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EGR revisited

8Mud

NAXJA Forum User
Location
Central Germany
Martin, Eagle, Ed from GA. among others have mentioned grief from the EGR. It has usually been my experience that they sometimes hang open and cause stalling at stops or slow cornering. Or the diaphram tears which acts as a vacume leak.
Vacume tested mine last fall, checked to make sure it seated all the way, seemed OK.
Went for a second look today, the symptoms being, hunting at idle (up and down in slow cycles a few hundred RPM), at operating temp. EGR solenoid open to vacumn. A serious flat spot at around 2000 RPM´s, with an occasional chunk, chunk, chuck or something that resemblies a crossfire, under certain throttle positions. Most often 2/3 throttle at 2000 RPM for the miss or stumble.
Found the tension on my EGR diaphram is really weak, plugged the EGR vacumn line, went for a test drive, much better low and mid range torque. I compared the tension on the diaphram, with an other EGR I have in the garage, the tension to the piston/diaphram on my 88 is seriously weak.
 
what you describe is the primary reason I bypassed my first one on my XJ. What you have, is a lack of enough vacuume- hunt for it all you want, you`ll probably never find it. I would guess you probably even have ghosting in the HVAC- as in, when you go up hill, or floor the throttle for an extended period, the defrost mode kicks on- `ala lack of suction. Downstram effects cause the IAC to have hissy fits, an the MAP to be..."confused"...both tell the TPS lies, an the TPS dont know any better.....it go`s down hill....

on my MJ now, which I still havent fixed, Ive tracked it down to the power brake diaphram, especially in cold weather- but also in warm weather. The older vehicles seem to lose vac over time-be it from wear an tear, to mini leaks somewhere-- all this adds up to low(er) than normal vac, which gets eaten up.

What we really need, is a different vacuum source other than whats provided from Mr. 4.0, that will hold "enough" without adversly haveing a negitive effect on the other controls. The EGR would stll have to be off the engine vac, but other things could possibly be routed off another vac source....been playing with the idea.
 
After disconnecting the EGR, I have much better low and mid range torque, feels like I picked up more than a few horses.
Also my shift points changed enough to notice, probably the domino scenerio you discribed, with the vacume senors, affecting the TPS values.
Amazing how not enough tension on the EGR piston can cause so much grief.
The sealing on my intake is questionable, I´ve got a replacement, along with some known injectors, a clean throttle body, associated sensors and good used exhaust manifold, I plan on installing soon. Along with a high flow cat.
Noticed near open (above 2/3 pedal) throttle vacume was a little low, thought it was just a tired motor, my compression isn´t that good, but above 125 or so.
Think the EGR opening under, to low of a vacume (early), was most of the trouble. Though I do hear a hiss or something that sounds like a diaphram relaxing, under my dash above my left leg.
I bought the XJ from a dealer, the customer refused to pay his bill, they couldn´t find the problem either, so I don´t feel too dumb.
Noticed many early Dodges (80´s) and some Chev´s have a vacume amplifier, always assumed it was to help vacume accessories function, at low vacum, idle or near WOT. I´ll have to go back a trace some vacume schematics and see where they hooked up the MAP and MAF.
 
"Think the EGR opening under, to low of a vacume (early), was most of the trouble. Though I do hear a hiss or something that sounds like a diaphram relaxing, under my dash above my left leg."

correct- thats the power brake diaphram leaking back through the firewall, and down the brake pedal input shaft- happens mostly in cold weather, or all the time if its history...most noticeable when you hit it hard with the stop foot trying to keep from hitting bling bling machines at speed. If your into correcting it, search for upgrades on the duel diaphram system in here, or through google- Ive heard some peole haveing luck useing a check valve on the vac line going to it from under hood, before the main valve on the diaphram- you still lose your power brakes, but the vac stays where its supposed to.
 
As far as additional vacuum sources is concerned, you might look at some diesels. Diesel engines, because they're unthrottled, require a mechanical vacuum pump. Many accomplish this in a way that isn't much use - Mercedes, for example, has it integrated into the front cover running off the timing chain, and VW Rabbit/Golf/Jetta diesels put the pump where the distributor would go - but I believe there are some that just drive a pump off the belts, and it might be possible to retrofit something like that. I seem to recall that some old GM diesels had a pump piggybacked on the alternator, running off an extra sheave, but I may just have imagined that.
 
Thanx for the imput guys, the 88 XJ I´ve got was seriously neglected, but low mileage. I hope to get it right (or close) one of these days, without breaking the bank, or too many sleepless nights.
Seem to be getting closer to acceptable, slowly but surely. :yelclap:
Then I can go tear it up again in the mud. :dunce:
 
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