L Jetronic questions
01-22-2004, 08:05 PM
#1
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L Jetronic questions
Having earned my cub scout merit badges on electrical and suspension, it is now time to tweak the fuel injection. The idle has been wobbling around a bit, so I pulled out Volume 1-a and popped the air filter and started poking around and testing a few things.
The first thing I noticed was that the short rubber return hoses for the fuel injection system were cracked and ratty looking. I swapped those out which requires small hands and an absolute belief that they aren't under pressure as you cut them off!
I also found that a clamp was missing on one of the vacuum hoses that plugs into the middle of the AFM. It looked loose enough that it may have been leaking a bit. I also noticed about an ounce of oil on top of the engine that was slowly turning to asphalt. I have no idea where that came from, as I didn't see it 6 months ago when I changed the vacuum lines. All the valve covers look fine and there is no obvious oil on any of the hoses.
I cleaned out the mystery oil sludge and I then tested a few electrical things. The first was Temperature sensor 2, which ohmed out correctly both hot and cold.
The second was the temperature time switch. This was not right on spec.
Cold measured (ohms) spec
G to gnd 2 0 ok
W to gnd 2 0 ok
W to G 2 25-40 Low
Hot measured (ohms) spec
G to gnd 120 100-160 ok
W to gnd 66 100-160 Low
W to G 60 50-80 ok
So it looks like I need a new TTS. There's $54. Why did I start testing stuff again??
On to the auxiliary air meter. This tested out at 16 ohms vs a spec of 40 to 75. These are more expensive.
What's the consensus? Do I need a new AAM too or is this "close enough"? Anybody ever torn one of these apart? Are there other test procedures for these things?
TIA
The first thing I noticed was that the short rubber return hoses for the fuel injection system were cracked and ratty looking. I swapped those out which requires small hands and an absolute belief that they aren't under pressure as you cut them off!
I also found that a clamp was missing on one of the vacuum hoses that plugs into the middle of the AFM. It looked loose enough that it may have been leaking a bit. I also noticed about an ounce of oil on top of the engine that was slowly turning to asphalt. I have no idea where that came from, as I didn't see it 6 months ago when I changed the vacuum lines. All the valve covers look fine and there is no obvious oil on any of the hoses.
I cleaned out the mystery oil sludge and I then tested a few electrical things. The first was Temperature sensor 2, which ohmed out correctly both hot and cold.
The second was the temperature time switch. This was not right on spec.
Cold measured (ohms) spec
G to gnd 2 0 ok
W to gnd 2 0 ok
W to G 2 25-40 Low
Hot measured (ohms) spec
G to gnd 120 100-160 ok
W to gnd 66 100-160 Low
W to G 60 50-80 ok
So it looks like I need a new TTS. There's $54. Why did I start testing stuff again??
On to the auxiliary air meter. This tested out at 16 ohms vs a spec of 40 to 75. These are more expensive.
What's the consensus? Do I need a new AAM too or is this "close enough"? Anybody ever torn one of these apart? Are there other test procedures for these things?
TIA
01-22-2004, 08:50 PM
#2
Marc,
Before replacing either I would perform additional checks. Use a test light and see if the cold start injector shuts off after 2 to 12 seconds (temp dependant). If it does, leave the thermotime switch alone. If your idle at cold and warm temps is within spec, don't replace the auxillary air valve. BTW, neither of these will normally cause a flucuating idle rpm.
Dennis
Before replacing either I would perform additional checks. Use a test light and see if the cold start injector shuts off after 2 to 12 seconds (temp dependant). If it does, leave the thermotime switch alone. If your idle at cold and warm temps is within spec, don't replace the auxillary air valve. BTW, neither of these will normally cause a flucuating idle rpm.
Dennis
01-22-2004, 09:20 PM
#3
I had an issue with hunting idle and narrowed it to a vacuum leak in the cruise control baffles. Since the electronic control doesn't work, I capped off the vacuum line to the baffles and it idles much better.
BTW, ignition timing can affect idle stability as well. Make sure you have it set right before dropping $$ on parts.
BTW, ignition timing can affect idle stability as well. Make sure you have it set right before dropping $$ on parts.
01-22-2004, 09:29 PM
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Thanks for the tips. My cruise is working fine and holds a vacuum well. I will definitely have a look at the cold start injector.
My idle is sometimes within spec and seems to change from around 800 to about 1200 depending on the stars. I really have two different problems - one that causes the idle to wander around - which I suspect is a vacuum leak, and some other control issue that causes it to oscillate between 300 and 1800 when the engine was partly warmed up. This second problem seems to occur if I park the car when it has not warmed up all the way, and then go back out and restart it.
These were the first tests I have done, but my plan is to continue systematically through the system until I find and punish the guilty parts!
