check engine light
Thread Starter
|
New User
Joined: Jun 2014
Posts: 3
Likes: 0
check engine light
i hope someone can help me with this problem. i have a 1994 F250 two wheel drive with a 5.0 the check engine light keeps coming on and off after about 10-15 miles of driving when it comes on seems to run OK but as soon as the light goes out i have no throttle at all unless i mash the gas then it seems to down shift and all well until a minute later then light comes back and my mileage is getting bad on here is what i have recently done i have replaced both positive and neg cables replace the temp sensor at the t stat checked and repaired a vacuum line checked all wiring and just two days ago i change the tps sensor for the third time because all troubleshooting pointed at failure again and replace the idle air control i cannot pull up any codes either by machine or the old fashion blink code method so i am at wits end in finding the problem i don't just want to change parts as this can be costly any help is greatly appreciated Thanks in advance Ed
Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
EDIT:
Check post #4 below before reading this post.
Sounds like another bad PCM Computer.
Pull it out, open it up and check the electrolytic capacitors.
See if they are leaking or bulging. See if the acid has ate any traces.
If they are bad bridge any gaps, replace the electrolytic capacitors and clean the board.
Or take it to a radio repair shop and have them replace them.
Check post #4 below before reading this post.
Sounds like another bad PCM Computer.
Pull it out, open it up and check the electrolytic capacitors.
See if they are leaking or bulging. See if the acid has ate any traces.
If they are bad bridge any gaps, replace the electrolytic capacitors and clean the board.
Or take it to a radio repair shop and have them replace them.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,652
Likes: 79
From: Mooresville, NC
i hope someone can help me with this problem. i have a 1994 F250 two wheel drive with a 5.0 the check engine light keeps coming on and off after about 10-15 miles of driving when it comes on seems to run OK but as soon as the light goes out i have no throttle at all unless i mash the gas then it seems to down shift and all well until a minute later then light comes back and my mileage is getting bad on here is what i have recently done i have replaced both positive and neg cables replace the temp sensor at the t stat checked and repaired a vacuum line checked all wiring and just two days ago i change the tps sensor for the third time because all troubleshooting pointed at failure again and replace the idle air control i cannot pull up any codes either by machine or the old fashion blink code method so i am at wits end in finding the problem i don't just want to change parts as this can be costly any help is greatly appreciated Thanks in advance Ed
Ford changed out computers right around 1994..........is yours the 60 Pin or 104 Pin version?
Could be the computer, but there are numerous other possibilities:
- Battery, alternator, any other issue in charging circuit can introduce anomalies
- Check EEC relay for battery voltage (when on)
- Check Pin 30 on the computer (in Neutral) for either GND or SIG-RTN
- Check Pin 48 at computer harness for shorts to GND
- Check Self Test Output for shorts to GND
- Check resistance between NEG (at battery) and Pins 20, 40, and 60 on the computer harness -- 5.0 ohms or less is acceptable.
- Turn Key to ON with engine OFF and computer pulled. Measure voltage on Pins 1, 37, and 57. 10.5V or greater and all within 1.0V of one another is acceptable.
- Turn Key to ON and engine OFF with computer re-installed. Measure voltage between Pin 26 and 46. 4.0-6.0V is acceptable.
- Measure resistance between Pin 46 and Pin 40, Pin 60 at the computer harness. Less than 5.0 ohms is acceptable.
Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
When you replaced the NEG cable did reconnected it to the engine block and not the frame?
Did it have a smaller wire leaving the NEG post and going to the Body as in the photo below?
Grounding the frame is OK but not necessary unless you are pulling a trailer. But the engine block must be grounded.
The Body (not the frame) Must also be grounded as in the photo below. Note the smaller wires. The one with the white stripe is the Computer ground.
/
Did it have a smaller wire leaving the NEG post and going to the Body as in the photo below?
Grounding the frame is OK but not necessary unless you are pulling a trailer. But the engine block must be grounded.
The Body (not the frame) Must also be grounded as in the photo below. Note the smaller wires. The one with the white stripe is the Computer ground.
/
Fleet Owner
Joined: Oct 2005
Posts: 20,784
Likes: 1,751
From: Kentucky
Ford changed out computers right around 1994..........is yours the 60 Pin or 104 Pin version?
Could be the computer, but there are numerous other possibilities:
- Battery, alternator, any other issue in charging circuit can introduce anomalies
- Check EEC relay for battery voltage (when on)
- Check Pin 30 on the computer (in Neutral) for either GND or SIG-RTN
- Check Pin 48 at computer harness for shorts to GND
- Check Self Test Output for shorts to GND
- Check resistance between NEG (at battery) and Pins 20, 40, and 60 on the computer harness -- 5.0 ohms or less is acceptable.
- Turn Key to ON with engine OFF and computer pulled. Measure voltage on Pins 1, 37, and 57. 10.5V or greater and all within 1.0V of one another is acceptable.
