L-jetronic Troubleshooting, Runs Rough and Runs Rich |
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L-jetronic Troubleshooting, Runs Rough and Runs Rich |
BENBRO02 |
Nov 26 2017, 05:50 PM
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#1
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Member Group: Members Posts: 483 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region |
It starts okay when cold and only has a slight miss but as it warms up it starts to miss more frequently, bucks, and if hot and idling may cut off completely. If I'm on the highway it may lose 20 mph before it starts running well enough to maintain speed or accelerate. I have recently had the following replaced:
fuel tank fuel pump fuel lines and hoses fuel sending unit vacuum hoses large and small injector seals The shop also checked the vacuum advance and cleaned the injectors. I emptied my bank account with the repairs so now it's time for me to find the problem. Any Ideas? The car has a Pertronics ignition. |
jim_hoyland |
Nov 26 2017, 06:34 PM
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#2
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Get that VIN ? Group: Members Posts: 9,323 Joined: 1-May 03 From: Sunset Beach, CA Member No.: 643 Region Association: Southern California |
I would check the FI harness and a couple of the connections 1st;
1. Is the connector going to the left side of the dual relay firmly attached ? I used to have the FPump wire back off it’s spade and cause havoc. 2. Are the wires in the resistor pack all connected, look for a loose soldered wire barely making contact 3 does your FI have electrical tape repairs ? Could be a sign someone resolved a wire or two and it’s coming loose BTW: I have a L-Jet FI Barnes listed in the classifieds Good luck on this |
BENBRO02 |
Nov 26 2017, 09:25 PM
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#3
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Member Group: Members Posts: 483 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region |
I would check the FI harness and a couple of the connections 1st; 1. Is the connector going to the left side of the dual relay firmly attached ? I used to have the FPump wire back off it’s spade and cause havoc. 2. Are the wires in the resistor pack all connected, look for a loose soldered wire barely making contact 3 does your FI have electrical tape repairs ? Could be a sign someone resolved a wire or two and it’s coming loose BTW: I have a L-Jet FI Barnes listed in the classifieds Good luck on this Thanks for the advice. I'll try those and see what happens. I'm not sure I understand exactly what your saying though. I'm technically challenged and just learning where stuff is. Is it possible some thing is plugged in wrong? I did go check out your wiring harness and thought to myself that is was expensive until I saw a new one from Bowlsby is $752 plus a core charge. Now your used one in good condition seems inexpensive. |
Cupomeat |
Nov 26 2017, 09:39 PM
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#4
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missing my NY 914 in VA Group: Members Posts: 1,336 Joined: 26-November 07 From: Oakton VA Member No.: 8,376 Region Association: MidAtlantic Region |
I'd do whatever you can to make sure there is no vacuum leaks. Places I thought I had fixed before were the Valve cover gaskets (Sometimes the top of the gasket sags to allow a leak), oil filler cap gaskets AND the gasket between the oil air separator and the case. Try smoke or just using starter spray while running. Looks for something that may move when running.
Now, since you are saying there is intermittency, I'd agree with Jim and look at wiring as well. Good luck! |
BENBRO02 |
Nov 26 2017, 10:15 PM
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#5
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Member Group: Members Posts: 483 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region |
I'd do whatever you can to make sure there is no vacuum leaks. Places I thought I had fixed before were the Valve cover gaskets (Sometimes the top of the gasket sags to allow a leak), oil filler cap gaskets AND the gasket between the oil air separator and the case. Try smoke or just using starter spray while running. Looks for something that may move when running. Now, since you are saying there is intermittency, I'd agree with Jim and look at wiring as well. Good luck! Where is the oil air separator located? Thanks |
jim_hoyland |
Nov 26 2017, 10:22 PM
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#6
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Get that VIN ? Group: Members Posts: 9,323 Joined: 1-May 03 From: Sunset Beach, CA Member No.: 643 Region Association: Southern California |
Are you familiar with the dual relay and resistor pack ?
