B21ft no-start

adamdrives said:

Thanks, that?s useful info, probably would have taken me a while to dig that out of the free books. I have a new enrichment switch that?s going to go in. I?ve never checked dwell before but there is an old snap on dwell meter at the shop so I?ll have to learn how to use that.

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Remember it's going to read 43ish mid swing because it's not a V8.

So some issues trying to check dwell. I got a new timing light that can also measure dwell. When I connect to the red test lead, I get a very intermittent reading. Sometimes it will read steady for a few seconds, then nothing. When I connect to the neg side of the coil (per timing light manual) I get around 60 at idle. Is that a valid way to check? The switch is new, but I'd still like to learn how to check properly. Possibly bad wiring? I haven't looked at a wiring diagram yet for that test lead.

Redwood Chair said:

Remember it's going to read 43ish mid swing because it's not a V8.

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It has a setting for multiple cylinders so I can choose 4

Choose 4 cylinder and you use the red test lead. The coil connection is for when you use points. The dwell you are checking is the the dwell or duty cycle of the lambda controller which is unrelated to the coil. It is related to the o2 sensor and if the sensor is of unknown life it may be bad. The o2 is hidden under the exhaust manifold behind the turbo. They wanted it to stay good and hot.

Connect up the dwell meter and start the engine cold. You should see 60 degrees for about thirty seconds. Then it should go down to about 50 degrees for another thirty seconds or so. After that the lambda controller will start checking the sensor for output. It actually takes about 15 minutes for the sensor to give valid readings. At around that time you should see it start swinging but centered around 43 degrees like RWC mentions. If it isn't doing that. Turn off the engine. Then disconnect the sensor at the large green wire near the firewall. Start up the engine. You should see a steady 45 degrees. If you don't then you need to troubleshoot the lambda controller and it's input signals.

If you do see the steady 45 degrees. Then you probably have a bad o2 sensor. You can connect a voltmeter to the black sensor wire and see if it is oscillating centered around .5 volts. If it is steady or stuck at one reading. I'd replace the sensor. Soak it down for a couple of days before you try to remove the sensor. Use a good penetrating oil. Since this is a car you have resurrected it's probably a good idea just to replace the sensor for good measure. If you do replace the sensor. You need an offset socket so you can get to it. Something from Schley tools or the genuine volvo tool work well.

If the sensor tests good but your dwell reading from the computer is not centered around 43. You can adjust the mixture with a 3mm allen wrench while idling hot. Be sure to have fresh oil and a clean air filter for this adjustment. There is a good writeup on this procedure in the Bentley manual.

Have at it!

Sounds like I need to trouble shoot the lambda controller. Is that the same as the idle controller? (Small black box under LH computer)

No matter what I do, I’m not getting a signal from the red test lead. Sometimes it will read for a moment when I make the connection, but nothing more than that.

The oxygen sensor is a new (old stock) genuine sensor, but it had probably been sitting around since the 80s. I haven’t back probed it to see if it’s giving and signal when the engine is hot, which I will do tomorrow.

So to clarify, the red test lead checks the duty cycle of the lambda (oxygen) sensor. What confuses me is that if it’s a one wire sensor, how does the ecu read it? Is it a passive sensor that doesn’t need power? Same question for the enrichment valve. When I back prove pin 7 I see battery voltage with the car running. I assume when the valve gets more then 2.9 psi it closes, grounding to chassis. Since it’s also a one wire sensor, getting voltage from the ecu, how does it communicate back to the ecu? It must be an input sensor, but I don’t understand how it sends a message if it’s only getting power. This may not be relevant to troubleshooting but it’s been bothering me that I don’t understand.

Thanks for the detailed responses, getting exited about driving this car with full power. As it is it’s so much better than when I first drove it with bad injectors, but it still feels chocked when I get into boost.

I wouldn't be too quick to blame the car. The dwell meters used back when your manuals were written were very simple, and not easily fooled. The 45 degree dwell represents a signal that is high 50% of the time, 45 out of 90, what is called a square wave with equal duty cycle. See if your DMM reads "duty cycle" and gives you a steady reading compared to your timing light, which may not. Or, perhaps you can find someone who will lend you one of the old tach/dwell meters used to set ignition points. At least get another meter on it before going after the lambda controller (which is separate from the idle controller). You can backprobe the oxygen sensor, but be aware it doesn't start telling you the truth until it is warm.

Regarding the one-wire sensors, they generate voltage referred to ground (oxygen) or offer resistance referred to ground (temp) so in effect they are really two wire. The three and four wire oxygen sensors have extra leads to run the heaters in them when the sensors are located some distance from the fire.

Ok, so dwell is a calculation based on duty cycle, which is measured on a scale with a max of 90 (units?) Thats helpful to know.

I've tried my DMM, the timing light, and an old snap-on dwell meter (that had some bad solder joints inside I repaired just to be sure) and had the same results each time: dwell readings appear when testing at the neg side of the coil, and not at the red test lead by the little black power distribution box.

