V6 running rough.The micro-switch on the intake body? What does it do? - Page 2 - Alfa Romeo Bulletin Board & Forums
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post #16 of 33 (permalink) Old 08-19-2018, 08:09 AM
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If your feeling brave, you can wand an unlit propane torch around the air hoses. RPMS pick up at the leak. Other do this with spray carb cleaner on the hoses, but that can be messy.

Good luck.

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post #17 of 33 (permalink) Old 08-19-2018, 08:10 AM
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You can test a narrow band O2 sensor by holding the tip in a propane flame with a volt meter connected between the output wire and sensor body. The voltage should swing between 0 and 1 volt as you move the tip into different parts of the flame. You can buy sensors with 1, 2, 3 or 4 wires so it is possible to connect one incorrectly if it is not a direct replacement.

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post #18 of 33 (permalink) Old 08-19-2018, 09:33 AM
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I would strongly suspect a large vacuum leak or similar. Since you recently had a shop do all of that work, bring the car back and have them do a smoke test of the intake system---this will quickly locate any and all vacuum leaks. They all need to be repaired before any kind of fine-tuning of the mixture or idle speed can take place. Also make sure the auxiliary air valve is all the way closed when the engine is warmed up!

The oxygen sensor system on the early GTV6 is very basic. The zirconia oxygen sensor needs to be heated to about 500-600 degrees F to generate a voltage and have influence on the air-fuel ratio ('84 and up GTV6s use 3-wire heated oxygen sensors to help them warm up faster).

Get your open-loop mixture and idle-speed settings dialed in before worrying about the O2 sensor. With a 100% properly tuned engine, closed-loop O2 sensor operation will result in a slight wavering of the idle speed on these crude, early systems (Porsche 911SCs of the same vintage do the same thing). Drastic hunting usually means that the base mixture is off, the O2 sensor is out of range, or both.

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post #19 of 33 (permalink) Old 08-19-2018, 09:38 AM
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Have you checked the actual cam timing?

Get Steve's timing chart off the 164 forum sticky. Makes it really easy to do.

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post #20 of 33 (permalink) Old 08-19-2018, 09:46 AM Thread Starter
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...Al Mitchell who raced a GTV6 with modified L-Jet found it to be limiting and he switched to Megasquirt. Al dyno'd a 3L motor, first with L-Jet and then with Megasquirt and with no other changes it made an extra 30 HP. About half of the gain is from eliminating the AFM and half from improved fuelling.
30hp is a solid 10-15% gain over stock. Do you know what he modified on his L-Jet before the switch to MegaSquirt?
- Art

2007 Aston DB9, 1994 Alfa 164 LS, 1982 Alfa GTV6 Balocco SE, 1975 Maserati Bora, 1967 Plymouth Satellite convertible, 1965 Plymouth Satellite hardtop
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post #21 of 33 (permalink) Old 08-19-2018, 09:49 AM Thread Starter
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.. sensors with 1, 2, 3 or 4 wires so it is possible to connect one incorrectly if it is not a direct replacement.
Thanks. It is a multiple wire sensor (I think three). (Two) of them are capped off. One runs up to the connector.
- A

2007 Aston DB9, 1994 Alfa 164 LS, 1982 Alfa GTV6 Balocco SE, 1975 Maserati Bora, 1967 Plymouth Satellite convertible, 1965 Plymouth Satellite hardtop
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post #22 of 33 (permalink) Old 08-19-2018, 10:00 AM Thread Starter
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Originally Posted by Neil Martin View Post
If your feeling brave, you can wand an unlit propane torch around the air hoses. RPMS pick up at the leak.
Good luck.
This I can do in 5 minutes. I'll give it a try while I wait for the new rubber intake trunk...

UPDATE - The propane test was negative-to-inconclusive. I ran the car 6 miles to warm up. Tested rough running with O2 sensor connected and smooth running without. Parked in driveway, at 900rpm idle with O2 sensor connected. I tested propane directly into fresh air intake and got a distinct rise in RPM. Cupped my hand to trap propane around various necks and hoses and hose connections, but got nothing similar. Pulled the vacuum advance hose and directed propane into the port, but got no RPM rise, it's not drawing any air for spark advance at idle.

The inconclusive part was when I connected the O2 sensor, and the idle spontaneously started "hunting" several times, which suspended the propane testing until the idle settled down. I also tested with O2 sensor disconnected. No different propane results.