The dual relay is on the passenger side and has two connectors from the FI harness. The relays seldom go bad, but a loose connection at the base should be checked out The resistor pack is usually located near the base of the battery, it’s an aluminum shell with 4 ceramic resistors. The FI harness plugs into the resistor pack; check that connection, then verify each of the ceramic resistors has a wire soldered firmly. I mention these two; others will chime in with more things to check out. |
BENBRO02 |
Nov 26 2017, 10:30 PM
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#7
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Member Group: Members Posts: 483 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region |
I would check the FI harness and a couple of the connections 1st; 1. Is the connector going to the left side of the dual relay firmly attached ? I used to have the FPump wire back off it’s spade and cause havoc. 2. Are the wires in the resistor pack all connected, look for a loose soldered wire barely making contact 3 does your FI have electrical tape repairs ? Could be a sign someone resolved a wire or two and it’s coming loose BTW: I have a L-Jet FI Barnes listed in the classifieds Good luck on this I just drove the car around the block (about 5 miles) and although it is missing I never felt like I was in danger of being stranded. It's cold out so I would say it definitely runs better when it's cold out. I also looked in the engine compartment and inspected the wiring which in my opinion looks pretty good. |
BENBRO02 |
Nov 26 2017, 10:37 PM
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#8
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Member Group: Members Posts: 483 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region |
Are you familiar with the dual relay and resistor pack ? The dual relay is on the passenger side and has two connectors from the FI harness. The relays seldom go bad, but a loose connection at the base should be checked out The resistor pack is usually located near the base of the battery, it’s an aluminum shell with 4 ceramic resistors. The FI harness plugs into the resistor pack; check that connection, then verify each of the ceramic resistors has a wire soldered firmly. I mention these two; others will chime in with more things to check out. This helps a lot. I had no idea where these things were. Thanks |
djway |
Nov 27 2017, 12:16 AM
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#9
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Senior Member Group: Members Posts: 787 Joined: 16-October 15 From: Riverside Member No.: 19,266 Region Association: Southern California |
First since you are challenged, as we all were and are to some extent, find every L jet manual out there, download, print and read. Over and Over and Over. I had never worked on FI before and I discovered bad wires, multi vacuum leaks, a bad potentiomoter board, weak CHT sender, air density sensor was corroded and the flap spring had been moved I assume to adjust for all the air leaks. It started as the motor cutting out every so often and belching smoke. Each time I found a problem and fixed it the car ran worse until I found all the problems.
I think I started with checking continuity on all FI related wires. Then I went to vacuum leaks and found a torn plenum and a torn tube end. I did a leak test of the injectors. Checked the AFM board to adjust the wiper but it had cracks so I replaced that. Checked the cold start valve for proper operation. Checked and cleaned the full throttle position mechanism. I then checked the resistance of the CHT and it was not in spec and they were hard to find before 914 Rubber started selling them. I then checked the AFM air density sensor and found the resistance was way off so I opened it up and cleaned the contact and bingo. After that I took an AF Meter and made an exhaust extension to hold the O2 bung and jumped on the freeway to find the proper stoichiometery for the mixture. Kept pulling off the freeway and moving the spring until I got it right at 3000 rpm. She now runs like a champ after barely limping home the day of purchase. I knew NOTHING when I started. The L Jet service manuals have a check list of what to do. Start at the beginning and methodically work your way through one step at a time. Don't skip steps. If you are satisfied after completing each individual step the last thing would be the brain and I did not look into testing that. You can do it. Read, learn, go slowly, methodically and you can get there. |
rhodyguy |
Nov 27 2017, 08:56 AM
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#10
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Chimp Sanctuary NW. Check it out. Group: Members Posts: 22,097 Joined: 2-March 03 From: Orion's Bell. The BELL! Member No.: 378 Region Association: Galt's Gulch |
When warm, do you have a normal idle speed or a struggle to keep the engine idling at all?
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Dave_Darling |
Nov 27 2017, 10:14 AM
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#11
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914 Idiot Group: Members Posts: 14,991 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
What does the tach do when the engine starts missing? If the needle jumps all over, you definitely have an ignition system problem. (A lack of jumping around doesn't rule out ignition, so this is can only confirm one possibility but it will not deny any.)
Intermittent problems are usually electrical. If it runs fine for a while then runs crappy, there's a very good chance that the problem is an electrical connection.... somewhere. If it runs crappy all the time, it could be a lot of different things. Do you have an IR thermometer? If so, run the motor for a while and then zap each exhaust tube near the head. If you find one is rather cooler than the others, that says you have one cylinder that isn't firing or is intermittently firing. If the pipe is dead cold, you have a "dead hole" and you can start checking stuff for that one cylinder. You may be able to tell large variations in temperature by holding your hand NEAR each pipe in turn, but DO NOT TOUCH THEM unless you enjoy second-degree burns. Good luck! --DD |
timothy_nd28 |
Nov 27 2017, 01:17 PM
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#12
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Advanced Member Group: Members Posts: 2,299 Joined: 25-September 07 From: IN Member No.: 8,154 Region Association: Upper MidWest |
I hate intermittent issues, but it sounds like you can duplicate the issue easily once the engine has warmed up.
