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Author Topic:   High HC in Exhaust
ddenton749
Gearhead

Posts: 377
From: Kennett Square, PA, USA
Registered: Apr 2004

posted 10-04-2004 12:33 PM     Click Here to See the Profile for ddenton749   Click Here to Email ddenton749     Edit/Delete Message   Reply w/Quote
My '91 LX 5.0 Vert won't pass PA emissions inspection. The first time it was tested it had high HC, high NOX, and normal CO. I replaced the O2 sensors and the cats. (The car has 167,000 miles on it)

The second time it was tested it just had high HC, even with the SPOUT unplugged.

The car is running very rich. I retrieved the codes (KOEO) on Sunday and got:

34 - EVP voltage above closed limit
66 - MAF circuit below minimum voltage

I checked the connections and inspected the MAF - all look ok. I cleared the codes, ran the car again and then put the code reader back on. I got the 34 again but not 66.

I didn't do the KOER test because I wanted to fix the EVP problem first, then proceed with the rest of the diagnostics.

Does anyone have an idea what would cause this excessively rich condition? I don't want to continue to run the car for fear of wiping out the new cats.

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'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club

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quick50stng
Journeyman

Posts: 58
From: Athens,GA. USA
Registered: Sep 2004

posted 10-04-2004 01:39 PM     Click Here to See the Profile for quick50stng   Click Here to Email quick50stng     Edit/Delete Message   Reply w/Quote
Any there any other modifications to your car?

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ddenton749
Gearhead

Posts: 377
From: Kennett Square, PA, USA
Registered: Apr 2004

posted 10-04-2004 01:41 PM     Click Here to See the Profile for ddenton749   Click Here to Email ddenton749     Edit/Delete Message   Reply w/Quote
It's as stock as the day it rolled off of the line.

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'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club

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ddenton749
Gearhead

Posts: 377
From: Kennett Square, PA, USA
Registered: Apr 2004

posted 10-04-2004 01:44 PM     Click Here to See the Profile for ddenton749   Click Here to Email ddenton749     Edit/Delete Message   Reply w/Quote
I was just reading that the EVP sends a signal back to the ECM indicating EGR position. The ECM in turn uses this signal to reduce the amount of fuel flow through the injectors because there is less air (more exhaust gasses) when the EGR is open. Could this cause really high HC in the exhaust? (Rich condition?)

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'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club

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73torinoqcode
Gearhead

Posts: 388
From: Buffalo,NY,USA
Registered: Jun 2003

posted 10-04-2004 08:07 PM     Click Here to See the Profile for 73torinoqcode   Click Here to Email 73torinoqcode     Edit/Delete Message   Reply w/Quote
How about a bad injector?

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GTRocks
Gearhead

Posts: 3652
From: Lusby, MD
Registered: Jun 99

posted 10-04-2004 10:07 PM     Click Here to See the Profile for GTRocks   Click Here to Email GTRocks     Edit/Delete Message   Reply w/Quote
Did you clean the MAF? If you disconnect the MAF and look inside, there are two small wires that hang down inside. They run current through them and sense the resistance of the circuit, which can be calculated to determine the air flow coming in to the intake. This measurement is then used to determine the air/fuel ratio. Particularly if you have an oil (K&N type) filter, particles will build up on those two little wires. This will cause a false resistance reading and hence your car will run rich. Mine got so bad it was actually backfiring. Take the MAF off and clean those two little wires with carb cleaner and a Q-tip (GENTLY!!! ) Put her all back together and you'll find a few extra horses you've been missing too.

That's my guess!

[This message has been edited by GTRocks (edited 10-04-2004).]

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ddenton749
Gearhead

Posts: 377
From: Kennett Square, PA, USA
Registered: Apr 2004

posted 10-05-2004 12:51 AM     Click Here to See the Profile for ddenton749   Click Here to Email ddenton749     Edit/Delete Message   Reply w/Quote
GT-
Yes, the MAF is clean. I had it off of the car and apart. I cleand the body of the venturi and cleaned the wires on the sensor with Q-tips. The air filter is the stock paper element.

I put it back together and I really don't think it made any difference. The exhaust still smells rich. Tomorrow night (Tues) I'm going to test the resistance of the EVP sensor since that's the trouble code I'm getting. When I have no more codes in the KOEO test I'll move on to the KEOR part of the test.

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club

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ddenton749
Gearhead

Posts: 377
From: Kennett Square, PA, USA
Registered: Apr 2004

posted 10-05-2004 12:54 AM     Click Here to See the Profile for ddenton749   Click Here to Email ddenton749     Edit/Delete Message   Reply w/Quote
73-
I bought a fuel pressure guage so I can see if I have any fuel pressure leak down which might indicate a leaky injector. I think if I had one or two leaky ones it would show up as a rough idle.

Basically the car runs great except for the high HC (rich) exhaust.

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'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club

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Velocity0
Gearhead

Posts: 330
From: Burnaby, BC Canada
Registered: Apr 2001

posted 10-05-2004 02:23 AM     Click Here to See the Profile for Velocity0   Click Here to Email Velocity0     Edit/Delete Message   Reply w/Quote
Does it have high HC while driving, or just idle? or both?

