91' Suburban problems

[Dadof2]

As I mentioned in my introduction, I have a 1991 R1500 suburban. The truck has been running fine up until approx 2 weeks ago. Two things happened:

1) Check engine light comes on but the OBD1 didn't provide any info on the Oriellys OBD1 code reader.

The truck:
R1500 254K miles
No mods
Stock tires
No obvious vacuum leaks
Engine idles fine, no hesitation, no stumbling w/ acceleration.

The main issue is the fuel mileage it has gone from 16mpg to 8 mpg.
Actions taken:
New:
fuel filter
spark plugs (gap checked before being put in)
new distributor cap
new rotor
new air filter
tires inflated to rating on sidewall
EGR appears to be good

All of this and it is still getting 8mpg.

The muffler needs to be replaced and we are going to do that when the truck goes in to have it's transmission rebuilt (no issues but the truck is our long term vehicle and we wanted to address high dollar repairs while we have the money to do it).

After messing with it some more, the "butterfly valve" in the stock air intake that houses the air filter seems to stay in the closed position. There is no piece from the exhaust manifold to the base of the air filter housing.

2) The other problem is electrical in nature:
First the cruise control went out about 3 months ago (just added that to the list of things that need to be looked at / fixed)

Then yesterday our AC/ heater fan quit working (it is a 3 week old unit bought new) and the wipers quit working.
All of the fuses in the fuse panel are good. I am assuming a relay (no power to wire coming out of relay to motor) and bought one for the fan blower motor, but Oriellys didn't show a relay for the windshield wiper motor.


Any thoughts or input would be appreciated. Tried to cover the basics first, maybe I overlooked something.

TIA

 

[RetroC10Sport]

Where in central Texas are you? My scan tool is way more useful than O'Reillys and maybe we can attack it from that angle.

It's possible there's a ground problem and that's what is causing some of your grief.

 

[350runner]

I could be wrong here but I remember something about using a fused jumper at that obd connector to get the code. Again I may be wrong

Sent from the dust in front of you!

 

[Dadof2]

Where in central Texas are you? My scan tool is way more useful than O'Reillys and maybe we can attack it from that angle.

It's possible there's a ground problem and that's what is causing some of your grief.

I am outside of Clifton in Bosque Co. Approx 2 hours from Austin and 2 hours from Dallas. Thanks for the offer to help.

 

[Dadof2]

Early morning bump before I head off to work.

 

[350runner]

Check this link it shows how to get codes http://www.chevytalk.org/fusionbb/showtopic.php?tid/273660

Sent from the dust in front of you!

 

[Quadrajet Power]

On your check engine light, my 89 had that and would run rough. It was carbon build up. I heard that was common on these in the EGR system. I ran some Lucas system cleaner through my tank and ran it wide open throttle on some drives and it helped. I didn't want to pull the intake.

 

[89Suburban]

As I mentioned in my introduction, I have a 1991 R1500 suburban. The truck has been running fine up until approx 2 weeks ago. Two things happened:

1) Check engine light comes on but the OBD1 didn't provide any info on the Oriellys OBD1 code reader.

The truck:
R1500 254K miles
No mods
Stock tires
No obvious vacuum leaks
Engine idles fine, no hesitation, no stumbling w/ acceleration.

The main issue is the fuel mileage it has gone from 16mpg to 8 mpg.
Actions taken:
New:
fuel filter
spark plugs (gap checked before being put in)
new distributor cap
new rotor
new air filter
tires inflated to rating on sidewall
EGR appears to be good

All of this and it is still getting 8mpg.

The muffler needs to be replaced and we are going to do that when the truck goes in to have it's transmission rebuilt (no issues but the truck is our long term vehicle and we wanted to address high dollar repairs while we have the money to do it).

After messing with it some more, the "butterfly valve" in the stock air intake that houses the air filter seems to stay in the closed position. There is no piece from the exhaust manifold to the base of the air filter housing.

2) The other problem is electrical in nature:
First the cruise control went out about 3 months ago (just added that to the list of things that need to be looked at / fixed)

Then yesterday our AC/ heater fan quit working (it is a 3 week old unit bought new) and the wipers quit working.
All of the fuses in the fuse panel are good. I am assuming a relay (no power to wire coming out of relay to motor) and bought one for the fan blower motor, but Oriellys didn't show a relay for the windshield wiper motor.


Any thoughts or input would be appreciated. Tried to cover the basics first, maybe I overlooked something.

TIA

1) Do an engine diagnostic with a vacuum gauge and see if you can get any codes pulled off the computer. A malfunctioning EGR could cause the drop in fuel mileage.

