Afr goes lean after decel in gear

[mk1rocc]

While driving no I did not, but I did test it on the bench so to say, fuel rail with injectors out and into jars . With the pump on and injectors of I was getting 3Bar with them on also 3bar no fluctuation what so ever...
Do you think that is not conclusive enough, should I watch the fuel press while driving?

[grom_e30]

do you notice a difference in how the car drives when this happens? if so id get a co pilot to watch the fuel pressure gauge.

[mk1rocc]

OOKK , it's finally solved ! Guess what, after trying every setting in MSQ that made sense I finally came to nominal dwell . I changed before but a very small amount +- 0.2 and nothing really happened this time I went from 3.5 to 4 and the car did not want to accelerate at all even from idle the engine rumbled and the afr showed 18 and that was that, so I went the other way first to 27 than to 2.5 and now it revs to 5K easily....so it was that dammed coil pack after all...
Now the question is why such a low dwell? is the coil dying?are the msq drivers overheating?
The coil never got hot it was barely warm to the touch so I dunno...

[kaeman]

What coils are you using? Some of the gm coils don't like dwell in excess of 3.5 ms... they will automatically fire when the are oversaturated to protect the coil. Your coils might have be doing this and firing early, causing you to see lean spikes because of the longer burn time. Glad you got it figured out. I am running my coils at 3ms dwell, they are not having any problems. As long as you are getting good spark short dwell isn't a bad thing.

[mk1rocc]

What coils are you using? Some of the gm coils don't like dwell in excess of 3.5 ms... they will automatically fire when the are oversaturated to protect the coil. Your coils might have be doing this and firing early, causing you to see lean spikes because of the longer burn time. Glad you got it figured out. I am running my coils at 3ms dwell, they are not having any problems. As long as you are getting good spark short dwell isn't a bad thing.

Well I think the dwell wasn't the issue , i noticed that the Spark duration was set to 0.7ms so ,yeah I guess that is the real reason for my issues.
I set it to 0.1 as per manual , dunno if this is optimal or not .I will reset the dwell to 3.2 and see if it works.
The coil is a sagem from a renault.

[mk1rocc]

Well that theory went out the window , after changing the duration to .1ms and the dwell to 3.3 the car stumbled again at about 3.5k so I had to reduce dwell to 2.3 to be able to rev to 5.2k.
So what is the deal... longer duration less stress o the coil.? I thought otherwise...

[strain]

Well that theory went out the window , after changing the duration to .1ms and the dwell to 3.3 the car stumbled again at about 3.5k so I had to reduce dwell to 2.3 to be able to rev to 5.2k.
So what is the deal... longer duration less stress o the coil.? I thought otherwise...

The spark duration need to be set at 1ms, then with the engine at idle lower the dwell until the engine start to stumble, then add 0.3-0.7ms and your dwell will be fine (don't forget to check the dwell voltage correction table).
Let us know how it goes,
Cheers!

[mk1rocc]

Well that theory went out the window , after changing the duration to .1ms and the dwell to 3.3 the car stumbled again at about 3.5k so I had to reduce dwell to 2.3 to be able to rev to 5.2k.
So what is the deal... longer duration less stress o the coil.? I thought otherwise...

The spark duration need to be set at 1ms, then with the engine at idle lower the dwell until the engine start to stumble, then add 0.3-0.7ms and your dwell will be fine (don't forget to check the dwell voltage correction table).
Let us know how it goes,
Cheers!

OK , got it, I'll give it a shot .I'm very curios what is the result...

The dwell correction table is stock i have not touched it:
6v:500%
8:248
10:168
12:128
14:102
16:88
Is that ok?

[strain]

OK , got it, I'll give it a shot .I'm very curios what is the result...

The dwell correction table is stock i have not touched it:
6v:500%
8:248
10:168
12:128
14:102
16:88
Is that ok?

I Saw your log and your battV it's solid at 13.5v that's good, I use this correction without issues.

8:222
10:140
12:122
14:102
16:86

As you have an a stable BattV then the correction wasn't an issue, try the method i wrote in the other post to find the dwell, set the spark duration to 1ms and try how it goes.
Cheers,
Straïn

[mk1rocc]

Well tried the idle technique to set the dwell and came up with 2.3 then tried to set it at lean cruise and got the same number, so I left it that way.
But I have one question : could the coil be damaged in some way ? because at first it worked ok with the dwell set at 3.5 and duration 7 but degraded after a while , so is there any way to determine if the coil is shot ?

[grom_e30]

you could measure the resistance of the primary and secondary winding's in the coil and see if they are withing the manufactures specks or not, id measure them with the coil both cold and hot.

[mk1rocc]

you could measure the resistance of the primary and secondary winding's in the coil and see if they are withing the manufactures specks or not, id measure them with the coil both cold and hot.

I measured the resistance:
Cold : Primary 0.3ohm (seems low to me....)
Sec: 7.35Kohm
Warm: Primary 0.3ohm
Sec: 7.5Kohm

I do not know the factory specs for this coil so can't verify if this is within spec, I did however measure another identical coil and the readings were consistent with mine.

The weird thing is that out of nowhere I got same bog with afr reading 21 , i had to reduce dwell to 2 and the problem went away and hasn't come back yet... It's weird..maybe I should switch to a different coil pack...but I don't know what to go for...