Trigger return with cam sensor?

[gross polluter]

I'm currently running sequential code on my Volvo 245 using the factory Bosch trigger return distributor with the addition of a cam sensor tooth on the cam gear at 65 degrees BTDC. I have my ignition settings as a toothed wheel (4 tooth @ cam speed and 1 tooth at cam speed)

I get a light surge on the freeway and noticed that RPM occasionally drops out. Theres no lost sync reported any time this happens. It seems that this trigger configuration may not have a high enough resolution to maintain timing stability in certain operating conditions?

I'd imagine this configuration would be much more accurate if I could set up my ignition settings as trigger return with the addition of a cam sensor instead of toothed wheel. I noticed 4/1CAS works like this, however, I can't define the location of the cam tooth in those settings.

What do you all think?

[Matt Cramer]

I doubt it's a resolution issue - lots of people run 4 tooth distributors without this sort of problem. Please post a data log of this problem happening, along with your MSQ file, and I can take a look.

[gross polluter]

Here's a log of a dyno pull with the resulting dyno sheet and MSQ. There's nothing in the log that indicates an issue, but you can see the dips in the dyno sheet where this problem is happening. Same thing happens around 2700 rpm during freeway driving, it's a momentary loss of power you can feel, but nothing shows up in the logs. Doesn't happen during street cruising.

Engine should pull to 6000rpm on the dyno, falls flat at 5300ish as if there was a rev limiter in place. Ignition components are all new except for the coils (FC Leading coils)

[Matt Cramer]

Does this hesitation happen if you turn off sequential injection?

[gross polluter]

That's a good question. Haven't tried that yet, actually. I'll switch it back to simultaneous non-sequential (what I had run flawlessly before) and report back with my findings.

[gross polluter]

Switched to untimed injection. 2 squirts / cycle simultaneous which I had used before switching to sequential. Could not get it to replicate the random bucking I experienced in sequential mode.

Very interesting. Any criticism for my injection timing map? Doesn't seem like a lot of people are experiencing the same problem.

[racingmini_mtl]

I don't know if this is what you intended to do but unless your injectors are far away from the intake valve, you are injecting on an open valve at low RPM and then you retard it and inject later which means the pulse finishes after the valve has closed.

With an end-of-pulse timing, I would expect to see timing being advance as RPM increases. Did you do some testing to see what the engine liked best in terms of timing at different RPMs?

Also, I see you are using the trim tables and only trimmed injector 3 a little at higher loads. Was that done to correct something you saw and, if so, how did you determine what was needed?

Jean

[gross polluter]

My intake cam opens at 35 atdc (.050") and closes 25 deg abdc (.050"). If I recall correctly, using the chart on your website under sequential code, that would mean my intake cam opens at 325 degrees and closes at 155 degrees.

The method I was trying to use is at lower rpm and loads is end pulse right before the intake valve opens (340-360) and progressively move the end pulse towards intake closing to keep the entire pulse within the duration of intake valve opening (325-155). I guess I'm doing it wrong? I havent really tried anything beyond tuning lower loads and idle to make it as smooth as possible which resulted in the 340-360 timing figures at the 800 and 1000 rpm bins.

Injector 3 (cylinder 4) is slightly trimmed at higher loads because that cylinder had been showing signs of knocking on the dyno while the rest seemed to run clean. I put a little more fuel in that cylinder to keep things cool.

[racingmini_mtl]

Now I see what you want to do but there are 2 things to take into consideration. First, it takes a certain amount of time for the fuel to reach the intake valve so even if you wanted the fueling to end at the same time relative to engine position you'd still need to advance timing as RPM increases. How much will depend on the injector type and position and the intake configuration so you need to experiment to find out what it is in your case. But the values you have currently will most likely mean the fuel reaches the intake valve after it has closed.

The second point is that this may not be the best setup for your engine and you won't know until you try something else. It could have a noticeable effect. So that combined with the retarded timing might be enough to cause what you're seeing. But you also want to make sure you don't have any other configuration issues with AE which is a very frequent cause for hesitations and stumbles (with wrong injection timing potentially amplifying those).

Jean

[gross polluter]

After doing a little reading on tuning injection timing I realize I've been overlooking the time it takes for the fuel to reach the intake port. When I put the car on the dyno this week I'll mess around with injection settings at higher loads and see what produces the richest AFR. After taking that into consideration, it's almost certain I'm ending the injection pulse over a closed intake valve.

[gross polluter]

Just wrote a different injection timing map to see if another quick idea works.

Started with 420 degrees at idle to end the injection pulse before the intake valve opens (389 degrees on the new cam.) Off idle the timing backs off to 249 degrees at 2000 RPM, which ends the pulse at the lobe center, SHOULD be plenty of time at 2000 rpm for the fuel to travel 70mm within a 111 degree window. I read a post on the motec forums that said a good start to advancing injection timing is 20 degrees per 1000 rpm. I applied this advance to my table from 2000 RPM and took the car for a drive. World of difference. No more surges or quick drops in power. No more cutting out at 5300 rpm. A little more advance is needed past 5000 rpm as it leans out pretty bad at that point, but the issue for the most part is gone. I think this will give me a better start to tuning my injection timing.

Thanks for the help guys!

[racingmini_mtl]

That sounds like a better start indeed. I don't know what you've put for low load at more than 2000 RPM but you probably want something that will also inject on a closed valve for better fuel economy.

Jean