In that case, is the enrichment valve offering resistance to ground? It seems like an open or closed switch, with no load, so I'm confused. I'm still not sure how it can send any meaningful information to the ecm as a powered, one wire sensor. I also see there are two wires going to on the harness side: one green and one grey (I believe, i'm slightly colorblind). On the wiring diagram pin 7 from the ecm branches off into two parallel circuits, one to the temp sensor, one to the enrichment valve. Are they actually in series?

adamdrives said:

Ok, so dwell is a calculation based on duty cycle, which is measured on a scale with a max of 90 (units?) Thats helpful to know.

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Dwell really just references the ignition. The recommendation to use a "dwell meter" is really made to measure duty cycle to mechanics in the 80's who had dwell meters. Dwell is number of degrees in the rotation of the distributor that ignition points are closed, charging the coil. So with a 4-cyl, there are 4 sequences of 90 degrees.

What you're measuring when you connect to the test point is the duty cycle of the frequency valve. If the frequency valve stops buzzing, I guess your "dwell" measurement will bottom out. The mid point of the valve's operation would be when it is passing fuel 50% of the time, corresponding to 45 degrees on the dwell meter.

adamdrives said:

I've tried my DMM, the timing light, and an old snap-on dwell meter (that had some bad solder joints inside I repaired just to be sure) and had the same results each time: dwell readings appear when testing at the neg side of the coil, and not at the red test lead by the little black power distribution box.

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That sounds like good evidence the frequency valve may not be buzzing?

adamdrives said:

In that case, is the enrichment valve offering resistance to ground? It seems like an open or closed switch, with no load, so I'm confused. I'm still not sure how it can send any meaningful information to the ecm as a powered, one wire sensor. I also see there are two wires going to on the harness side: one green and one grey (I believe, i'm slightly colorblind). On the wiring diagram pin 7 from the ecm branches off into two parallel circuits, one to the temp sensor, one to the enrichment valve. Are they actually in series?

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Each sensor references ground, and as far as where the power comes from to read the sensor, only the lambda sond makes its own power. Nevertheless, with it disconnected you can measure a half-volt at its ECU connector, due to a bias placed on it by the control unit. When the sensor warms up, its output overcomes that bias and is measured in the control unit.

The other sensor are checked the same way your ohmmeter checks resistance, by passing a known current and measuring the resulting voltage. Here's my attempt to explain the controller's operation. http://cleanflametrap.com/kjetControlller.htm

The O2 sensor's performance can be checked a couple of ways-once warmed up, pull a vacuum line and see how the voltage reacts.Then add a little propane to the vacuum port and check that reaction. This gives full lean/rich conditions and a bad sensor won't respond appropriately. But before it goes completely kaput, it will get sluggish.This can be seen with an oscilloscope on the output wire. A sluggish sensor will have fewer crosscurrent voltage swings than it should. Crosscurrent specs come from the sensor's manufacturer. Some sensors can be revived by heating them with a torch to remove deposits. Most mechanics never check these due to time($$) constraints and just replace the sensor.

From what I am reading. I would suggest as Art also suggests. If you don't hear the frequency valve buzzing. It's time to make sure the lambda controller is getting powered up. The lambda controller gets it's power up signal from the small square relay on the left inner fender. It is called the lambda relay. It turns on the lambda controller, and provides power to other things like the frequency valve and control pressure regulator.

Now the lambda relay gets turned on by the fuel pump relay. Terminal 87b if I recall correctly. I have had fuel pump relays that failed to output to the lambda relay and your controller never powers up. Also the lambda relay itself can fail. So listen for the buzzing and if you don't hear it. Check the lambda relay which if it's now powering up then move to the fuel pump relay.

98% + of the time the 3mm adjustment on the fuel distributor is correct and changing it to account for a problem you haven't found yet is a temporary measure at best.

Redwood Chair said:

98% + of the time the 3mm adjustment on the fuel distributor is correct and changing it to account for a problem you haven't found yet is a temporary measure at best.

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^^^
This is very true! Words of wisdom. Don't change it till you know the other stuff is working properly.

More K-jet Black Magic.

dl242gt said:

^^^
This is very true! Words of wisdom. Don't change it till you know the other stuff is working properly.

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Right down to the brake booster holding vacuume for several hours.

Also the tiniest amount you turn it makes a big difference, plus the allen key's pressure on the plate counts, so you'll need to remove it each time you adjust & re-test.

So, to clarify, the red test lead is an output from the ecm of the frequency valve duty cycle? Is the "lambda computer" the LH computer? If not, where is it?

The lambda relay (red wire in, two grey out?) is getting and passing power. Its a new relay. I haven't checked the ecm to see if its getting power.

I can hear the valve buzzing (I think, unless the meter flap makes some noise too) and when I back probe the connector terminals I see battery voltage at one and voltage oscillating around 14 at the other.