If I were in your shoes, I would warm the engine up till it starts to miss. At this point, I would then attach a timing light to any spark plug wire and stare at the strobing light as your engine is stumbling. Then I would move the timing light to the other three remaining plug wires. You should see a consistent strobe pattern of light, any pauses in this pattern would indicate a ignition problem vs fuel. I think this would be the easiest to differentiate between spark and fuel, which should be the first step in any diagnosis. |
JeffBowlsby |
Nov 27 2017, 01:50 PM
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#13
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914 Wiring Harnesses Group: Members Posts: 8,537 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None |
Links to 4 different L-Jet diagnostic manuals can be found here:
http://bowlsby.net/914/Classic/TechNotebook.htm |
Cupomeat |
Nov 27 2017, 02:30 PM
Post
#14
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missing my NY 914 in VA Group: Members Posts: 1,336 Joined: 26-November 07 From: Oakton VA Member No.: 8,376 Region Association: MidAtlantic Region |
I'd do whatever you can to make sure there is no vacuum leaks. Places I thought I had fixed before were the Valve cover gaskets (Sometimes the top of the gasket sags to allow a leak), oil filler cap gaskets AND the gasket between the oil air separator and the case. Try smoke or just using starter spray while running. Looks for something that may move when running. Now, since you are saying there is intermittency, I'd agree with Jim and look at wiring as well. Good luck! Where is the oil air separator located? Thanks Sorry for the delay, it is the stack below the oil fill. There is a cork gasket between it and the block that can sometimes leak air. Good luck! |
BENBRO02 |
Nov 27 2017, 05:32 PM
Post
#15
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Member Group: Members Posts: 483 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region |
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BENBRO02 |
Nov 27 2017, 05:35 PM
Post
#16
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Member Group: Members Posts: 483 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region |
Links to 4 different L-Jet diagnostic manuals can be found here: http://bowlsby.net/914/Classic/TechNotebook.htm Thanks, I had already found one and the others will come in handy. I can't wait to become an L-jetronic expert. |
BENBRO02 |
Nov 27 2017, 05:43 PM
Post
#17
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Member Group: Members Posts: 483 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region |
I hate intermittent issues, but it sounds like you can duplicate the issue easily once the engine has warmed up. If I were in your shoes, I would warm the engine up till it starts to miss. At this point, I would then attach a timing light to any spark plug wire and stare at the strobing light as your engine is stumbling. Then I would move the timing light to the other three remaining plug wires. You should see a consistent strobe pattern of light, any pauses in this pattern would indicate a ignition problem vs fuel. I think this would be the easiest to differentiate between spark and fuel, which should be the first step in any diagnosis. Excellent idea, thanks |
BENBRO02 |
Nov 27 2017, 05:46 PM
Post
#18
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Member Group: Members Posts: 483 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region |
What does the tach do when the engine starts missing? If the needle jumps all over, you definitely have an ignition system problem. (A lack of jumping around doesn't rule out ignition, so this is can only confirm one possibility but it will not deny any.) Intermittent problems are usually electrical. If it runs fine for a while then runs crappy, there's a very good chance that the problem is an electrical connection.... somewhere. If it runs crappy all the time, it could be a lot of different things. Do you have an IR thermometer? If so, run the motor for a while and then zap each exhaust tube near the head. If you find one is rather cooler than the others, that says you have one cylinder that isn't firing or is intermittently firing. If the pipe is dead cold, you have a "dead hole" and you can start checking stuff for that one cylinder. You may be able to tell large variations in temperature by holding your hand NEAR each pipe in turn, but DO NOT TOUCH THEM unless you enjoy second-degree burns. Good luck! --DD Thanks it's great hearing all these ideas. |
BENBRO02 |
Nov 27 2017, 05:47 PM
Post
#19
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Member Group: Members Posts: 483 Joined: 6-March 15 From: Nokesville, Virginia Member No.: 18,493 Region Association: MidAtlantic Region |
First since you are challenged, as we all were and are to some extent, find every L jet manual out there, download, print and read. Over and Over and Over. I had never worked on FI before and I discovered bad wires, multi vacuum leaks, a bad potentiomoter board, weak CHT sender, air density sensor was corroded and the flap spring had been moved I assume to adjust for all the air leaks. It started as the motor cutting out every so often and belching smoke. Each time I found a problem and fixed it the car ran worse until I found all the problems. I think I started with checking continuity on all FI related wires. Then I went to vacuum leaks and found a torn plenum and a torn tube end. I did a leak test of the injectors. Checked the AFM board to adjust the wiper but it had cracks so I replaced that. Checked the cold start valve for proper operation. Checked and cleaned the full throttle position mechanism. I then checked the resistance of the CHT and it was not in spec and they were hard to find before 914 Rubber started selling them. I then checked the AFM air density sensor and found the resistance was way off so I opened it up and cleaned the contact and bingo. After that I took an AF Meter and made an exhaust extension to hold the O2 bung and jumped on the freeway to find the proper stoichiometery for the mixture. Kept pulling off the freeway and moving the spring until I got it right at 3000 rpm. She now runs like a champ after barely limping home the day of purchase. I knew NOTHING when I started. The L Jet service manuals have a check list of what to do. Start at the beginning and methodically work your way through one step at a time. Don't skip steps. If you are satisfied after completing each individual step the last thing would be the brain and I did not look into testing that. You can do it. Read, learn, go slowly, methodically and you can get there. Wow, very detailed and helpful. Thanks for taking the time to help. |
Mueller |
Nov 27 2017, 06:10 PM
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#20
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None |
On my last 1.8 I made plugs that go into the boot to help eliminate vac. leaks.
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