Have you checked/replaced the usual stuff?
Plugs, cap rotor wires etc.
High HC is usually just unburned gas after all.
If your ignition isn't up to snuff, that would cause it too. Even though it runs fine.

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ddenton749
Gearhead

Posts: 377
From: Kennett Square, PA, USA
Registered: Apr 2004

posted 10-05-2004 07:37 AM     Click Here to See the Profile for ddenton749   Click Here to Email ddenton749     Edit/Delete Message   Reply w/Quote
Velocity-
The exhaust smells rich at idle. The PA emissions test is done on a dyno with the car at 15 mph.

New cap, rotor, plugs, air filter and fuel filter. I don't know how old the wires are. I had the intake off to replace valve cover gaskets and inspected very closely for vacuum leaks and didn't find anything. It's definitely dumping unburned fuel out the exhaust.

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club

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73torinoqcode
Gearhead

Posts: 388
From: Buffalo,NY,USA
Registered: Jun 2003

posted 10-05-2004 08:42 PM     Click Here to See the Profile for 73torinoqcode   Click Here to Email 73torinoqcode     Edit/Delete Message   Reply w/Quote
I have heard to let the car run for a long time before you hook it up to the smogger. Lock it and even when you wait let the car run. The hotter the better. Will it go away when up to temp for a while? My 92 runs a bit rich also but we have no Smog here. Maybe do some searches on how to pass emission testing if all else fails.

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ddenton749
Gearhead

Posts: 377
From: Kennett Square, PA, USA
Registered: Apr 2004

posted 10-06-2004 08:24 AM     Click Here to See the Profile for ddenton749   Click Here to Email ddenton749     Edit/Delete Message   Reply w/Quote
73-
I'm going to try a new MAF sensor today. At the place where I'm going for inspection, the owner is a classic Mustang guy, and the mechanic has a '96 Mustang vert and used to own a modified '90 GT. They're the ones telling me to go for the MAF sensor, saying that it should make a big difference. Of course, they said the same thing about the O2 sensors, cats, and EVP sensor.

I back-probed the MAF. I got battery voltage at the VPWR terminal. The MAF SIG RTN was 0.01 volts and the MAF SIG was around 3 volts. Apparently the 0.01 volts is what is giving me Code 66 (in the post above).

We shall see later today.

Oh yeah, the fuel pressure running is 32 psig. However, it drops to zero as soon as I shut off the engine. I was told that is due to a leaky check valve in the fuel pump. Any comments on that one?

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club

[This message has been edited by ddenton749 (edited 10-06-2004).]

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BLUE
Gearhead

Posts: 173
From: COLLINSVILLE, IL
Registered: May 2002

posted 10-06-2004 09:07 PM     Click Here to See the Profile for BLUE     Edit/Delete Message   Reply w/Quote
havent tried this myself but i read that you can unplug #1 injector then that cylinder acts as an air pump?

also heard people mixing alcohol with their gas.

any thoughts on these ideas?

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ddenton749
Gearhead

Posts: 377
From: Kennett Square, PA, USA
Registered: Apr 2004

posted 10-06-2004 09:42 PM     Click Here to See the Profile for ddenton749   Click Here to Email ddenton749     Edit/Delete Message   Reply w/Quote
Hey Blue-

I haven't thought of those...but desperate times require desperate measures...

I would still like to get the car right. I don't want to wipe the new cats running rich all the time. Besides, it seems to be a real gas pig.

D

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club

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ddenton749
Gearhead

Posts: 377
From: Kennett Square, PA, USA
Registered: Apr 2004

posted 10-07-2004 02:23 PM     Click Here to See the Profile for ddenton749   Click Here to Email ddenton749     Edit/Delete Message   Reply w/Quote
I finally got the car to pass emissions inspection today - barely. it took three more tries and the HC was still high. The first test the readings were 355 and should be less than 275. (Divide these numbers by 5 for actual readings.)

We tried it a second time and it passed. The Tech seems to think that the EGR isn't working right and is causing the erroneous reading from the EVP sensor. This may cause the computer to think the EGR is open and the computer tries to close it, when in actuality it should be open.

I'll replace the EGR in a couple of weeks (next payday)

Thanks to all for your help.

D-

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'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club

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Moneymaker
Administrator

Posts: 26242
From: Lyons, IL, USA
Registered: May 99

posted 10-07-2004 03:27 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Take your VIN and call or go to a friendly F/L/M dealer and have it run for recall campains.
In 91-92 there was a TSB and recall on 5.0 cars for a faulty o2 sensor harness.
Also, there was a trick IAC motor spacer with adjustable air bleeds specifically for idle lean out that was installed.

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
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NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,& '04
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ddenton749
Gearhead

Posts: 377
From: Kennett Square, PA, USA
Registered: Apr 2004

posted 10-07-2004 03:50 PM     Click Here to See the Profile for ddenton749   Click Here to Email ddenton749     Edit/Delete Message   Reply w/Quote
Thanks, Alex. Interesting. I think I'll do that. The guys at the local Ford dealer are my new best friends

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'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club

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