Misfiring and back firing - Alfa Romeo Bulletin Board & Forums
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post #1 of 19 (permalink) Old 08-16-2019, 05:43 PM Thread Starter
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Misfiring and back firing

Hello all,
My '88 Spider Graduate has be running fine till about 3 weeks ago. Now it misfires and stumbles at low rpm and back fires when letting off gas , as in slowing down or between up shifts and idle is a little rough,under acceleration it runs fine. I found the bullet fuse going to the VVT was corroded, and replaced it with a spade fuse/ holder.I also changed the O2 sensor and it does run a little better.I not sure of what to do or check next.

1988 Spider Graduate (Sofia)
'06 Ford Explorer
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post #2 of 19 (permalink) Old 08-16-2019, 06:59 PM
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Look for a leak (called false air) into the intake system, from maybe a split in the rubber tube across the top of the motor, or in the convoluted flex section, or maybe a loose clamp around that hose, the throttle body or the airflow meter. Sounds like it's gulping air from somewhere it shouldn't. Listening by using a small diameter hose, like vacuum hose, and probing around those areas, you can actually hear the hiss of bad vacuum leak. If you have an old fashioned vacuum gauge, connect to the intake manifold and check the vacuum reading. It should read above 14" to 15" hg at idle.

If you find a split hose or tube, you can repair it easily using a product called Shoe-Goo.
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post #3 of 19 (permalink) Old 08-16-2019, 10:10 PM
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Pull your distributor cap & rotor. Mine looked great outside and was badly worn inside. Inspect both ends of the plug and coil wires - deep in the sockets - for corrosion.

My Spider was running rough, and stumbling under part throttle, just last week, and these were all problems. Now it runs strong.

David O'D
Laguna CA
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post #4 of 19 (permalink) Old 08-17-2019, 12:41 AM
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I like the "pull the dipstick" trick to check for vacuum leaks.....
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post #5 of 19 (permalink) Old 08-18-2019, 05:32 PM Thread Starter
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I changed the cap and rotor,checked for air/vacuum leaks again (none ),did the dip stick trick( slight change in idle ).
I still have a rough idle and grey exhaust smoke after warm up.
Could it be a bad air flow meter ?
It looks to be original and the cover has been siliconed on by PO.

Thanx

1988 Spider Graduate (Sofia)
'06 Ford Explorer
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post #6 of 19 (permalink) Old 08-18-2019, 05:40 PM
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Rough idle and grey exhaust color?? Hold your hand close to the exhaust, does it feel moist? Check your coolant bottle, look for a milky or mixed liquid resembling chocolate milk shake in the coolant. With the cap off the coolant bottle, and the engine idling at normal temperature, have someone hold a shop rag over the exhaust pipe, while you watch for bubbles in the coolant. If you see any of these things, let us know.

You may want to pull the plugs and do a compression check also, and report the findings.
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post #7 of 19 (permalink) Old 08-18-2019, 05:41 PM
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Have you compared all your plugs? Compression test? Flywheel sensors and connections? Those AFMs are pretty durable, I would check all else before considering it.
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post #8 of 19 (permalink) Old 08-18-2019, 06:18 PM Thread Starter
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No chocolate in coolant or oil. The exhaust is not moist or smell like coolant and level in coolant bottle hasn't changed.
This condition just started one day while driving I down shifted at a curve, and engine stumbled and began to misfire at low rpms.
I'll check those other suggestions and let you know.

1988 Spider Graduate (Sofia)
'06 Ford Explorer
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post #9 of 19 (permalink) Old 08-21-2019, 01:13 PM Thread Starter
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Are both flywheel sensors the same part? I know each has a specific plug on the harness , black upper ,grey lower. How hard are they to change if I jack up front of car or roll up on ramps ?

1988 Spider Graduate (Sofia)
'06 Ford Explorer
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post #10 of 19 (permalink) Old 08-21-2019, 01:37 PM
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Quote:
Originally Posted by quartrsawn View Post
Are both flywheel sensors the same part? I know each has a specific plug on the harness , black upper ,grey lower. How hard are they to change if I jack up front of car or roll up on ramps ?
They are the same part no. Good prices at Rock Auto.

Rich

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'17 Giulia Ti Sport
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post #11 of 19 (permalink) Old 08-21-2019, 01:44 PM Thread Starter
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I purchased 1 from Rock Auto , I suspect I have a bad one. I have to ohm check them .

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'06 Ford Explorer
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post #12 of 19 (permalink) Old 08-23-2019, 02:20 PM Thread Starter
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I ohm checked the flywheel sensors, they seem good both have same reading.Rechecked all air/vacuum hoses. I found one of the clamps on an intake runner hose to be very loose. I had them replaced when the shop replaced my motor mounts this past fall, guess it wasn't tight enough. Tightened it and checked all the others,started up and the idle sounds better and is smother.I road test tomorrow,looks like rain now.Still getting grey/ "too rich smoke".

1988 Spider Graduate (Sofia)
'06 Ford Explorer
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post #13 of 19 (permalink) Old 08-23-2019, 02:24 PM
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Still sounds like false air to me....
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post #14 of 19 (permalink) Old 08-24-2019, 02:29 PM Thread Starter
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I thought I had the solution , but I think I'm chasing my tail. Still idles rough , misfires ,backfires and grey exhaust smoke. Now I'm wondering if the head gasket is going ?

1988 Spider Graduate (Sofia)
'06 Ford Explorer
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post #15 of 19 (permalink) Old 08-24-2019, 05:55 PM
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Just to check off another possibility, why not do a compression check? It's the grey exhaust you talk about that concerns me.

Before this happened, did you ever hear a scraping or whirring noise from inside the cam cover? What I'm asking is, do you think your timing chain was adequately tensioned?

The coolant temperature sensor is a key input device on that L Jetronic system. Carefully pull the connector off, spray the inside of the connector and the sensor pins with electronics/electrical cleaner, and replace the plug making sure it's seated.

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