Can't find my answer in the manual so... Engine stumbling on acceleration. Thought it might be EGR valve. Pushed on diaphram in idle, speed drops so that's normal. Moves freely. Checked transducer.
Exhaust gas pressure at lower port OK. Vacuum at carb port strong.
No vacuum at EGR port at idle. Weak vacuum at slight acceleration. Vacuum drops away at hard acceleration. Took transducer out to bench. Applied light compressed air to lower port and there's an audible movement. No vacuum at EGR side without pressure at lower port. Reapplied pressure at lower port and air moves through, but not what I would call freely.

Here's the Question: Is the EGR circuit designed to operate in a limited range or should the recirculated gas going into the throttle body ramp up with acceleration and drop off when you slow down? The way it's running now seems to shut off the recirc at idle, allow for a small amount at light acceleration and shut off again with heavy acceleration. If I bypass the transducer and hook the EGR direct to the vacuum line, it roars up and down with nary a stumble but the heat going into the TB doesn't seem normal (plus I don't think they would have put in the transducer if they didn't need it). The cut-away illustration in the book shows two positions for the transducer "at idle" and "under acceleration". I don't get the fact that vacuum passes through the transducer at light acceleration then disappears at heavy acceleration. It looks like a two position device, either open or closed. Am I missing something?

I'd love to help ... really, but ... it already sounds like you know WAY more about the EGR than I do!

BTT so more knowledgeable folks can respond ... <img src="/forums/images/graemlins/frown.gif" alt="" />

PS - It would probably help if we knew what year, model, engine size / type and tranny you had - that way you get the best info first with the least amount of head-scratching - kinda like this response <img src="/forums/images/graemlins/pfft.gif" alt="" /> . Most people add this info to their sig line ... see mine below.

Best regards,

Here is the discription of the EGR valve for a 98 Trooper. It may be of some help.


Description and Operation

The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. The fuel/air mixture will be diluted and combustion temperatures reduced.

The PCM monitors the EGR actual positron and adjusts the pintle position accordingly. The uses information from the following sensors to control the pintle position:


Engine coolant temperature (ECT) sensor.
Throttle position (TP) sensor.
Mass air flow (MAF) sensor.

Thanks for the info. The I-TEC does it mechanically, but it sounds like the principle's the same: "small amounts of exhaust gas" is the definitive term. I'm guessing that with a mechanical device, like I have, the deep vacuum of heavy acceleration is offset by the increased back pressure from the exhaust so it equalizes and keeps the EGR closed.

Anyway the stumbling problem turned out to be an incredibly fouled throttle body and a maladjustment of the throttle position sensor. From an external exam it looked OK, but when I unbolted the throttle body from the common chamber there was such a heavy build-up of greasy black soot on the back of it that the throttle plates weren't closing all the way. I guess that threw off all the other settings. One afternoon and a can of carb cleaner later I'm cruising again.