Engine surges and stalls at cold idle


PetroleumJunkie412

2.9 Mafia
Supporting Member
TRS 20th Anniversary
Joined
Oct 31, 2018
Messages
2,722
Reaction score
1,940
Points
113
Location
Pittsburgh, PA
Vehicle Year
1988
Make / Model
Ranger
Engine Type
2.9 V6
Transmission
Manual
2WD / 4WD
4WD
Ok. Update. To answer some questions... I did test the map sensor early on in this problem. Mine was testing bad, so I got a new Motocraft one. No change. I checked my wires, and double checked them. Today I checked the O2 sensor wiring and a new sensor is installed. No change.

However, I did remember a detail from when I did the work. I disconnected the catalytic converter to pull the engine up, and in the process snapped two of the three bolts holding it on. I got a nice exhaust leak right there where my sensor is. Is it at all possible that this is letting air in and giving it a false lean reading?
Wait. I have headers, and my O2 sensor may be in a different place than yours. How close is your sensor to your leak?
 


Rock Auto 5% Discount Code: 173A8B749AB83C Expires: January 1, 2020

Paulos

Active member
Joined
May 7, 2018
Messages
254
Reaction score
91
Points
28
Location
North Carolina
Vehicle Year
1987 STX
Make / Model
Ford
Engine Type
2.9 V6
Engine Size
2.9L
Transmission
Manual
2WD / 4WD
4WD
I've heard people on this forum say that an exhaust leak at the front of the cat would cause problems with the O2 sensor readings, but I never understood how. With the engine running there should always be positive pressure on the exhaust, which should prevent air from the exhaust leak getting in (that would require negative pressure). I wouldn't think it could create a venturi effect either, because of the positive pressure. But what do I know? I can't get cheap Mevotech ball joints to work right.
 

Nez'sRanger

Active member
Joined
Oct 6, 2018
Messages
160
Reaction score
43
Points
28
Location
Los Angeles, CA
Vehicle Year
1989
Make / Model
Ford
Engine Size
2.9L V6
Transmission
Manual
Wait. I have headers, and my O2 sensor may be in a different place than yours. How close is your sensor to your leak?
It's less than 2" before the leak, immediately before the cat's seam.

I've heard people on this forum say that an exhaust leak at the front of the cat would cause problems with the O2 sensor readings, but I never understood how. With the engine running there should always be positive pressure on the exhaust, which should prevent air from the exhaust leak getting in (that would require negative pressure). I wouldn't think it could create a venturi effect either, because of the positive pressure. But what do I know? I can't get cheap Mevotech ball joints to work right.
Yes, that's what I thought too, but I'm at my wit's end, so I'm starting to open to crazy sounding ideas! Haha!
 

Alaska Diesel

Member
Joined
Sep 22, 2019
Messages
35
Reaction score
2
Points
8
Location
Palmer Ak
Vehicle Year
1986, 1987
Make / Model
Ford Ranger
Engine Type
2.9 V6
Transmission
Manual
2WD / 4WD
4WD
I have a similar issue. Except I'm pretty sure my vacuum is good. And I changed my ECT temperature and swapped my IAT out. Still is hard almost impossible to keep run when cold. Have to really play with the throttle to get it to rev up. Has a smell of gas in the intake. I've also put a different map sensor on, tried a different computer. If I unplug the ECT or IAT sensors it will run good. I'm stumped on this little guy.
O2 sensor is new a couple years ago. I've only put 55 miles on it since then because the fuel pumps went out and after the fuel pumps went out I've had this issue.
 

Nez'sRanger

Active member
Joined
Oct 6, 2018
Messages
160
Reaction score
43
Points
28
Location
Los Angeles, CA
Vehicle Year
1989
Make / Model
Ford
Engine Size
2.9L V6
Transmission
Manual
I plugged my exhaust leak... No change... Except it's quieter.
I can't imagine what it could be.
 

PetroleumJunkie412

2.9 Mafia
Supporting Member
TRS 20th Anniversary
Joined
Oct 31, 2018
Messages
2,722
Reaction score
1,940
Points
113
Location
Pittsburgh, PA
Vehicle Year
1988
Make / Model
Ranger
Engine Type
2.9 V6
Transmission
Manual
2WD / 4WD
4WD
Just out of curiosity, what's the part number and make of the O2 you have in it?
 

