Interesting vacuum gauge results?

I have been trying to locate the cause of a engine skip or transmission problem for some time on a 2003 Windstar. There are no codes and it only does it under a light load(for example going up a long hill on the interstate) Here is what I found out today. I hooked up a vacuum gauge today and the engine is text book for a properly running engine at idle and blipping the throttle. So I hooked up a long hose and went for a long drive watching the gauge. What I started to notice was when it is in overdrive and slowly speed up or I give it more gas to go up a hill(with "out" dropping out of overdrive very important) the vacuum drops as it should. However when the vacuum gauge hits the 2 pounds mark every time the van starts to buck/skip/studder, etc. When I make it down shift prior to the 2 pound of vacuum mark it did not buck/skip/studder, etc. I was able to duplicate this over and over. So the question is what does this mean? I am thinking the kick down cable is not adjusted properly(streched?) is the vacuum supposed to drop down to 2 pounds before it down shifts or there is something else that is not functioning properly. This is what I need help understanding. What should I look at next?

Thanks for your help.

I would like for you to take the very same test, but with the EGR disabled. Just pull and plug the control vacuum line that goes atop the EGR valve. This may give you a code/engine light ... but, who cares.

Hi,

I have already done the test you described, but with out the vacuum gauge attached. I will repeat the test tonight with the gauge. I am courious to see what happens. However when I tried this before it did not make a change and it still had the same problem as described in my origional post. If it does continue to buck/skip/studder etc. at the 2lb vacuum mark with the EGR unpluged what else could this point to?

Thanks for your help.

I am now a bit puzzled. Was hoping it was EGR related.

I'm assuming, because the vacuum increases as the throttle is opened, that your vacuum sample-port is on the high pressure side of the throttle plate. ....??

I have two hunches .... (1) the cam synchronizer is not in exact postion, therefore the injectors are not firing when intake air velocity is at its maximum. ... or (2), you have some valve and seat issues .... have you made a compression test?

okay, I was able to run the vacuum gauge test with the EGR unpluged and the line pluged. No Change. Now that I have been driving my wifes van more tring to fix this I have to add another symptom. Taking off from a dead stop(jack rabbat type) when the vacuum gague 0's out it acts like I left the choke on to long in my old MG. It does this for a few secounds and then recovers when I let off the gas. I do not know how long it will do this I did not want to take the risk of hurting something, but I did hold it in this condition for what seemed to be a few seconds.
I am also confused about your suggestion about "(2), you have some valve and seat issues .... have you made a compression test?" I am still learning the art of reading a vacuum gauage, but everything I have read about how the needle moves at idle and blipping the throttle points to a sound engine. It does not flutter/jump or move sluglishly at all.

How do I test for "(1) the cam synchronizer is not in exact postion, therefore the injectors are not firing when intake air velocity is at its maximum."

Perhaps any other ideas.

Thanks for your help.

The cam sensor is positioned properly ... by having the crank at TDC (compression stroke) ....and aligning the cam pos synchronizer, using a small plastic tool made for the task. A unique tool is needed for each engine by year model.

I still must ask: Where, relative to the throttle plate, are you sampling vacuum?

Burned valves and seats can caused engine stumbling, especially under load.

I am hooking the vacuum gauge to the air intake plenum port for the fuel pressure regulator. Is there a better place to take this readings from?

I have been taking my vacuum readings by disconnecting the hose to the power brake booster as it doesn't change anything within the engine. I do not recommend using that port if you are going to take it for a test drive, however, as your brakes won't work so well without vacuum to the booster. And please correct me if I am fudging my readings by using that port.

Many cars have a vacuum manifold, mounted to the firewall, that feeds vacuum to many things ... including the vacuum brake booster. Usually there is an unused port on this manifold that is capped off with a rubber cap. Using this extra port leaves everything else hooked up ... giving you the best readings.

Or: .. http://www.secondchancegarage.com/public/186.cfm

Any resolution on this problem? I'm having an extremely similar problem.

Mark

Update, So far so good. It looks like I have a Windstar with exspensive taste and only likes Motorcraft parts. The Aftermarket wires and plugs seem to have been the problem(went through two sets of each). I replaced them today and went for a drive and hit all the loctations(hills) were the skip happens with out fail. So far so good. I have my van back. I may give up the idea of trading it now.

Now on to the AC that just died. Any body know the Motorcraft compressor part# for front and rear zone AC system. On Rock Auto I believe there is two or three diffrent Motorcraft part#'s listed. Or a good recomendation.

Update, So far so good. It looks like I have a Windstar with exspensive taste and only likes Motorcraft parts. The Aftermarket wires and plugs seem to have been the problem(went through two sets of each). I replaced them today and went for a drive and hit all the loctations(hills) were the skip happens with out fail. So far so good. I have my van back. I may give up the idea of trading it now.

Now on to the AC that just died. Any body know the Motorcraft compressor part# for front and rear zone AC system. On Rock Auto I believe there is two or three diffrent Motorcraft part#'s listed. Or a good recomendation.

Ford/Motorcraft site:

http://www.fordparts.com/Landing/Motorcraft.aspx

link for compressor #:

http://www.fordparts.com/Commerce/CatalogResults.aspx?y=2003&m=Ford&mo=Windstar#Search

you could also try www.tascaparts.com (http://www.tascaparts.com)

hope this helps