91 GM Engine Miss with Code 33

[Art Gladfelter]

Greetings,

Have a '91 GM 5.0L engine with 140K Miles...that surges & runs rough when NOT accelerating...does it in 3rd gear...so it is not the auto tranny. Idle & top end power are great.

Got 2 digit code of 33..."EGR valve not opening;insufficient flow detected"

So...I cleaned & checked EGR valve...seemed to work OK on bench with about 4" of vacuum. I then disconnected vacuum on EGR valve(plugged vacuum line), drove car and missing/surging went away...but there was a lack of power and acceleration.

Did electrical check of Throttle Position Sensor(TPS)...it checked out OK on the bench with a smooth change in resistance.

Replaced Electronic Vacuum Regulator(EVR) that controls the amount of vacuum to EGR valve. Engine still surges and runs rough after reaching driving or floating speed. Fuel filter, air filter, plugs, rotor, cap, etc. were all replaced and/or seemed to be OK. I have NOT changed PCV valve or the small air breather screen at the back of the engine.

So...My thanks in advance to anyone who can give me any suggestions to cure an engine miss at cruising speed with code 33.

Art Gladfelter

[jimmytroanoke]

Originally Posted by Art Gladfelter

Greetings,

Have a '91 GM 5.0L engine with 140K Miles...that surges & runs rough when NOT accelerating...does it in 3rd gear...so it is not the auto tranny. Idle & top end power are great.

Got 2 digit code of 33..."EGR valve not opening;insufficient flow detected"

So...I cleaned & checked EGR valve...seemed to work OK on bench with about 4" of vacuum. I then disconnected vacuum on EGR valve(plugged vacuum line), drove car and missing/surging went away...but there was a lack of power and acceleration.

Did electrical check of Throttle Position Sensor(TPS)...it checked out OK on the bench with a smooth change in resistance.

Replaced Electronic Vacuum Regulator(EVR) that controls the amount of vacuum to EGR valve. Engine still surges and runs rough after reaching driving or floating speed. Fuel filter, air filter, plugs, rotor, cap, etc. were all replaced and/or seemed to be OK. I have NOT changed PCV valve or the small air breather screen at the back of the engine.

So...My thanks in advance to anyone who can give me any suggestions to cure an engine miss at cruising speed with code 33.

Art Gladfelter

Are you sure on the code and it's meaning. The reason I ask is it sounds more like the egr is stuck open from your symptoms. The surging problem sounds like a vacuum leak. Spray some starting fluid or carb cleaner around your intake and all the hoses with the car idling and listen for a change in the idle. If the leak is on something that ties to the same vacuum source as your egr system that may cause a false egr code. Does the car spark knock? With insufficient EGR that is usually the #1 symptom. I am sure someone else will chime in with more. You also may have a malfunctioning or sticking IAC valve.

[Art Gladfelter]

Thanks...Jimmy...for your reply.

I couldn't find a vacuum leak in spraying starting fluid.

The engine does NOT knock or ping...it
just misses when floating at 30 plus MPH....pretty smooth on acceleration & deceleration.

On second test of codes, I got a code 34, EGR valve positions sensor...but I now noticed this test was to be done with engine running, which I did not do. Anyway, I put another working/good EGR position sensor on '91 GM and this did NOT solve the missing problem.

You mentioned the IAC valve. Is there a way I can check this on or off the vehicle?? I see Ford has two(2) listed: CX-1823($58.79) and CX-1824($63.79).

Could a sticking/faulty Canister Purge Valve be at fault??
Parts list shows four(4) Purge Valves connected to one wiring harness & connector.

Take care.

Art Gladfelter

[Jagman26]

Hey Art, how's it going? My name is Jaison, fairly new to this forum, nice to meet you. I was having a similar problem with my 95 GM, kept throwing a code for insufficient egr flow, and I went through all the same steps you did, checked all sensors, vacuum lines, even checked the egr transfer pipe. I finally found the problem to be on the intake where the egr enters, the passage way was completely clogged. It sounds like you are familiar with egr and the basic reasoning behind it, but maybe I can help clear things up for you. Basically what the egr does is take up space in the cylinder so that less fuel is used, helping to increase fuel mileage, and decrease emissions and is introduced at cruising speed to accomplish this process. However, you do not want egr at start up, nor on accerlation. I hope I was able to lead you in the right direction. Let me know how it goes.

Jaison

[Art Gladfelter]

Hi Jaison,

I'm also new to this form. Thanks for your response.

You said you found the "problem to be on the INTAKE where EGR enters, the passage was completely blocked..."

Was the clogged passage on the EGR valve or where the EGR valve mates to the throttle body?? Maybe I'm not looking in the right place to clean out some carbon??? Is there some tube(s) that I'm not aware of??

Thanks again!

Art Gladfelter

[jimmytroanoke]

Originally Posted by Art Gladfelter

Hi Jaison,

I'm also new to this form. Thanks for your response.

You said you found the "problem to be on the INTAKE where EGR enters, the passage was completely blocked..."

Was the clogged passage on the EGR valve or where the EGR valve mates to the throttle body?? Maybe I'm not looking in the right place to clean out some carbon??? Is there some tube(s) that I'm not aware of??

