Drifting dwell readings

[Fox2506]

My old post was about the erratic idle caused by the window switches, which was solved with a new idle ECU. That thread seems dead now, but I still have an issue that was blanketed by the latter.

I have been driving around with my dwell hooked up to the lambda system. After putting in a new O2 sensor I've seen the following numbers in chronological order:

Start: 54
Idle: 45
Driving 30-50
Idle: 30-60
Idle 10 sec: 25-50
Idle 30 sec: 18-30
Idle 1 minute: 11.5
Idle 2 minute: 45 (ecu gave up)

When it drops below 20 does rev up. Pressing the full throttle switch brings it to 53 which is good.

I adjusted the throttle plates to let in more air (seemed to help). I have adjusted the mixture countless times, and the engine only wants to run properly at the point where the dwell reads 11.5 (45 when it gives up). If I lean it out to get it close to the desired 35-45 range it just dies.

No vacuum leaks, and no apparent bad grounds. It's all new.

I'm about to give up. Could the Lambda computer be malfunctioning? O2 sensor not grounding properly?

[Elvis]

My old post was about the erratic idle caused by the window switches, which was solved with a new idle ECU. That thread seems dead now, but ....

I'm about to give up. Could the Lambda computer be malfunctioning? O2 sensor not grounding properly?



Well you did not even reply to my offer to repair your ECU for free !!!!!!!


Your mixture can be off an the Lambda system is just doing its job.
I doubt that the Lambda ECU is failing, at least I have not seen one yet.

Take an Oszilloscope and measure the voltage of the O2 Sensor. Maybe a
multimeter works, too, but I'd prefer an O-Scope.

Sounds related to heat or do the spark plugs have a problem ?

[Fox2506]

Well you did not even reply to my offer to repair your ECU for free !!!!!!!


Your mixture can be off an the Lambda system is just doing its job.
I doubt that the Lambda ECU is failing, at least I have not seen one yet.

Take an Oszilloscope and measure the voltage of the O2 Sensor. Maybe a
multimeter works, too, but I'd prefer an O-Scope.

Sounds related to heat or do the spark plugs have a problem ?

Oh sorry, I opted for the updated ECU and couldn't wait.

I wouldn't rule out the lambda comp. After all, who expected the window switch>ECU glitch.

What am I looking for at the O2 sensor? Does it range between 0-1V?

Spark plugs? Guess I'll check them + timing next.

I understand raw gas can build up in the muffler. I noticed a gurgling sound today. Wonder if running rich may have done that, but I'd think it would evaporate.

An injector test indicated 2 cylinders were a little lean, but not much imo. May rerun the test.

[Bitsyncmaster]

What I have found with a drifting dwell is a plugged exhaust system. Although it's a little more extreme than what you are seeing. I would suggest you check your CAT. That means you need to pull it out.

[David T]

What I have found with a drifting dwell is a plugged exhaust system. Although it's a little more extreme than what you are seeing. I would suggest you check your CAT. That means you need to pull it out.

One possible cause is bad injectors. At idle you would get incomplete combustion and the O2 sensor would be swamped by an over-rich condition. The point is the motor must be in good tune or you cannot set the duty cycle. Typically a plugged cat would be noticeable at high RPM's by a dropping off in power.

[Fox2506]

The car did run rich for a long time. I suppose this could cause that gargling sound? Not hard to pull the cat on a stage 2. Or just do a back-pressure test.

[jawn101]

The car did run rich for a long time. I suppose this could cause that gargling sound? Not hard to pull the cat on a stage 2. Or just do a back-pressure test.

If it was really rich for a really long time, the O2 sensor could be fouled and need replacing too.

[Fox2506]

If it was really rich for a really long time, the O2 sensor could be fouled and need replacing too.

I did just replace it, thinking it was the issue. It may have helped a little.

[Fox2506]

Driver side cat looks clear, using a flashlight and mirror (I can see the square pattern/it's not caked over). Perhaps other parts I can't see are clogged though.

I noticed that the input side smells rich like paint or something and the output side has no smell. Same smell I get in the cabin when idling at a stop sometimes. The input side of the catalyst is black, and the other side is white. Just want to get some input before I put it back in.

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[Bitsyncmaster]

Can't see much in that photo. The square catalyst should look white or light brown on a normal car. Your looking to see if the square holes are plugged on the engine side.

[Fox2506]

I can't get a better view inside the cat.

