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Topic: EGR troubleshooting help needed... (Read 2483 times) previous topic - next topic

EGR troubleshooting help needed...

1987 3.8L Thunderbird - 230,000 miles

I've had the EGR bypassed since I've owned the car (2+ years). The 'bird runs quite well without it. Once in a while, there is a bit of bucking during deceleration, but this may be caused by my worn our rear-end.

When the EGR is hooked up, the car will exhibit very minor bucking during stead-state cruise. It is the worst at ~45 mph. Also, if I let off the gas real quick, the car will buck harshly once/twice. It also feels like the car is missing 1.5 cylinders. Some hills require a downshift to hold speed where it wouldn't with the EGR bypassed. Also, the gas mileage is noticeably worse.

I've tested the EGRV and EGRC solenoids and they both passed. The EVP response is linear with no hiccups. The EGR valve itself holds vacuum and opens fully at ~4" Hg.

With the EGR hooked up, the EEC returns no codes. Bypass it and it gives a 34 (KOER).

The only thing I know that isn't up to snuff is the TPS idle voltage. It is ~1.15V. I haven't adjusted it because it is a pain in the butt to do so. I wouldn't think this would cause the EGR problems though; as long as the TPS is "open" and not changing voltage, the EEC isn't using it to modify any tables.

Anyone have any ideas before I start throwing expensive new parts on?

EGR troubleshooting help needed...

Reply #1 –
This thread is now open to rampant speculation and hearsay.

EGR troubleshooting help needed...

Reply #2 –
My 5.0 HO exhibited some similar symtoms a few months back.  I had a spare TPS laying around from my old 5.0(it was the original 1988 sensor with '92k on it and about a year sitting) and it was like the car had new life breathed into it.  It's a cheap enough part that might just be worth replacing.  I'm now hooked on factory ford replacement parts when it comes to sensors/electronics.  But that's just my two cents.

Good luck,
Don
Project 3G: Grandpa Grocery Getter-'85 Crown Vic LTD 2-door, 351W with heavily ported/polished GT40 heads, heavily ported/polished Typhoon Power Plus upper & lower intake, Comp Cams 265DEH retarded 1*, FAST EZ-EFI, HD T5, 8.8" 3.73 trac lock with extra clutches, 3G alt. swap, '99 CVPI front brakes, '09 CVPI rear disc brakes, '00 CVPI booster&m/c + wilwood adj prop valve.

Parted & Gone-'88 T-bird Sport, 351W swap, ported GT40 heads

EGR troubleshooting help needed...

Reply #3 –
My '84 3.8L T-Bird has been doing the same thing for years. There is a TSB that says the EGR Vent soleniod is not doing its thing because dirt is clogging the air hole. If air can't get in to release the vacuum the valve will stay open.
I replaced the EGR solenoids because one went open circuit but it didn't fix the bucking problem for me.
Over the years I have replaced the valve and the position sensor for other reasons with no effect on the bucking problem.
I have wondered if there was any connection to the smog pump/thermactor pumping fresh air into the exhaust manifold but I have never done anything to prove or disprove it.

EGR troubleshooting help needed...

Reply #4 –
If your AIR system is operating properly,  the Thermactor is sending air to the catalytic converter or venting it to atmosphere any time the EGR is active.

EGR troubleshooting help needed...

Reply #5 –
Maybe I'll revisit it again when warm weather gets here. Meanwhile a golf tee in the end of the EGR vacuum line will have to do.
The car didn't do it when it was new, so something obviously has changed.

EGR troubleshooting help needed...

Reply #6 –
I see in the shop manual that the vacuum line that opens the EGR valve also opens the carbon canister purge valve. The "purge" hose hooks to the top of the PCV valve.

Just something to wonder about.

EGR troubleshooting help needed...

Reply #7 –
Just so you know your not the only one Jeremy, my 88 has had a code 33 since I got it a year ago. Differn't thing though, mine runs fine. Kinda the opposite of yours. I've never unhooked the EGR system in any way. My car doesn't have an EGR position sensor like other cars. Nothing is on top of the valve. It has the little pressure sensor, wich specs out fine on a multi meter with a vacume pump. Still can't get that  code 33 to go away.
 
 
*edit*  forgot to mention the code 34 that I get.  One for koeo and one for koer.
One 88

EGR troubleshooting help needed...

Reply #8 –
Anyone have the testing specs for the EGR valve / Canister Purge valve?

The EGR valve moves to a fully open position by 4" vacuum.

I also tested the TPS. It was .827V with the ISC retracted.

EGR troubleshooting help needed...

Reply #9 –
I checked an old EGR valve I  have on the shelf and it opens all the way with 4" of vacuum also. This one sometimes doesn't open smoothly. It will "pop" open at 2'' of vacuum.
The only check for it in the shop manual is a vacuum leak-down test.
"Apply 5-6 inches Hg. to the valve. The vacuum should not drop more than 1 inch in 30 seconds."
My valve flunks this test.

The only test for the purge valve is it is closed with no vacuum to the "signal vacuum port" and open with vacuum.

The hose connector plugged into the canistor has two hose connections. One to the purge valve and the other to the gas tank.
So when the valve opens it sucks fumes from the canistor and the gas tank.

EGR troubleshooting help needed...

Reply #10 –
I replaced the EGR valve and position sensor (Motorcraft) while repairing the MVAC reservoir...problem fixed.

All the old EGR parts passed the tests but were still bad.

EGR troubleshooting help needed...

Reply #11 –
Good deal!! Sounds like I have been making some bad assumptions.
 

EGR troubleshooting help needed...

Reply #12 –
I don't think you've made any bad assumptions. If you've replaced your solenoids, valve, and position sensor...I would suspect clogged passages.
When I R&R'd my lower intake, I found the EGR passages almost totally clogged. Cleaning them didn't fix my problem as the valve and/or sensor was still bad.

EGR troubleshooting help needed...

Reply #13 –
I had the throttle body off summer before last and the passages were not too bad. Seems like clogged passages would be the same as the valve never opening.
Mine seems to act up more in warm weather but given what seems to be the same conditions on another day it may not fail.