Shran

Junk Collector
Supporting Member
Article Contributor
V8 Engine Swap
Solid Axle Swap
Joined
Mar 4, 2008
Messages
4,499
Reaction score
268
Points
83
Location
Rapid City SD
I am under the impression that since our trucks have heated O2 sensors, it does not matter much where it's located as long as it's in the exhaust stream. I can't imagine why even a large leak would affect it at all - there's still exhaust flowing over it. It would be a different situation if they were not heated and relied on catalytic converter heat to read correctly.
 

BSwift

New member
Joined
Nov 5, 2019
Messages
10
Reaction score
0
Points
1
Location
Oklahoma
Vehicle Year
1989
Make / Model
Bronco II
Engine Type
2.9 V6
Transmission
Manual
2WD / 4WD
4WD
I watched a number of U-tube videos on O2 sensors and your exhaust leak could cause the issue, plus an exhaust leak is not good and could possibly lead to carbon monoxide poisoning.
 

Nez'sRanger

Active member
Joined
Oct 6, 2018
Messages
160
Reaction score
43
Points
28
Location
Los Angeles, CA
Vehicle Year
1989
Make / Model
Ford
Engine Size
2.9L V6
Transmission
Manual
I watched a number of U-tube videos on O2 sensors and your exhaust leak could cause the issue, plus an exhaust leak is not good and could possibly lead to carbon monoxide poisoning.
Yes, I was thinking that too... However, I fixed the exhaust leak, and it didn't fix the problem. I've yet to figure out the problem.
 

PetroleumJunkie412

2.9 Mafia
Supporting Member
TRS 20th Anniversary
Joined
Oct 31, 2018
Messages
2,722
Reaction score
1,940
Points
113
Location
Pittsburgh, PA
Vehicle Year
1988
Make / Model
Ranger
Engine Type
2.9 V6
Transmission
Manual
2WD / 4WD
4WD
I may be wrong, but I think you have the wrong O2. Bosch I had was a 13942.
 

Nez'sRanger

Active member
Joined
Oct 6, 2018
Messages
160
Reaction score
43
Points
28
Location
Los Angeles, CA
Vehicle Year
1989
Make / Model
Ford
Engine Size
2.9L V6
Transmission
Manual
I may be wrong, but I think you have the wrong O2. Bosch I had was a 13942.
Yes, from what I read, the only difference between that one and the one I got is the length of the wire. I got the 19 inch wire on mine, and that one is an 11 inch.
 

PetroleumJunkie412

2.9 Mafia
Supporting Member
TRS 20th Anniversary
Joined
Oct 31, 2018
Messages
2,722
Reaction score
1,940
Points
113
Location
Pittsburgh, PA
Vehicle Year
1988
Make / Model
Ranger
Engine Type
2.9 V6
Transmission
Manual
2WD / 4WD
4WD
Yes, from what I read, the only difference between that one and the one I got is the length of the wire. I got the 19 inch wire on mine, and that one is an 11 inch.
Read that as well. I have a used 13942 if you want to give it a shot
 

alwaysFlOoReD

Forum Staff Member
Forum Moderator
TRS Banner 2012-2015
TRS 20th Anniversary
Joined
Apr 13, 2009
Messages
9,594
Reaction score
729
Points
113
Location
Red Deer, Canada
Vehicle Year
'91, '94, '80
Make / Model
Ford, GMC
Engine Size
4.0,4.0,350
Transmission
Manual
Exhaust leaks don't only let exhaust out, they also suck in outside air in between pulses. This can screw with the o2.
 

Nez'sRanger

Active member
Joined
Oct 6, 2018
Messages
160
Reaction score
43
Points
28
Location
Los Angeles, CA
Vehicle Year
1989
Make / Model
Ford
Engine Size
2.9L V6
Transmission
Manual
Read that as well. I have a used 13942 if you want to give it a shot
The first one I bought was a motorcraft with an 11 inch. I didn't know the difference existed yet, but soon found out my harness was too short to reach, so I ended up splicing longer wires in. At this point, I think I'm gonna step back and reevaluate some electrical stuff.
 


Top