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I have a few updates and mysteries on my 81' U.S. spec 928 that I need some guidance on.
1) The car runs now! Will idle at 950-1000 RPM all day smoothly...but as soon as you press the accel. pedal down it wants to stall and the car shakes.
2) I've done all the vacuum hoses under the spider/around the engine.
3) I took out the CE Panel and thoroughly cleaned it up, polished the grounds, and installed brand new relays and fuses.
4) I'm suspecting it's only running on the Cold Start Injector?
5) None of the main injectors are getting electrical pulse.
6) Spraying starter fluid directly down the intake while it's idling revs the engine to about 2500 rpm..so I'm assuming the timing is OK.
7) New Fuel pump and Filter and is making adequate pressure.
Does someone have an L-Jet Brain that I could use to test? Or I could send you mine and see if it works (or not) for one of you guys! Any help is very much appreciated.
I'm slightly confused on how the car is even running at this point. I hope you guys can provide some insight! Thanks so much again, I can't wait to get it on the road.
The cold start injector should be enough to keep it idling. Since it has a stable idle, try pulling one or two injector electrical connectors off and see if the idle changes. Put a noid light in those connectors, it will tell you if the injectors are getting power or not.
Huh? I thought the cold start injector would only get the engine started and keep it going for a few seconds -- not all day as OP states. No way. I can't understand how the car can idle without ANY signal to injectors.
How did you test pulse to the injectors?
I can't really offer many suggestions. In my experience, a brain problem means the car will start but only run for a few moments off the cold start valve, then die. Can be restarted several times but at some point if engine warms up it'll crank but not start anymore (cold start valve only puffs gas when cold). And also in my experience, the primary cause of brain problems is a bad ground, which is either a bad fuel injection relay or a dirty ground. Recall that the system works by supplying constant voltage to the injectors but the brain is responsible for switching them to ground to get the desired duty cycle. The injectors only inject when switched to ground.
If it idles but won't take accelerator pedal, my bet would be on a vacuum leak. I've had the exact same symptoms from a leak. What's the history on the car? If the car was running properly before, what changed? There are a bunch of usual culprits for vacuum leaks from the big O-ring at the AFM, to leaking brake booster, leaking HVAC system, etc. (though it sounds like you've been through at least some of that). Oh, and the fuel regulators are connected to vacuum and they can crumble due to age as well -- not sure if that would cause your symptoms though. How about the fuel injectors, are they known good? Is it possible that your recent work around the spider left any vacuum hoses disconnected or improperly connected?
Just some ideas. Good luck on tracing the problem. When you get these Ljet cars working though, they seem pretty bulletproof and are very smooth.
Oh and don't forget that the AFM itself can be a cause (as can dirty connections to it). I posted in a separate thread recently about moving the wiper trace in the AFM slightly to have the arm move in a fresh area on the trace. I highly recommend this to all LJet owners -- even if it's not causing an actual problem to the point of not running correctly, the car will run better guaranteed!
If you haven't already put on a new cap and rotor and then replace the plugs to make sure your ignition system is nice and fresh.
This can do wonders to fix running issues along with the fact they should be replaced at least every 60K miles due to carbon buildup in the cap and corrosion from arcing.
If your car idles nice and smoothly the computer is fine. The cold start injector only works during the first 7 seconds of starting the car and is controlled by the thermo time switch, which itself has no connection with the computer.
Now for me to ask some questions .
If you depress the pedal when the car is warm does it still want to stall?
Have you replaced the green wire running from the distributor to the fender opposite of the ignition coil?
Have the injectors ever been serviced?
Have you replaced the fuel pressure regulators and damper? ( the 2 regulators are near the back of the engine, the damper is front and center)
Also, have you replaced the fuel soft lines? They pose a fire hazard if they are original.
Here is the pinout of the L jet connector for future reference.
Huh? I thought the cold start injector would only get the engine started and keep it going for a few seconds -- not all day as OP states. No way. I can't understand how the car can idle without ANY signal to injectors.
How did you test pulse to the injectors?
