Unplug EGR, runs great, Plug in, hesitates runs poorly

The needs of the many · Aug 2, 2023

88 Foxbody. Runs poorly and hesitates with EGR connected. Unplug EGR, car runs well. Runs a little hot unplugged just past the middle according to the gauge. Used premium, car gauge normal.
Work performed: replaced EGR, EGR solenoid, and EGR position sensor. Hole in the muffler. Smell the exhaust, but no "ROTTEN EGG" smell. No white smoke from the tailpipe. Have a laser thermometer. How hot should CAT be before and aft? Very confused...thanks.

Trogdor · Aug 2, 2023

Are both cats the same temperature?

The needs of the many · Aug 2, 2023

will check. I thought there were actually three- left, right, and downstream.

Trogdor · Aug 2, 2023

Stock exhaust has 4 cats. Check temperature between banks on the same location.

Have you checked for codes?

Is fuel pressure at idle between 32 and 42 psi?

Is base timing where it's supposed to be?

Bad gas?

AeroCoupe · Aug 3, 2023

Plugged EGR valve or EGR spacer?

The needs of the many · Aug 3, 2023

Hello gentlemen:
Today, I had the muffers that had holes in them replaced. Full power restored; runs cool, but when connected to EGR, still issues with hesitation. If the EGR solenoid was hooked up backward (plastic hoses) and then corrected, could I have ruined it? The Smog guy told me over the phone that it sounds like it is stuck open.
Tomorrow, I will replace plastic or nylon hoses (brittle) and hope for the best. Those plastic hoses get the openings narrowed like arteriosclerosis and actually shrink in diameter, and I'm hoping that could contribute to my issue. I did check the hose vacuum w/o a vacuum gauge, and the vacuum was very little.

Mustang5L5 · Aug 4, 2023

Does sound to me like the EGR is stuck open. It's only supposed to open during cruise. EGR closed at idle and WOT so you wouldn't see any vac then.

When you say you unplug it, what are you unplugging? The electrical connector or removing vac?

I don't think you ruined the solenoid. The vac hoses could be hooked up either way and it will function as the solenoid just opens and closes and isn't directional.

The needs of the many · Aug 4, 2023

Thanks for getting back to me, Mustang5L5. I disconnected the hose from EVR to the EGR (saucer)valve. BTW, before I continue, I pulled the VAC line off the VAC solenoid and blew threw it. I did not hear the air going back into the TB and it seemed blocked somewhere between all my plastic hose repairs and the one rubber plug that attaches under the plenum. I cannot remove the rubber plug with my fingers, which tells me the darn thing probably melted over the port and I am going to have to "chisel" it off and replace that entire plastic POS vacuum hose with A good 'ol rubber one.
Getting back to answer your question: After disconnecting this hose, (and putting a screw in it) the car seemed to run fine- but the temp gauge reported running at a hotter temp, going beyond the typical "center position" and in the 90-degree weather it did that regardless.
My fear was running in this method the PCM would advance my timing and lean out the fuel, so I tried to compensate by running premium fuel.
2nd note, I had numerous holes in the pipe and mufflers below the CAT, and yesterday, I replaced the phony "dual exhaust" that was "y'ed off" from A SINGLE pipe below cat (there was never a dual exhaust" and opted for a single muffler and the vehicle is now very quiet and has better performance.
I want to pass smog so I have to fix the EGR system and the components are all new and made by Standard Ignition.
My condition occurs when plugging that hose back into the EGR it hesitates and loses power. It only seems to run OK with that damn thing disconnected. What to do? Thanks again for getting back to me.

Mindseye007 · Oct 15, 2023

The needs of the many said:
Thanks for getting back to me, Mustang5L5. I disconnected the hose from EVR to the EGR (saucer)valve. BTW, before I continue, I pulled the VAC line off the VAC solenoid and blew threw it. I did not hear the air going back into the TB and it seemed blocked somewhere between all my plastic hose repairs and the one rubber plug that attaches under the plenum. I cannot remove the rubber plug with my fingers, which tells me the darn thing probably melted over the port and I am going to have to "chisel" it off and replace that entire plastic POS vacuum hose with A good 'ol rubber one.
Getting back to answer your question: After disconnecting this hose, (and putting a screw in it) the car seemed to run fine- but the temp gauge reported running at a hotter temp, going beyond the typical "center position" and in the 90-degree weather it did that regardless.
My fear was running in this method the PCM would advance my timing and lean out the fuel, so I tried to compensate by running premium fuel.
2nd note, I had numerous holes in the pipe and mufflers below the CAT, and yesterday, I replaced the phony "dual exhaust" that was "y'ed off" from A SINGLE pipe below cat (there was never a dual exhaust" and opted for a single muffler and the vehicle is now very quiet and has better performance.
I want to pass smog so I have to fix the EGR system and the components are all new and made by Standard Ignition.
My condition occurs when plugging that hose back into the EGR it hesitates and loses power. It only seems to run OK with that damn thing disconnected. What to do? Thanks again for getting back to me.

try pulling codes see what you get...do you have a code tester?

Noobz347 · Oct 16, 2023

It's funny sometimes how these issues pop up in groups on Stangnet. I just posted this to another member 30 minutes ago:

Amazon product ASIN B07471TKRF

That aside, I don't know what you've heard about fuel octane but it doesn't make up in any way for a lean condition.

Is your 88 a Speed Density or Mass Air car? A vacuum leak will effect either system but I can't think of a single in stance where either system would lean out fuel or advance timing as temperature rose. I don't consider this scenario to be of concern.

Definitely keep chiseling away at those old vacuum hoses. If they even "look" suspect, swap them out. Let us know what you find with the tests above.

The needs of the many · Oct 16, 2023

Mindseye007 said:
try pulling codes see what you get...do you have a code tester?

Thank

Mindseye007 said:
try pulling codes see what you get...do you have a code tester?

Thank you for getting back to me. I have a single diagnostic plug in the right position on the driver's side. The car came without a single (ground) plug.
I have had to guess and become my own mechanic. (Like the rest of us) I HAVE replaced the EGR valve, the EGR position sensor, and the EGR solenoid. I replaced the brittle vacuum hoses in the EGR circuit. The CAT has been replaced and the faulty exhaust system has been replaced. I did a vacuum test with a cigar. Thirty seconds after starting the car, the car starts to drop RPM or "lean out" and the car runs rough for close to a minute and hesitates and loses power badly for close to a minute following both a hot or cold start. The computer "corrects" the condition and the car runs properly after this mishap minuet as if the problem did not exist. I got rid of my cold air intake and replaced it with the factory intake which does NOT have a mass air flow sensor from the factory. Any help you can provide will be appreciated.

Unplug EGR, runs great, Plug in, hesitates runs poorly

The needs of the many

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Trogdor

The needs of the many

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Trogdor

AeroCoupe

lube between the nut and the face. I know my lubes

The needs of the many

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Mustang5L5

That is…until I whipped out my Bissell

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Mindseye007

10 years still blowing strong

Noobz347

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Unplug EGR, runs great, Plug in, hesitates runs poorly

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