- Turn Key to ON and engine OFF with computer re-installed. Measure voltage between Pin 26 and 46. 4.0-6.0V is acceptable.
- Measure resistance between Pin 46 and Pin 40, Pin 60 at the computer harness. Less than 5.0 ohms is acceptable.
Could be the computer, but there are numerous other possibilities:
- Battery, alternator, any other issue in charging circuit can introduce anomalies
- Check EEC relay for battery voltage (when on)
- Check Pin 30 on the computer (in Neutral) for either GND or SIG-RTN
- Check Pin 48 at computer harness for shorts to GND
- Check Self Test Output for shorts to GND
- Check resistance between NEG (at battery) and Pins 20, 40, and 60 on the computer harness -- 5.0 ohms or less is acceptable.
- Turn Key to ON with engine OFF and computer pulled. Measure voltage on Pins 1, 37, and 57. 10.5V or greater and all within 1.0V of one another is acceptable.
- Turn Key to ON and engine OFF with computer re-installed. Measure voltage between Pin 26 and 46. 4.0-6.0V is acceptable.
- Measure resistance between Pin 46 and Pin 40, Pin 60 at the computer harness. Less than 5.0 ohms is acceptable.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,652
Likes: 79
From: Mooresville, NC
Actually, 1994 was the first year of OBDII........I just worked on a 1994 Ford Mustang with OBDII...........there are millions of pre-1996 (mandatory date) cars out there with OBDII -- Fords, Chevy, GM, Toyota, Nissan, other imports.........Ford started piloting OBDII in pre-1996 trucks as well........
Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
rla2005 was speaking of trucks. The first Ford OBD-II trucks was 1996 and then only limited to the F-150, 5.8L under 8500 GVW and some California trucks. Other Ford truck did not get OBD-II until 1998.
Hang around here on the 1987-1996 forum long enough and you will learn all of this as others have.
We also work with the 1997 Ford trucks that were still OBD-I on this Forum.
Hang around here on the 1987-1996 forum long enough and you will learn all of this as others have.
We also work with the 1997 Ford trucks that were still OBD-I on this Forum.
Trending Topics
Fleet Mechanic
Joined: Feb 2007
Posts: 1,652
Likes: 79
From: Mooresville, NC
rla2005 was speaking of trucks. The first Ford OBD-II trucks was 1996 and then only limited to the F-150, 5.8L under 8500 GVW and some California trucks. Other Ford truck did not get OBD-II until 1998.
Hang around here on the 1987-1996 forum long enough and you will learn all of this as others have.
We also work with the 1997 Ford trucks that were still OBD-I on this Forum.
Hang around here on the 1987-1996 forum long enough and you will learn all of this as others have.
We also work with the 1997 Ford trucks that were still OBD-I on this Forum.
Actually, you're wrong --- I owned a 1995 F-350 PS with OBD II........not sure where you're getting the info..........
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Fleet Owner
Joined: Oct 2005
Posts: 20,784
Likes: 1,751
From: Kentucky
Actually, 1994 was the first year of OBDII........I just worked on a 1994 Ford Mustang with OBDII...........there are millions of pre-1996 (mandatory date) cars out there with OBDII -- Fords, Chevy, GM, Toyota, Nissan, other imports.........Ford started piloting OBDII in pre-1996 trucks as well........
Subford did point more details but did not specifically state gasoline powered trucks of this era. Diesels are a very different animal.
I'll admit my answer was vague since I did not specially state what my answer applied to.
Fleet Owner
Joined: Oct 2005
Posts: 20,784
Likes: 1,751
From: Kentucky
I get my information from a Ford service manual. I'll admit I'm a gas powered Ford truck guy so I do overlook the diesels which got OBD-II before the gas powered Federal emission trucks. California emissions gas trucks are a whole other ball game as well.
Fleet Owner
Joined: Aug 2005
Posts: 23,666
Likes: 301
From: Easton,Ks
The first OBD-II 7.3L was 1997, so you did not know your own trucks system.
The 1995 7.3L was said to be OBD-I by the Ford shop manuals but the plug looked like a OBDII plug. It also had a different set of DTC codes then the OBD-II systems.
Some code scanners would read the 1995 7.3L codes but not all. Ford used the New Generation Star (NGS) Scan Tool to read the codes and do the tests on this system.
The 1995 7.3L also had specific tests called Key On Engine Off (KOEO) and Key On Engine Running (KOER) Tests that the OBD-II system does not have.
The OBD-II system has the P, B, C, & U codes and the 1995 7.3L system did not have any of that.
We normally do not talk & think Diesels on this Forum as FTE has a Forum for Diesels only.
Thread
Thread Starter
Forum
Replies
Last Post
SJI2A
1987 - 1996 F150 & Larger F-Series Trucks
65
Sep 11, 2018 11:21 PM
mrb455
1987 - 1996 F150 & Larger F-Series Trucks
22
Oct 1, 2009 09:38 PM