I can't really offer many suggestions. In my experience, a brain problem means the car will start but only run for a few moments off the cold start valve, then die. Can be restarted several times but at some point if engine warms up it'll crank but not start anymore (cold start valve only puffs gas when cold). And also in my experience, the primary cause of brain problems is a bad ground, which is either a bad fuel injection relay or a dirty ground. Recall that the system works by supplying constant voltage to the injectors but the brain is responsible for switching them to ground to get the desired duty cycle. The injectors only inject when switched to ground.
If it idles but won't take accelerator pedal, my bet would be on a vacuum leak. I've had the exact same symptoms from a leak. What's the history on the car? If the car was running properly before, what changed? There are a bunch of usual culprits for vacuum leaks from the big O-ring at the AFM, to leaking brake booster, leaking HVAC system, etc. (though it sounds like you've been through at least some of that). Oh, and the fuel regulators are connected to vacuum and they can crumble due to age as well -- not sure if that would cause your symptoms though. How about the fuel injectors, are they known good? Is it possible that your recent work around the spider left any vacuum hoses disconnected or improperly connected?
Just some ideas. Good luck on tracing the problem. When you get these Ljet cars working though, they seem pretty bulletproof and are very smooth.
Cheers!
Rick
I had it dropped off at my usual mechanic who tested it with a noid light. I'll have to call him again and find out if he tested all 8 or just one or two. I thought it was vacuum too, now that you mention it though I haven't checked that O-Ring on the AFM. I picked up the car non-running for next to nothing and this is the first time it's actually ran in what we're guessing is 5 years or so. Where are those fuel regulators? I probably know exactly what it is just need to clarify. Are they at the end of the fuel rail? The injectors are old.. have no idea of their condition, I was planning on replacing them but since I was told they're not getting pulse I figured I would look into that first. I was pretty careful to just replace lines and not leave any loose ends but I will surely check again. I may just run down to Harbour Freight and pick up a noid light and check all 8. It also smells very very rich and it's smoking a bit (like unburnt fuel kind of smoke)
Oh and don't forget that the AFM itself can be a cause (as can dirty connections to it). I posted in a separate thread recently about moving the wiper trace in the AFM slightly to have the arm move in a fresh area on the trace. I highly recommend this to all LJet owners -- even if it's not causing an actual problem to the point of not running correctly, the car will run better guaranteed!
What is the thread called? That sounds great! I can't find it for some reason.
If you haven't already put on a new cap and rotor and then replace the plugs to make sure your ignition system is nice and fresh.
This can do wonders to fix running issues along with the fact they should be replaced at least every 60K miles due to carbon buildup in the cap and corrosion from arcing.
If your car idles nice and smoothly the computer is fine. The cold start injector only works during the first 7 seconds of starting the car and is controlled by the thermo time switch, which itself has no connection with the computer.
Now for me to ask some questions .
If you depress the pedal when the car is warm does it still want to stall?
Have you replaced the green wire running from the distributor to the fender opposite of the ignition coil?
Have the injectors ever been serviced?
Have you replaced the fuel pressure regulators and damper? ( the 2 regulators are near the back of the engine, the damper is front and center)
Also, have you replaced the fuel soft lines? They pose a fire hazard if they are original.
Here is the pinout of the L jet connector for future reference.
Yes new plugs but haven't done the rotor and cap yet.
Yes it will stall (or want to stall) regardless of what the engine temp is. My Oxygen Sensor light is on but that has nothing to do with it I'm guessing.
Yes the green wire is brand new. A rodent chewed through the old one so that was one of the first things to be replaced.
I haven't serviced the injectors yet. I have run some injector cleaner but they haven't been out of the car yet.
I haven't replaced the regulators and dampers. I'll have to look for them I didn't even try to find them under there last time. Are the regulators and dampers visible with the spider on? I'll take it off again, no problem, just wondering.
Yes, fuel soft lines are new as well.
Thanks for the picture! Would I need anything other than a standard multimeter to check the inputs on the connector?
