Vacuum Leak help...

[Expy_97]

Ok, so I have been chasing this leak for a while now. I have replaced all of the rubber hoses (not the plastic ones), including the Fuel Tank vapor lines to the canister and back to the Purge valve. I have replaced the entire EGR system - EGR valve, EVR, DPFE and hoses, as well as the drivers exhaust manifold and EGR tube. Also replaced the hidden elbow under the IAC valve and the IAC valve itself. I STILL HAVE A VACUUM LEAK.

Symptoms -
At Idle in Park or Drive - Vac = approx 20-22 inHg
At 3000 rpm in Park - Vac = Approx 22-25 inHg (this throws out the Catalytic Converter clog possibility?)
At 3000 rpm in Drive - Vac = 0 inHg
Vac leak gets worse with more throttle - if I only give it about 10% throttle travel, the vacuum holds in 15-18 range, but it I give it even a tiny bit more than that it will drop relative to how much throttle I give it. If I give it 25% throttle, it will drop to 0. If I hold it at 0 for 10-15 seconds it will start missing and throwing codes P0308, P0800, P0020 which I assume is due to flooding out because the vac is so low and the FPR is dumping fuel into the cylinders. Other than holding it at 0, I get no codes. I have reset the PCM and it will no longer clear the catalyst monitor, but it does not throw any codes unless I create the low vacuum situation.

Since I have replaced everything that I can find on this thing, I would entertain the possibility that I have installed something incorrectly. Give me anything you can think of that fits the symptoms. I am not 100% sure that I got the EGR tube mounted correctly to the exhaust manifold. I have already replaced that twice now. When I installed it the first time, I did not get the tube seated correctly and it nicked up the Manifold connector. I did not replace the manifold connector as i thought I should have. It would not surprise me if that was the current problem still.

One more thing - I have clamped off the vacuum to the Fuel vapor lines to isolate that system and the vacuum leak did not go away so you can ignore that system entirely.

Thanks!!!

 

[Expy_97]

Update - EGR system

I decided to isolate the EGR tube from the main vacuum system by making the EGR valve inoperative. I removed the Vacuum hose from the top of the EGR valve.

After driving the truck with the EGR vacuum hose removed and plugged, I did notice a slightly better response from Vacuum gauge while driving and noticeable (albeit small) improvement in performance.

If the EGR tube was leaking at the exhaust manifold junction, would that still have a large effect on Intake manifold vacuum even though I removed the direct access through the EGR valve? If that is the problem, then why would I be able to generate a good vacuum while the tranny is in park, but not in drive?

 

[Expy_97]

Any Ford Experts out there...

Can anyone tell me which vacuum system would be engaged with the tranny in drive that would not be engaged with the tranny in Park? Is the difference I am seeing in vacuum related only to engine load and not to the tranny selection?

 

[toms89]

Confused?!

As you give it throttle you will lose vacuum!! Also the higher the load the less the vacuum. It does not have to be wide open throttle to lose all measurable vacuum.. Vacuum measurment is in no way linear to pedal travel.. most of vacuum is lost early in the throttle travel. Just because you loose measurable vacuum does not indicate lack of airflow!! Its actually the opposite. What your describing sounds completely normal other than the miss and throwing of the codes.

Mine starts getting into boost with 1/4 throttle maybe less. I have to be real conservative on the go pedal to maintain vacuum. (gas milage)

With the egr active it is dumping small amount of exhaust gasses back into the intake manifold so yes you will loose some vacuum. This lowers combustion temps and allows for increase in timing. This is primarily done for emissions purposes.

I dont think the problem is vacuum related at all. Its more than likely load related..

 

[toms89]

3008 is a cylinder #8 misfire according to 2000 expy service manual. The other two dont exist on my 2000 expy service manual cd rom.

Did search online and did not find any consistant answers for the two remaining codes.

 

[superexpy]

Yep, Sounds like a missfire..... I have found vacuum leaks befor by unplugging the 3/8 inch vacuum line on the left side of the throttle body and blow in it. if air excapes then you know you have a leak.