My idle is sometimes within spec and seems to change from around 800 to about 1200 depending on the stars. I really have two different problems - one that causes the idle to wander around - which I suspect is a vacuum leak, and some other control issue that causes it to oscillate between 300 and 1800 when the engine was partly warmed up. This second problem seems to occur if I park the car when it has not warmed up all the way, and then go back out and restart it.
These were the first tests I have done, but my plan is to continue systematically through the system until I find and punish the guilty parts!
01-22-2004, 10:30 PM
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To test the cold start injector switch (temperature time switch), just unplug it when off. If the car becomes difficult to start, then it's working. If you unplug it when the car is warm, and it runs better, it might be bad.
Might be an injector issue.
A rythmic idle up and down might be a tired vacuum limiter (UFO shaped thing on the side of the throttle body.) It can be replaced with a 5/8" and 3/4" rubber heater hose blockoff plugs with no ill effect.
Might be an injector issue.
A rythmic idle up and down might be a tired vacuum limiter (UFO shaped thing on the side of the throttle body.) It can be replaced with a 5/8" and 3/4" rubber heater hose blockoff plugs with no ill effect.
01-23-2004, 12:55 AM
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Scott,
If you're asking about the vacuum limiter, it's on the right side of the throttle body.
I don't have a picture of it, but this is what it looks like without it:
If you're asking about the vacuum limiter, it's on the right side of the throttle body.
I don't have a picture of it, but this is what it looks like without it:
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01-23-2004, 01:22 AM
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Thanks Ken,
It looks like they also call it a "decel valve" in the WSM. They have a procedure on 24-19 that I'll try. The test is to apply vacuum and at some point the valve will open and the idle speed will rise.
It looks like they also call it a "decel valve" in the WSM. They have a procedure on 24-19 that I'll try. The test is to apply vacuum and at some point the valve will open and the idle speed will rise.
01-23-2004, 01:56 AM
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I've been looking through the archives, and the Vacuum limiter (aka Decel valve) could be an issue. It is supposed to crank a bit of extra air in when you decelerate to keep the mixure correct. Currently if I come off the throttle all the way my tach bounces off zero before it stabilizes.
01-23-2004, 07:53 AM
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Marc,
I had an "Eureka" moment when I read your last post...
["tach bounces off zero"... following a complete throttle lift.]
My '80 5-sp has done this before, and remains on the hairy edge of a repeat performance. The issue has nothing to do with vacuum, but is the delicate adjustment of the off-throttle micro switch.
This lower switch (of two) on the throttle shaft controls a fuel cut off:If it isn't timed to close with throttle lift off at low speed - go for the brakes as eng braking is lost. The converse, which could be your case (and was mine) is that when the throttle shaft cam closes the 'micro' prematurely, the eng. dies momentarily.
You can hear the micros 'click': this one should open within a few thou of the throttle coming off idle- as detailed in the FSM's. After reading the manuel in all it's glory, go and set it by ear! (two screws and the world's shortest screwdriver)
Auto's are not as sensitive to this setting as 5-sp's. The upper switch positioning is complicated to read about, but is in reality not nearly as position sensitive - it controls wide open throttle enrichment.
I had an "Eureka" moment when I read your last post...
["tach bounces off zero"... following a complete throttle lift.]
My '80 5-sp has done this before, and remains on the hairy edge of a repeat performance. The issue has nothing to do with vacuum, but is the delicate adjustment of the off-throttle micro switch.
This lower switch (of two) on the throttle shaft controls a fuel cut off:If it isn't timed to close with throttle lift off at low speed - go for the brakes as eng braking is lost. The converse, which could be your case (and was mine) is that when the throttle shaft cam closes the 'micro' prematurely, the eng. dies momentarily.
You can hear the micros 'click': this one should open within a few thou of the throttle coming off idle- as detailed in the FSM's. After reading the manuel in all it's glory, go and set it by ear! (two screws and the world's shortest screwdriver)
Auto's are not as sensitive to this setting as 5-sp's. The upper switch positioning is complicated to read about, but is in reality not nearly as position sensitive - it controls wide open throttle enrichment.
01-23-2004, 12:47 PM
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Take all the ohm measurements with a grain of salt, especially when it comes to fuel injection components. I have replaced many suspected bad components due to ohm readings not being in the range specified within the manuals only to have the new part read identically. This does not apply to continuity to ground measurements. The temp time switch and cold start injector can be checked at the jump start terminal by taking a small jumper wire and applying power to the appropriate pin on terminal 14 behind the jump start terminal. If everything is good, you can hear the cold start injector click when power is applied (engine cold)
01-23-2004, 01:27 PM
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Garth - You may have nailed the surging. I replaced that switch a few months back and that is indeed when it started. I had no idea it was that sensitive. I will readjust it.
Bruce - Thanks that is good to know, and good trick on the cold start injector.