Alex, that AFM O-ring is pretty flat. I would not be surprised if there was a big air leak at that point. Also, did you clean the ground in the engine bay, lower passenger side to engine block - both sides? It's a heavy cable and it is one that can cause issues. Ultimately, that car will need the full top end refresh - spider off, new vac lines all the way around, all new O-rings, new temp sensor, and fuel lines, new rubber boots and assorted hoses. Call Roger for the list and price quote. I do belive this car will run fine once that deferred stuff is addressed. I am thinking this is not a L brain issue; at least not yet. I agree with rjtw that this may be more likely related to the AFM, and my money would be on that o-ring.
Alex, that AFM O-ring is pretty flat. I would not be surprised if there was a big air leak at that point. Also, did you clean the ground in the engine bay, lower passenger side to engine block - both sides? It's a heavy cable and it is one that can cause issues. Ultimately, that car will need the full top end refresh - spider off, new vac lines all the way around, all new O-rings, new temp sensor, and fuel lines, new rubber boots and assorted hoses. Call Roger for the list and price quote. I do belive this car will run fine once that deferred stuff is addressed. I am thinking this is not a L brain issue; at least not yet. I agree with rjtw that this may be more likely related to the AFM, and my money would be on that o-ring.
Hi Ed! Yes I didn't even check to order that when I got all the other lines. I've done most of the things you mentioned. I haven't replaced the temp sensor however. Where is it? Would that cause some of the issue?
Temp sensor is that plug on top of the water bridge, and that won't affect this issue, but could have other impacts later. It is part of the top end refresh.
Temp sensor is that plug on top of the water bridge, and that won't affect this issue, but could have other impacts later. It is part of the top end refresh.
Ah yes I remember seeing that. The only things I've l
"Refreshed" so far are the vacuum lines and fuel lines. I should probably just get the rest out of the way and do that as well. Just trying to save a bit.
This is a good thread. Most of these others have pix, as well.
I think this is the "barn-door track cleaning" thread mentioned. Below is another AFM thread.
https://rennlist.com/forums/928-foru...esitation.html Acceleration hesitation
and rjtw's post https://rennlist.com/forums/928-foru...l#post14368216
"...if you still have issues you may want to check the pot in the AFM as Speedtoys just mentioned (yours is L-Jetronic, right?) The wiper can wear grooves in the pot over time and, if worn too much, can cause incorrect A/F mixture typically at midrange RPM and throttle but usually OK at high power (because the tracks are worn the most in the middle and less as the barn door swings to full open). I just opened mine up and reset the wiper tracks, you can find more info here, and also google youtube:" https://rennlist.com/forums/928-foru...fications.html Anyone tried these Ljet modifications?
Huh? I thought the cold start injector would only get the engine started and keep it going for a few seconds -- not all day as OP states. No way. I can't understand how the car can idle without ANY signal to injectors.
How did you test pulse to the injectors?
I can't really offer many suggestions. In my experience, a brain problem means the car will start but only run for a few moments off the cold start valve, then die. Can be restarted several times but at some point if engine warms up it'll crank but not start anymore (cold start valve only puffs gas when cold). And also in my experience, the primary cause of brain problems is a bad ground, which is either a bad fuel injection relay or a dirty ground. Recall that the system works by supplying constant voltage to the injectors but the brain is responsible for switching them to ground to get the desired duty cycle. The injectors only inject when switched to ground.
If it idles but won't take accelerator pedal, my bet would be on a vacuum leak. I've had the exact same symptoms from a leak. What's the history on the car? If the car was running properly before, what changed? There are a bunch of usual culprits for vacuum leaks from the big O-ring at the AFM, to leaking brake booster, leaking HVAC system, etc. (though it sounds like you've been through at least some of that). Oh, and the fuel regulators are connected to vacuum and they can crumble due to age as well -- not sure if that would cause your symptoms though. How about the fuel injectors, are they known good? Is it possible that your recent work around the spider left any vacuum hoses disconnected or improperly connected?
Just some ideas. Good luck on tracing the problem. When you get these Ljet cars working though, they seem pretty bulletproof and are very smooth.
Cheers!
Rick
Sorry for the typo. It was supposed to be shouldn't. the cold start injector shouldn't be able to keep the engine idling.
03-16-2018, 04:18 PM
Is my L-jet Brain dead?
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