compensate for having the power valve plugged. Also, consider this: the older model 2150-2 (the one with the mechanical bowl vent) didn't have a nipple on the power valve bowl. So if having mine plugged would cause it to run rich, did the older models run rich too? Here's another thought: I think I read somewhere that the older trucks without EGR's had carbs that were jetted richer. Since my egr is not hooked up, could my power valve bowl be plugged to compensate for not having the egr hooked up. I know all this is confusing, believe me I am. Any advice/suggestions would be appreciated.

[ July 13, 2001: Message edited by: Jowersgd ]

[JOECOOL]

Jowersgd,
On the older carbs the vacuum source was internal. A passage drilled from the inside of the PV cup to the base inside the carb. So there should be no external nipple on those cups unless the cup was transplanted from a newer carb.
Yes the non EGR carbs were jetted richer.

[reddog]

[QUOTE]Originally posted by Jowersgd:
I looked around and saw two nipples on the manifold that had been plugged. I guess those are manifold vac. Both were sorta behind the carburetor.

Correct - those are manifold vacuum.

I unplugged one and ran a hose from the EGR to it. The car ran like poop.

You might try hooking the EGR up to ported vacuum. Ported vacuum comes from the carb so there is little if any vacuum until RPMs come up. Hooking the EGR up to ported vacuum will cause the EGR to stay closed at idle. Your EGR diaphram may also be ruptured so it may be causing any vacuum source hooked up to it to just become one big leak.

So I unplugged the egr and connected the power valve to the same nipple and again the car ran like poop. So, did I hook things up wrong? or is the carb set lean to compensate for having the power valve plugged. Also, consider this: the older model 2150-2 (the one with the mechanical bowl vent) didn't have a nipple on the power valve bowl. So if having mine plugged would cause it to run rich, did the older models run rich too? Here's another thought: I think I read somewhere that the older trucks without EGR's had carbs that were jetted richer. Since my egr is not hooked up, could my power valve bowl be plugged to compensate for not having the egr hooked up.

Rudy is the carb expert so I'll yield to him after I give my $.02 worth. I don't think you could balance the lack of an EGR by causing the power valve to always be open. WAY too much fuel. Likewise you could not easily balance having the power valve always "on" by rejetting the carb and/or adjusting float level. It would be much easier to just fix the problem correctly.

How much emiisions stuff do you have installed?? Is everything left stock??

Kerry

[Millerluck]

I 2nd Reddog.

The EGR needs ported vacuume.
If you send manifold vac. at idle it will cause it to stall.

Just my .02

Later

Larry Miller