2) Most common cause of Cruise Control failure is a worn out switch on the turn signal stalk. Very affordable to replace. Difficulty of installation depends on how good you want it to look.

3) It's funny to me to see all these electrical failures popping up out of the blue. Maybe a grounding issue is showing itself? Simple test light procedures will help trace down the issue.

 

[Dadof2]

Thanks for all of the replies.
I got the O2 sensor changed out Friday evening and have driven just over 100 miles. It appears that my mileage has gone back up just based on the minimal movement of the fuel gauge. Next fill up I will do it based on mileage and see what I come up with.

1) Do an engine diagnostic with a vacuum gauge and see if you can get any codes pulled off the computer. A malfunctioning EGR could cause the drop in fuel mileage.

2) Most common cause of Cruise Control failure is a worn out switch on the turn signal stalk. Very affordable to replace. Difficulty of installation depends on how good you want it to look.

3) It's funny to me to see all these electrical failures popping up out of the blue. Maybe a grounding issue is showing itself? Simple test light procedures will help trace down the issue.

Would the wipers quit working because of an issue in the turn signal stalk as well? As far as the degree of difficulty, I like to keep the stock look as much as possible.

 

[89Suburban]

Thanks for all of the replies.
I got the O2 sensor changed out Friday evening and have driven just over 100 miles. It appears that my mileage has gone back up just based on the minimal movement of the fuel gauge. Next fill up I will do it based on mileage and see what I come up with.



Would the wipers quit working because of an issue in the turn signal stalk as well? As far as the degree of difficulty, I like to keep the stock look as much as possible.

See it any of this info helps:

http://www.gmsquarebody.com/forum/showthread.php?t=9913

http://www.gmsquarebody.com/forum/showthread.php?t=9916


As far as the turn signal stalk it is very easy to replace, just a real PITA to fish the cord down through the column the correct way. So I just have my cord under the outside of the column running into the dash bezel but it's not really noticeable.

 

[Dadof2]

See it any of this info helps:

http://www.gmsquarebody.com/forum/showthread.php?t=9913

http://www.gmsquarebody.com/forum/showthread.php?t=9916


As far as the turn signal stalk it is very easy to replace, just a real PITA to fish the cord down through the column the correct way. So I just have my cord under the outside of the column running into the dash bezel but it's not really noticeable.

Thanks for the links.

It appears I have a grounding issue or short in a wire. I am driving down to work yesterday and the windshield wipers just started working (Apparently, I had left the switch in the "on" position). That's good news....kinda'.

Update:
I went thru the truck again and hooked up a 12v source to the fan and it came on. Back tracked thru the wiring and didn't see anything obvious, so before really tearing into it I checked the fuses again. They looked fine, but for grins I changed the fuse out for heater/AC and the fan came on. I guess the initial fuse had a break in it, but I couldn't see where the crack was.

Cruise control I will just replace the stalk. The one on the truck now looks like it had a rough life.

Thanks for the info.

 

[89Suburban]

Thanks for the links.

It appears I have a grounding issue or short in a wire. I am driving down to work yesterday and the windshield wipers just started working (Apparently, I had left the switch in the "on" position). That's good news....kinda'.

Update:
I went thru the truck again and hooked up a 12v source to the fan and it came on. Back tracked thru the wiring and didn't see anything obvious, so before really tearing into it I checked the fuses again. They looked fine, but for grins I changed the fuse out for heater/AC and the fan came on. I guess the initial fuse had a break in it, but I couldn't see where the crack was.

Cruise control I will just replace the stalk. The one on the truck now looks like it had a rough life.

Thanks for the info.

Here is a couple of videos I made showing the cruise switch removal and installation.

http://www.gmsquarebody.com/forum/showthread.php?p=173879&highlight=cruise#post173879

I bought the new one off eBay for 15 bucks plus freight:

http://www.ebay.com/itm/CHEVY-Buick...Parts_Accessories&hash=item4872817a2a&vxp=mtr

 

[Dadof2]

Did you get the same one listed in the Ebay add? I ask because it doesn't list our trucks as compatible. Thanks for all of the help.

 

[89Suburban]

Did you get the same one listed in the Ebay add? I ask because it doesn't list our trucks as compatible. Thanks for all of the help.

If you scroll down the ad it's listed, glad to be of help:

GMC
Jimmy
(Full-Size)
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994

Pickup (C/K)
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994

S15/Sonoma Pickup
1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993

S15 Jimmy
1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993

Suburban
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994

 

[Dadof2]

Cruise Control switch is on it's way.

My mileage is back up after the 02 sensor change out.

Fan is working intermittently, so I am assuming a grounding issue or a broken wire. I can live with it for now.

Next up is turning my attention back to the 81 C20 and getting it up and running again.