Thanks again!

Art Gladfelter

I'm not sure where the EGR attaches to your engine, but on most it is usually on the intake somewhere. There are generally some small passages between where the egr bolts on going to the intake stream. These quite frequently get clogged ith carbon and oily sludge. On my truck I had to chase them with wire before 100# of compressed air would blow them out! If you can remove the throttle body and get to where they come into the intake catch the gunk with a rag to keep it from going into the engine.

A sticking purge valve could act like a vacuum leak, but I would think it would throw a code.
Without a shop manual, I could not tell you how to check the IAC, electically. You could remove it tho and see if it is carboned up, and not moving freely. Sometimes they are cleanable.

Go ahead and change the PCV as well. Use a Motorcraft one.

[Art Gladfelter]

Greetings Jimmy & Jaison,

Cleaned carbon from EGR valve spacer. Also removed IAC valve, cleaned it, and solenoid was operative. (One needs to use a current limiting 6-12 Volt DC power supply-to assure correct polarity- to check solenoid because of internal protection diode) Still had engine miss when floating 30-60 MPH.

I still need to change the PCV valve.

Also, are there any passages that would need to be cleaned Under the UPPER MANIFOLD COVER??? This is the plate with the FORD emblem & 5.0 LITERS EFI letters....held on with four(4) torx screws.

Still trying. Thanks for all your suggestions.

Art Gladfelter

[jimmytroanoke]

Originally Posted by Art Gladfelter

Greetings Jimmy & Jaison,

Cleaned carbon from EGR valve spacer. Also removed IAC valve, cleaned it, and solenoid was operative. (One needs to use a current limiting 6-12 Volt DC power supply-to assure correct polarity- to check solenoid because of internal protection diode) Still had engine miss when floating 30-60 MPH.

I still need to change the PCV valve.

Also, are there any passages that would need to be cleaned Under the UPPER MANIFOLD COVER??? This is the plate with the FORD emblem & 5.0 LITERS EFI letters....held on with four(4) torx screws.

Still trying. Thanks for all your suggestions.

Art Gladfelter

You are welcome! When you had the EGR off, did you run a wire or something into the passages in the intake itself to make sure they were open? There needs to be a clear passage to the intake stream. That said, I know you said you tested your EGR valve itself. Sounded like you have a handheld vacuum pump. When you tested it, did it hold the vacuum? I also have no idea what the opening spec is. Generally egr is used at light throttle, high vacuum operations. If your valve is opening at 4 in. that is pretty low(IMO). Maybe it is over opening due to a weak spring. Try posting your questions with details on what you have tried at www.flatratetech.com in the automotive support forums, ford section. This site is staffed by Ford techs and they can probably help you out.

[Art Gladfelter]

Greetings Jimmy & Jaison,

A big thank YOU to both of you for all your suggestions.
Flatratetech.com is a great web site.

Plugs were in '91 GM for about 20K from 120-140K miles...I didn't think they needed to be changed. Plugs 1 to 7 looked great, but #8 had a big glob of carbon shorting out the electrodes. I showed fouled plug to a Master Tech. and he felt it may have been just a piece of carbon that got lodged in #8. Oil conslumption is not excessive...about a quart to 2K-2.5K miles. Check of #8 ignition wire seemed to be OK @ 10K ohms total. My wife is primary driver and she takes 3 or 4 trips each week for a distace of only 2 block .... and this may have been part of the problem. I'll try to post a photo showing a typical good plug along side of the fouled #8 plug.

Case Closed! Got to start working on slight hesitation in slant 6 in '68 Dart.

Thanks again. Take care.

Art G.

[jimmytroanoke]

Originally Posted by Art Gladfelter

Greetings Jimmy & Jaison,

A big thank YOU to both of you for all your suggestions.
Flatratetech.com is a great web site.

Case Closed! Got to start working on slight hesitation in slant 6 in '68 Dart.

Thanks again. Take care.

Art G.

Glad you found the trouble. Strange that it threw an EGR code and not a misfire code. Did it clear itself or did you clear it. Good luck on the ol' 225-1 barrel! What I would give to work on something like that again! I've got a '68 Olds 442 convertible if I ever get time to work on it again!.

[Art Gladfelter]

Hi Jimmy,

I didn't clear code 33 or 34....but maybe I should do it??
Service Manager at Ford garage said newer Fords would show a code for a shorted/fouled spark plug.

I'll let you go...hope you get some time to work on that '68 Olds...you probably will not even have to go thru an emission test!!!

Art G.

PS-For some reason, I was unable to attach/send the photo of fowled plug.

[jimmytroanoke]

[quote=Art Gladfelter]Hi Jimmy,

I didn't clear code 33 or 34....but maybe I should do it??
Service Manager at Ford garage said newer Fords would show a code for a shorted/fouled spark plug.

Art G.

QUOTE]
Do you still have an check engine light? If it has gone out it has probably cleared itself.

No smog checks here! For the immediate future anyway, anything goes!

Jim

[Art Gladfelter]

Check Engine light never came on for code 33 or 34,
but did flash the correct code when I was doing the self test.
Check Engine light is now"Off"...car is running great & my wife drove it about 10 miles to work this morning.

Take care.
Art G.