I've verified the oxygen sensor works beyond a shadow of a doubt. I can see oscillation at idle, I get a response from creating a vac leak, and it will peg rich after settling to idle after I snap the throttle. After idling for 15 minutes hot, the reading will stabilize around 0.750.

I still have no reading from the test wire. I have continuity between the test point and the ecm. Grounding the enrichment valve creates no change in the o2 sensor reading. It's a new, genuine switch.

This is really driving me nuts. I replaced all the sensors with new when I had the manifold off, it has a new wiring harness and WUR, I did not expect this much of a fight.

There is no LH computer. You have kjetronic with lambda control. The lambda controller is the computer you have and it only manages mixture and enrichment using the inputs like the o2 sensor and the enrichment valve. The output is the frequency valve. this controls fuel pressure within the fuel distributor to adjust the engines idle mixture and provide the needed fuel when it sees a grounded enrichment switch. Think of this system as a mechanical type fuel injection with a lambda controller for more precise mixture control.

The constant idle system is the other smaller black box in the right footwell. That controls idle and has a throttle switch reference for when the throttle is closed and has an engine coolant temp sensor so it knows to raise the idle on a cold engine. it also has a feed from the coil for engne rpms. when it senses a closed throttle and the rpms are low. It manages the idle speed. It also has a feed from the a/c to compensate for the load when the compressor runs.

Seems like you want to verify the lambda controller is getting power. There is a larger feed wire to it that is hot all the time. Then there is a smaller red feed wire from the lambda relay which actually is the one that turns it on. I've had the contact at the computer pushed out so it never turns on. If you check out the lambda controller don't check the contacts directly. Open up and remove the cover (it slides down the cable to give you access) and check the contact by back probe or if you are careful you can check from the window on the side. But be careful because there is also a locking tab and you don't want to mess that up or leave a contact pushed away from the computer. It is possible you have a bad controller but it's rare. They are pretty robust.

Thanks for the clarification, I see a box that says bosch and jetronic on it and I immediately think LH.

Is the output to the frequency valve (pin 15) the same signal that I am checking at the red test lead?

I have 8 terminals in the lambda controller (ECU) connector.

#2 oxygen sensor signal (grey)
#4 oxygen sensor signal (thick black, shielded?)
#5 ecm ground (black)
#7 power to enrichment valve and temperature sensor (green)
#8 power from lambda relay (thick grey)
#15 signal to frequency valve (red)
#16 ecm ground (black)
#17 test lead at fender (red)

I've confirmed i'm getting power from the Lambda relay.

edit: not sure about 5 and 16. Diagram just shows the two of them terminating nowhere and I assumed ground. 5 has no voltage, 16 outputs 6.5v or so on startup and falls down to 1.5v or so after a few minutes. I dont have the greenbook for this so I'm relying on the shop next door's alldata account.

What you are seeing on the red test lead is the duty cycle aka dwell of the control signal going to the frequency valve. I could swear there was another power feed but I may be confusing it with the LH jectronic boxes.
Duty cycle is measured at 0-100 percent. Dwell is measured at 0-90 degrees. So 50% duty cycle equals 45 degrees dwell.

Don't want you to think that the signal to the enrichment valve is at 12v. It is pulled up or has a bias setup on it like Art wrote so that the computer can tell when the valve grounds the wire. It has to have a reference so it knows the signal went low.

There is not a temp sensor per se. It is a thermal cut out switch. When the block temp goes below 60 degrees that switch also grounds out the terminal 7 to tell the computer to enrich the mixture due to a cold engine. The real negative coefficient temperature sensor is used by the constant idle system. The thermal cutout and the coolant temp sensor are at the back of the block just above the starter. the thermal cutout is one single terminal. The coolant temp sensor is two terminals.

I wonder if there is a swapped connector somewhere giving the computer a false signal? I would take some time to verify things are connected to where they are supposed to be. Just a thought.

Ok, that makes sense why they are in series. When its cold, the enrichment is just on all the time. Once it's warm, the enrichment switch activates in boost because the thermal switch is closed.

I still don't get any signal at that red test lead, or pin 17 at the lambda controller. I tried a spare test controller and its the same deal.

I really don't want to take the manifold off again, but I don't know what else to try. When I put in the harness it looked like it wasn't possible to swap connectors because of the layout.

The frequency valve is sent 12v power along with the control pressure regulator and idle valve. All from the lambda relay. The computer through a duty cycle signal opens and closes the frequency valve so it can adjust the pressure internally in the fuel distributor.

If you watched it on a scope. You would see a square wave on the freq valve on the wire from the computer. At 12v it equals the other 12v so the valve is closed and if it was at 0v then it would make the freq valve fully open. In between would be various amounts of opening the valve to control the mixture. Which is the amount of dwell you see on the red test lead.

Are you sure you are on the correct red lead? It is supposed to have a black cover on the connector. Sometimes it is tucked under the ignition box so you can't see it. The other red wires around that area are used for 12v feeds for stuff and you won't see anything there but that 12v.