After re-reading my Bosch books and thinking more on the behavior of the engine, I think the cold start and auxiliary air regulator are probably fine. I'd have other symptoms if they were misbehaving. I am going to move them down the troubleshooting list.
Today's tasks in the quest of perfect L-Jetronic performance:
1) Re-adjust the microswitch (surging)
2) Test the decel valve (tach goes to zero when shifting)
3) Check out the O2 sensor readings (wandering idle)
Thanks for all the info!
Bruce - Thanks that is good to know, and good trick on the cold start injector.
After re-reading my Bosch books and thinking more on the behavior of the engine, I think the cold start and auxiliary air regulator are probably fine. I'd have other symptoms if they were misbehaving. I am going to move them down the troubleshooting list.
Today's tasks in the quest of perfect L-Jetronic performance:
1) Re-adjust the microswitch (surging)
2) Test the decel valve (tach goes to zero when shifting)
3) Check out the O2 sensor readings (wandering idle)
Thanks for all the info!
01-23-2004, 04:08 PM
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The plot thickens.
I readjusted the micro switch so that it is triggered within a few mils of throttle off. I went to fire up the car and it cranked but wouldn't fire. WTF. So I opened up the hood and checked all the stuff I had fiddled with sure enough I had left the connector off of the temperature time switch. Good thing I don't work on 747s.
Plugged that back in and it started to fire and then just cranked. Probably a fuel problem with the cold start injector adding just enough fuel to get it to run a cycle or two. Remembering that I had replaced the fuel return lines I jumpered the pump and let it run for a bit to clear out any air. Put the relay back in and it fired right up. Whew.
Went out for a test drive. The behavior had changed a bit. The tach didn't zero out between shifts, it drifted down slowly. Idle seemed more stable but I wouldn't know until it warmed up. Once warm, the bounce to zero between shifts returned. Hmm.
Brought it back into the driveway, popped the hood and checked that the idle microswitch was adjusted correctly. It hadn't moved and switched properly. I checked that it was actually doing something by bringing the revs up a bit and manually switching it.
I then pulled out the might vac and tested the decel valve. The WSM claims that if you add vacuum, the idle should rise. This indeed happened after I added a number of pumps, however then it went into the idle oscillation that I had seen before. There is one smoking gun!
Next we are going to play with the butane torch and look for vacuum leaks. I think at this point I will replace the decel valve and see what that does before I do any further work.
Thanks for all the advice!
I readjusted the micro switch so that it is triggered within a few mils of throttle off. I went to fire up the car and it cranked but wouldn't fire. WTF. So I opened up the hood and checked all the stuff I had fiddled with sure enough I had left the connector off of the temperature time switch. Good thing I don't work on 747s.
Plugged that back in and it started to fire and then just cranked. Probably a fuel problem with the cold start injector adding just enough fuel to get it to run a cycle or two. Remembering that I had replaced the fuel return lines I jumpered the pump and let it run for a bit to clear out any air. Put the relay back in and it fired right up. Whew.
Went out for a test drive. The behavior had changed a bit. The tach didn't zero out between shifts, it drifted down slowly. Idle seemed more stable but I wouldn't know until it warmed up. Once warm, the bounce to zero between shifts returned. Hmm.
Brought it back into the driveway, popped the hood and checked that the idle microswitch was adjusted correctly. It hadn't moved and switched properly. I checked that it was actually doing something by bringing the revs up a bit and manually switching it.
I then pulled out the might vac and tested the decel valve. The WSM claims that if you add vacuum, the idle should rise. This indeed happened after I added a number of pumps, however then it went into the idle oscillation that I had seen before. There is one smoking gun!
Next we are going to play with the butane torch and look for vacuum leaks. I think at this point I will replace the decel valve and see what that does before I do any further work.
Thanks for all the advice!
01-23-2004, 04:36 PM
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Marc,
Replace the valve with plugs... Porsche did on the later L-Jet cars.
As you've probably read, all it does is burp a little air when you let off the throttle sharply, in an attempt to burn any gas that has been injected and not burned.
I doubt if it would show on an emissions test with it missing.
It's one less thing to go wrong, and it's removal makes reaching under the plenum easier.
Replace the valve with plugs... Porsche did on the later L-Jet cars.
As you've probably read, all it does is burp a little air when you let off the throttle sharply, in an attempt to burn any gas that has been injected and not burned.
I doubt if it would show on an emissions test with it missing.
It's one less thing to go wrong, and it's removal makes reaching under the plenum easier.
01-23-2004, 05:54 PM
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Ken,
I'll give it try. It is certainly not helping anything. I did find that the seal around the base of the AFM was leaking so I have another one of those on order, and verified all other vacuum integrity and connections today. I still need to get to the O2 sensor.
I'll give it try. It is certainly not helping anything. I did find that the seal around the base of the AFM was leaking so I have another one of those on order, and verified all other vacuum integrity and connections today. I still need to get to the O2 sensor.