When you say you have "gone through" the fuel and ignition systems what exactly did you do? If you're still running the lousy OEM damper it's very possible the outer ring has slipped into a retarded position which means your timing is also in a retarded position and the engine is having an awful time running. Based on age alone I recommend replacing any OEM damper with a modern damper that is known to be accurate and then go from there.

 

you have to use ported vacuum for egr. if you use manifold vac, egr will open at idle (when it isn't supposed to) and run like, well yours does. ported vac and thermal switch on thermo housing. at least that is where my 75's is. and i just saw a buncha vac hoses unhooked on mine, so mebbe that is why mine no run so good...egr block-off plate is another idea, but your year you may need to go see the emissions guy...

 

I plugged my 78 L-82 EGR back in 1983 since it made the car run like crap and some time later removed the EGR valve permanently using a an EGR block off plate.

I just went through this EGR issue with my 100% stock 1994 Mustang GT 5.0 (31,000 miles) except BBK shorty Headers, Magnaflow high flow cats (4) X pipe and Magnaflow cat back mufflers-2.5 inch system and K&N cold air package. The Ford system is different than the 78 EGR with an electronic sensor detecting EGR movement linked to the check engine light, EGR vacuum operation under all engine conditions except idle-High vacuum closed, lower vacuum EGR valve open. The issue was that when the engine was hot, it would ping and rattle the valves under moderate throttle to WOT and mid to high RPM operation. I made sure the timing was factory correct, plugs were good, and wires were new...no change. Changed to 89 octane gas which helped but did not eliminate the pinging. Tried to keep it 100% factory correct but to no avail so tried disconnecting the electronic nanny-check engine light, removing vaccum connection from EGR-check engine light and finally decided introducing 400-500 degree "dirty" exhaust did not make sense and would effect engine performance. I have never subscribed to the notion that EGR gases have a "cooling" effect on the intake charge and dirty hot exhaust gas was not detrimental to the engine's driveability, performance, and mileage. Went to Home Depot and capped the exhaust header source and the EGR inlet but left everything else intact-no check engine light. Result: Just passed state emissions inspection with zero effect on HC/NO at 2,500 RPM-ZERO (PPM and % are so low its laughable-HC was 6 PPM out of limit of 220 PPM!, engine has not pinged once since the block off of the EGR, throttle response is noticeably crisper, engine temp is noticeably LOWER on the gauge in all types of driving and gas mileage has gone UP along with power mid-high RPM. Only took me 21 years to solve the problem

Get rid of it......worthless crude emissions junk

 

First of all the exhaust gasses don't "cool" the intake charge but rather dilutes it to reduce combustion temperatures.

To learn what the EGR actually does I recommend Googling "EGR Valve Wikipedia".

 

I know how an EGR works and what I said was "EGR gases have a "cooling" effect on the intake charge"...Clearly in my example with the Mustang above, there is no "cooling effect" needed since the combustion chamber temps clearly are lower with no EGR and the elimination of any detectable spark knock which would not have occurred if the the EGR delete RAISED the combustion chamber temp...reality versus "theory".

 

The EGR on the early cars was called a ported EGR. This switch mentioned above is the ported vacuum switch mounted on the front of the intake. This switch is what controls the vacuum to the egr valve so a malfunction at the switch will keep the valve from working.





Willcox

 

EGR has no effect on HC or CO and a faulty EGR wont show up on a 2 speed unloaded type smog test. I guarantee your NOx emissions would be sky high on a loaded/dyno type smog check.

 

There was no change in NOx emissions which I mentioned above and the inspection for pre OBDII cars in my state requires the car to be on a roller and drive a course, monitoring the emissions the whole way-not a static idle and 2,500 rpm emissions test. I am well aware that EGR does not effect HC/CO. Any other comments?

When my 78 was emissions inspected back in the early 80's with no EGR it always passed NOx as well.

Again reality versus theory.

 

Not really other than if you did indeed pass a loaded smog test w/o a operable EGR, either your cat(s) have a very strong 3rd bed or your state has a high cutoff level. I've been a smog /driveability tech for 20 years and I have never seen a car be able to pass a ASM type smog test with a malfunctioning EGR system. Of course I'm in California, were a bit stricter and just the fact that you modified your EGR system would be a instant failure here.

 

Interestingly, the 94 mustang GT is a California car originally with 4 cats-2 pre cats and 2 full cats. I believe the 49 state GT's only had 2 full cats. The only requirement (not the law) for my state emissions inspection is that the car passes a loaded smog/driveability test...there is not inspection that each and every emissions component be present and operating. As long as no check engine light, good to go...