Not over til it's over: It leaves me with some questionable hoses though, so I'm going to remove them from the car for closer inspection. Thanks for the suggestion.
- Art

2007 Aston DB9, 1994 Alfa 164 LS, 1982 Alfa GTV6 Balocco SE, 1975 Maserati Bora, 1967 Plymouth Satellite convertible, 1965 Plymouth Satellite hardtop

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post #23 of 33 (permalink) Old 08-19-2018, 12:49 PM
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Quote:
Do you know what he modified on his L-Jet before the switch to MegaSquirt?
He had a bench setup where he could simulate all of the signals into the CPU and he knew what Tom Zat had changed and he went on from there, changing components on the CPU board.

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post #24 of 33 (permalink) Old 08-19-2018, 05:35 PM
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FYI, you can also have vacuum leaks at the injectors. There is a rubber washer under the injector body that can deteriorate, this leak can usually also be diagnosed by a plug reading. You may want to borrow or beg a real wideband AFR gauge to do some testing.

When you don't have enough data you can swap out one item at a time to test with. AFM, ECU etc.

Greg

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post #25 of 33 (permalink) Old 08-19-2018, 09:29 PM
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Besides being much safer than propane, smoke testing is the only reliable way to find vacuum leaks (spraying carb/brake cleaner is somewhat effective), and it is why professional shops invest money into smoke-testing machines. That said, I have heard of DIYers renting party smoke machines and even using exhaled cigarette smoke to do the same!

Wideband air/fuel ratio setups are cheap these days, so any serious DIYer with an older car should invest in one of these. That way, you would know if your poor running is a result of a lean running condition (most often caused by vacuum leaks if at the idle/lower speed range) or something else.

Chris A: '81 GTV6 rescued from junkyard, "GT" car/'86 Porsche 944 Turbo track/street car/'73 BMW 2002tii fun street car/'74 Jensen Healey Lemons Rally car!

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post #26 of 33 (permalink) Old 08-24-2018, 08:01 PM Thread Starter
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New rubber trunk, no improvement. Leaks and O2 sensor next.

Thank you very much guys,
..for your myriad recommendations, I have a lot of catching up to do...


VACUUM LEAKS:
- Today I put the new rubber intake trunk on.... There is no improvement.
- I have a smoke machine for Halloween.. I'll try it on a cold engine tomorrow so the cooling fan(s) doesn't blow the smoke all over..
- I'll find out what the Aux Air Valve is and check it, I haven't heard of it before.

O2 SENSOR:
- I'll perform the propane torch test tomorrow and see what voltage I get from the sensor.
- It is one the few things changed during the recent work that has a direct impact on air/fuel ratio.
- The engine runs great with it disconnected.
- If the mechanic kept my old O2 sensor, I'll have him check it (which he might have done when he decide it best to replace it). If it was junk, then the car may have been set up to run without O2 signal and I'll reset mixture and idle without the 'new' O2 sensor. This could be consistent with the mechanic suspecting the ECU has a non-factory map. I'm sure he'd be happy to set up an AFR gauge to check.

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Originally Posted by cda951 View Post
...before any kind of fine-tuning of the mixture or idle speed can take place. Also make sure the auxiliary air valve is all the way closed when the engine is warmed up!
- The mechanic went through the settings after installing the 'new' O2 sensor and checked idle. After that I assume the AFM, ECU and L-Jet all cooperated to achieve the correct mixture for the conditions.. (unless it's tricked by bad O2 signal)?
- I'll search for info on the Aux Air Valve, never heard of it.

Quote:
Originally Posted by cda951 View Post
The oxygen sensor system on the early GTV6 is very basic. The zirconia oxygen sensor needs to be heated to about 500-600 degrees F to generate a voltage and have influence on the air-fuel ratio ('84 and up GTV6s use 3-wire heated oxygen sensors to help them warm up faster).
This is consistent with my problems, which only occur at full temp. That's when the engine starts running rough. My interpretation of this is, it coincides with the moment the O2 sensor comes alive.

Again - the engine runs perfectly under three conditions:
1.) When the engine is cold.
2.) With throttle position at more than 80%.
3.) With the O2 sensor disconnected (although hot idle increases by 1000rpm).

These 3 conditions are when the ECU/L-Jet system calls for "full rich", and the O2 sensor is inactive.