Did an injector test. Two 60 second trials at full throttle. For the second trial I swapped 5 and 6, as well as 2 and 3 at the distributor. Injectors stayed in the same bottles.

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[David T]

I can't get a better view inside the cat.

Did an injector test. Two 60 second trials at full throttle. For the second trial I swapped 5 and 6, as well as 2 and 3 at the distributor. Injectors stayed in the same bottles.

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As important as it is for all of the injectors to flow the same amount, the spray pattern is very important. If an injector is not atomizing the fuel, you can see a jet of fuel squirting out and not a fog of droplets, that is not good also. You should have the injectors cleaned.

[DMCMW Dave]

As important as it is for all of the injectors to flow the same amount, the spray pattern is very important. If an injector is not atomizing the fuel, you can see a jet of fuel squirting out and not a fog of droplets, that is not good also. You should have the injectors cleaned.

Have you ever seen a noticeable issue on a car with the injector flowing the correct amount but a bad spray pattern? I know it's to the greater good, but in practicality I believe balance is a lot more important.

Unless you are dyno testing the car I'm not sure a bad spray pattern will be terribly obvious, but if you happen to have one injector flowing 50% of the other 5 it is VERY obvious when driving.

The other thing that will throw you on a flow test is 6 equally crappy injectors. The amount shown in the 6 beer bottles looks pretty good for a minute.

ADDED - you also want to do that flow test at partial flow. I've seen injectors that would balance wide open (Where you never really run the engine) but be way out at 10% flow (where you are driving a lot more often.)

[Bitsyncmaster]

When I did my flow test, I pushed the air plate down about half way. I had one very minor difference on one bottle but it was nothing as much as your showing. I adjusted my FD to fix that one difference.

I'm not sure if the difference you show is common and if it would be causing your problems.

[DMCMW Dave]

When I did my flow test, I pushed the air plate down about half way. I had one very minor difference on one bottle but it was nothing as much as your showing. I adjusted my FD to fix that one difference.

I'm not sure if the difference you show is common and if it would be causing your problems.

Having done a ton of these - A perfect system (6 new injectors, good FD) will flow dead-on the same from all 6. At any pressure. This, along with a nice spray pattern is of course ideal.

The one in the pictures is probably OK unless you are really going for perfection, and I'd guess that not one driver in 10 would notice the difference if you replaced all the injectors. It's common, and if this is a "back from the dead" car it will get better after some run-time and injector cleaner. If this is a now-running driver car, it's as good as it will get.

[Fox2506]

What I find odd is that injectors 5 and 6 were different levels the first time and then they were the same the second time. 5 dropped to normal but 6 did not increase like I expected.

Then, 2 and 3 did alternate like expected, indicating an injector is at fault.

[Fox2506]

Took off my cat and soaked it in solution overnight, hoping to clear any possible obstructions. I also did one more injector test at half throttle this time, and at 60 seconds. Fuel looks fine (seen below). Started up fine and idled ok, but the dwell still did not leave 45. I couldn't go for a test drive though, because the roads are salted...

Going to check exhaust pressure through the O2 sensor port next. If I were to try a temperature check at the cat, does anyone know the temperature specs of the Stage II exhaust?

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[David T]

Have you ever seen a noticeable issue on a car with the injector flowing the correct amount but a bad spray pattern? I know it's to the greater good, but in practicality I believe balance is a lot more important.

Unless you are dyno testing the car I'm not sure a bad spray pattern will be terribly obvious, but if you happen to have one injector flowing 50% of the other 5 it is VERY obvious when driving.

The other thing that will throw you on a flow test is 6 equally crappy injectors. The amount shown in the 6 beer bottles looks pretty good for a minute.

ADDED - you also want to do that flow test at partial flow. I've seen injectors that would balance wide open (Where you never really run the engine) but be way out at 10% flow (where you are driving a lot more often.)

I believe flow and spray pattern are about equally important. If you are flowing but not atomizing, the fuel will just puddle on the intake valve and not burn completley. If the pattern is OK but you are not flowing equally you will not get the motor to idle smoothly. You are right in that I have also seen motors running on a less than perfect fuel system. The point is the better you can get the fuel system to work the smoother and better the motor will run. The best measure is how smooth it idles, how it behaves as it warms up, and what the gas mileage is. The K-jet is very intolerant of dirt and stale fuel. One of the biggest reasons it is hard to resurrect a "dead" car. You have to go over the whole fuel system. That and the brakes/clutch. Those two systems do not store well.