1991 Wagoneer - Basic Carb Tuning/Running Rich?

[babywag]

yes, egr should only be active when engine is fully warmed up.
get a cto, or leave it disconnected.

[rang-a-stang]

I just bought a brand new CTO from my local McParts store. It was pretty easy for them to find. I ordered this one:

https://www.autozone.com/engine-management/ported-vacuum-switch/duralast-ported-vacuum-switch-e907/3041_20571_15042&searchText=E907

Right after I installed my new one, I found my original working one in my parts stash. You can have it for shipping if you want. It is pretty small so I think getting it to the UK would not cost that much if you cannot find one there locally for cheap. My truck is a 79 so my vacuum routing may be a little different.

When I was running a carb and EGR, I had a big flat spot off idle, after warming up/CTO opening, too. Again, I am a 79 so I am probably slightly different than yours. There was a part I had to get that had about 3 different names but I called it a vacuum dump valve. On my vacuum diagram it was called the VSD Valve. It mounts between the EGR and intake manifold and senses exhaust pressure and modulates the EGR vacuum signal to do away with that flat spot. I believe a vacuum delay would do away with your flat spot but the dump valve seemed to be a better solution. The down side to the dump valve: they are IMPOSSSSSSSSIBLE to find. It took me a good 2 years to find a working one. I am willing sell mine to you but I think you would be better off trying a vacuum delay valve first.

[Brynjminjones]

Thanks both for the help!

Rang-a-stang, that's really kind, thank you!

I actually think I've found a CTO that will work. The dual CTO on the heater hose has two ports that hold vacuum perfectly. In the morning I'm going to warm it up and see if it switches properly.

I've been browsing vacuum diagrams and it seems some years use the front CTO for EGR but others use this rear one, so if it works hopefully it should do what I need.

If not though, I'll definitely be interested in that one you've got, thank you

[Brynjminjones]

I've tested my CTO this morning and it works great! Doesn't allow any vacuum through when cold, allows full vacuum with engine warm, and doesn't leak at all.

I've now hooked my charcoal canister up to this as previously it went straight to ported vacuum.
Once I've got a delay valve for the EGR I'll get that hooked up too.

I'm also considering having the delay valve in front of the charcoal canister too, as it might help richen up the initial throttle tip in momentarily, but I'll see how I get on with just EGR first.

[Brynjminjones]

I've got a little more update on this:

I've temporarily hooked up the EGR without a delay valve, as they seem almost impossible to find.
Both the EGR and the charcoal canister are now hooked up to the dual-CTO so they don't come in until the engine is warmed up a little.

I drove it about 30 miles like this yesterday to test.

As expected the throttle response is now very poor, so overall drivability is definitely worse.
I expect a delay valve will go a long way towards fixing this, but it still generally feels a lot less powerful when going up hill at part throttle.

Is that normal with EGR, or a sign that something else is off?

[rang-a-stang]

no, that is not normal, something is off. You should not even really notice EGR is working when it is working. Hopefully that is the delay valve.

[DarkMonohue]

Under part throttle and moderate load, the engine will require a slightly greater throttle opening with EGR than at the same power level without EGR, but it should be a minor difference. Not sure you'd notice it by SOTP.

[Brynjminjones]

Thanks both, it's definitely changed how it feels to drive. My girlfriend was with me and after 5 minutes of driving asked "what's wrong with her today?"!!

I actually found a delay valve in my drawer of junk yesterday. It only delays by a second or so but I'll try it out until I can get one with more of a delay.

[Brynjminjones]

Well I placed an order the other day for a NOS random vacuum delay valve from eBay. It was the only one I could find of any kind in the country.
It said it was for a '70s Ford Fiesta and didn't have a proper picture.

It arrived today and although the packaging says "Made to European Ford specification", it's actually a made in USA part almost exactly like what the Wagoneer would have come with!


I applied a vacuum to it and found it takes about 20 seconds to go from 0 to full vacuum. A bit more delay than I need but I don't see that being a problem.