Quote:
Originally Posted by cda951 View Post
Get your open-loop mixture and idle-speed settings dialed in before worrying about the O2 sensor.
This is what my mechanic worked on. Then I had to come take the car.. He got the basics dialed in, got it to run well enough and then I came and got it. We both assumed the issue was minor and we'd figure it out over the phone..

The mechanic remains involved, happy to take my calls, and I'm cross-checking his ideas with your recommendations..

Thanks again, guys,
- Art

2007 Aston DB9, 1994 Alfa 164 LS, 1982 Alfa GTV6 Balocco SE, 1975 Maserati Bora, 1967 Plymouth Satellite convertible, 1965 Plymouth Satellite hardtop

Last edited by 76Satisfaction; 08-24-2018 at 08:06 PM.
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post #27 of 33 (permalink) Old 08-24-2018, 08:08 PM
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I have two Milanos and sometimes one of them runs on five cylinders from time to time. I would check spark plugs, compression test, remove cam covers and check timing, check spark plug wires before checking other parts. I purchased a Milano factory service manual when I bought the Verde and it is very good for locating problems. I purchased many spare parts for both Milanos and both are still running.
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post #28 of 33 (permalink) Old 08-24-2018, 08:42 PM Thread Starter
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...runs on five cylinders from time to time. I would check spark plugs, compression test, remove cam covers and check timing, check spark plug wires before checking other parts...
Thanks! That's what it felt like, so I ran through most of your suggestions early on and I *did* discover a loose spark plug wire at cyl 5 with evidence of arcing, so yes that was a problem..
- Art

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post #29 of 33 (permalink) Old 08-27-2018, 01:09 PM Thread Starter
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Focusing on the O2 sensor..

GIVENS: Engine at idle, engine temperature hot.

- When I measure the O2 sensor voltage while it's wire is connected (to the ECU), the voltage is VERY stable right around 0.525.
- When I measure the O2 sensor voltage while it is DISCONNECTED, the voltage varies.. between 0.60 to 0.80...
Does this voltage Stability vs Variation mean anything?

More O2 Sensor checks:
A.)
- I pulled the O2 sensor and aimed a propane torch at it, and depending on where I aim the torch, the voltage reads from 0.10 to 0.91v.
- Took the car for a 1/2 hour country and highway drive, with O2 sensor disconnected it ran fine. Stopped and let the car idle, measured voltage output of the O2 sensor disconnected, and it reads 0.58-0.61volts. Idle rpm was stable.
B.)
- I drove it 1/2 hour home, again with O2 sensor disconnected. It ran fine.
- Measured idle voltage again in the driveway and it varied from 0.80 to 0.70. Idle rpm was stable.
C.)
- I connected the O2 sensor and drove it 10 minutes. It ran rough, lacking power. When I floored it, it ran fine.
- When I got home to my driveway, I reconnected the O2 sensor and measured the voltage at idle, it was rock stable at 0.525-0.520.
- I compared O2 sensor voltages at idle, connected vs disconnected and found very different results..

Vacuum Leak checks:
- The removed the AFM and air filter housing, applied smoke into the intake trunk with a little positive pressure. No smoke came out anywhere.
- I reinstalled the AFM and air filter housing, started the engine and applied smoke. No smoke was "inhaled" anywhere.
I don't think I have an air leak significant enough to be the root cause.

I'll read through the links on L-Jet before I go further..
Grazie,
- Art

2007 Aston DB9, 1994 Alfa 164 LS, 1982 Alfa GTV6 Balocco SE, 1975 Maserati Bora, 1967 Plymouth Satellite convertible, 1965 Plymouth Satellite hardtop
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post #30 of 33 (permalink) Old 08-29-2018, 10:58 AM Thread Starter
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Bad O2 sensor? Oscilloscope

Baby steps..

Trying first to eliminate the O2 sensor as a problem, I went to a neighbor with an oscilloscope and checked the signal - got a very flat signal at 0.70volts. There was a 'pulse' to the voltage line, but this pulse was barely a wiggle on the "sine wave" at 500mv sensitivity..

We tried it with the O2 sensor connected to the ECU, and it gave the same flat line, just a different voltage 0.50v.

Any comments that the O2 sensor is toast?
- Art

2007 Aston DB9, 1994 Alfa 164 LS, 1982 Alfa GTV6 Balocco SE, 1975 Maserati Bora, 1967 Plymouth Satellite convertible, 1965 Plymouth Satellite hardtop
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