I've fitted it to the Wagoneer and driven around town, and it's driving great! Admittedly, with a 20 second delay, there probably aren't too many times EGR will come in around town, but I'm hoping this will allow it to work properly whilst cruising.

I've still got another very slight hesitation (wouldn't be noticeable to a passenger) sometimes that I think is linked to the charcoal canister. I've now added my 1 second delay valve to that to see if that sharpens up my throttle response a touch.


I'm starting to see light at the end of the tunnel with all this tweaking!

[Brynjminjones]

Just posting a follow up, as I'm so pleased with how this thing is running now.

I've not really touched the carb for the last several months, and it seems like it's dialed in really nicely.
I had to move the accelerator pump up one hole to get rid of a slight hesitation when warm, but other than that it runs beautifully.

Earlier this week we drove it 6.5 hours non stop, towing a small boat behind. It didn't skip a beat the whole way, and had plenty of power.

The thing that surprised me was that it got over 14mpg! I think that's two better than quoted by the EPA when new, and this was with a boat in tow, surf board on the roof, and AC on!

Waggy and Boat by Brynjaminjones, on Flickr

[rang-a-stang]

That is wonderful! thanks for posting and what a great picture!!!

[stonybrookpictures]

Check out this article on Ported Vs Manifold Vacuum Advance.

http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm

[nograin]

Unfortunately that widely reprinted article was not actually written by a GM engineer who worked on anything related to tuning or emissions.

Evidence of this is most easily seen in this assertion:
After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements,.... and all manner of crude band-aid systems were developed .... One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle.

You can easily check this yourself by looking at a variety of vehicles made before the emissions control era.

It is true that some vehicles used manifold vacuum to control vacuum advance. I happen to have 1963 FSJ service manual and that's what was used on the engines for those jeeps.

However looking at the distributor vacuum source on Chrysler's engines in the 1960s, all used ported vacuum.
In fact in Chrysler's 1959 Master Technician's Serice Conference, its stated quite clearly


from https://www.web.imperialclub.info/Re...136/Page01.htm

Now what about GM?
Well I'm familiar with a few of GM's carburetors used on factroy high performance engines, such as the Holley List 3310 used on the '65 396 and some others. The vacuum port for the distributier is above the idle position
as it is on the 1965 Cheverolet L-78 with list 3124 (also a Holley model 4150) Here's a nice photo from the web showing the distributor line connected to the ported vacuum.



and a diagram showing the same connections on 365 hp 350



The truth is, the decision to use or not use manifold vacuum to increase advance at idle related to what the distributor could do and what the engine needed.

Pre-emissions engines ran relatively rich idle mixtures. They did so because by doing so they make more power and can be idled slower. When I write more power, I'm describing power at idle. If you've driven an old truck where you can slip it into first gear without touching the throttle, and its only idling at 500 rpms, that's what i'm talking about.

Again, no reason to beleive me over that anonymous article. Look at the actual liturature of the time.

Here again from Chrysler's Master Tech Service Conference discussion the needs of the new (60's era) lightweight high compression engines and the impact of the Clean Air Package (CAP) for California only in '67.

From page 3 of http://www.imperialclub.com/Repair/L.../240/index.htm


Whether one of our FSJ engine will benefit from using vacuum advance at idle depends on a number of factors. One of which is the distributor's mechanical advance. Another is how much vacuum the engine is producing at idle.

Anyway my point here is that its not black and white, and a caution not to believe using ported vacuum had anything to do with emissions controls.

[stonybrookpictures]

Nice job

That was good.

[Brynjminjones]

Thanks Nograin, that was really interesting.

I'd seen that article floating around probably 50 or so times now, but I never felt like I could quite trust that it was true. It's often quoted as gospel but I didn't know where it actually came from.

I did try manifold vacuum on my Wagoneer for a week, but I couldn't get it to work right at all.
It would often enter funny feedback loops where the vacuum would drop, which would reduce the timing advance, which would lower the idle, which would drop the vacuum, and so on...

I wasn't happy with it at all so put it back to ported and haven't looked back.
My Ford F100 is on manifold though and seems perfectly happy, although I don't know if I'll keep it there permanently.