I think I've managed to clean out my very neglected, but low-mile CA18DE.

I put all of my DET parts on it, and am running 8-9 lbs of boost. It pulls really well.

But when I accelerate really hard and then shift, it will make a loud pop out of the exhaust when I engage the clutch. This was never there before. The same thing will happen eventually if I have it in high RPM without my foot on the gas (engine braking).

It doesn't happen if I ride the clutch when I shift. I suppose I could not accelerate so fast, but that's never going to happen.

I tried playing with the fueling settings on my VPC, but that didn't help.

It never did this when I had the DET (lower compression) engine. Other than higher compression, the only other difference is that I'm running the DE exhaust cam (same specs as the DET exhaust cam) on the intake advanced 10 degrees like the tutorial for the cam swap says.

Does this mean I need to retard my timing a little or should I not worry about it? I bought this engine to rebuild it, but it's running so well lately I kind of don't want to now. The sound itself doesn't bother me.

Thanks,

Darian

I wouldn't worry about it too much. My CA did the same thing on the stock ECU, stock turbo, stock turbo manifold, with a FMIC and a 3" turbo back exhaust. When I switched to a tubular manifold, T28 and standalone, it went away. I THINK the stock ECU retards the timing way back when it cuts fuel. I suspect the stock ECU may not completely turn the injectors off as well. My theory is that the really lean mixture combined with retarded ignition timing causes the fuel to burn so slowly that it's still burning when the exhaust valve opens and you hear pop. That's just a guess on my part though.

BOV vented to atmosphere?

BOV is to the atmosphere, but the VPC replaces the MAF with a MAP.

Float, are you sure you didn't mean to write a rich mixture, or am I missing something. A rich mixture would maybe leave some gas behind.

I forgot to mention that I have a different exhaust manifold and my exhaust down pipe is bigger. I didn't think that mattered, though.

One more reason to go standalone. I will, one day.

Good to know that it's not a big deal, though.

Thanks

No, I mean lean. If you have an AFR gauge, you should see that it goes lean when you lift the throttle. Lean mixtures are harder to ignite and when they do ignite, they burn much more slowly. Can you take a video of it?

Oh right, VPC... you're taking your MAP signal off the manifold after the throttle body, yes?

Popping on decel in gear and on upshift might be a maladjusted TPS that isn't triggering the idle switch. ECU won't cut fueling on the overrun unless it sees the idle switch signal.

What happens if you accelerate hard and instead of shifting gear just clutch in, throttle off, and let the engine return to idle while you coast in neutral?

You're right about the VPC.

The sound comes when I hit the clutch and it goes into neutral. Only if I've been hitting hard.

I video is a good idea. I'll have to wait until the weekend, though.

First thing I would try is double check your idle switch is being triggered when you're off the throttle completely. There's a procedure for this in the FSM.

You're dumping raw gas out the tailpipe when the throttle snaps closed, basically. The ECU should be cutting fuel until you drop back down to idle RPM or you open the throttle again but sounds like it may not be.

Another issue you've got is that the VPC is, well, "dumb". You've only got knobs for Idle, and the whole curve in general (gain), which makes it pretty useless if you can't tweak different areas of the fuel curve.

He's right about the idle switch. If the TPS isn't properly adjusted, the ECU may not be turning the injectors off like it should and you would get a lot of fuel into the exhaust, which may be hot enough to ignite it and cause the issue. If that's the case, you need to fix it, as that would likely be occurring in the manifold, before the turbo. That ignition before the turbo would be VERY hard on the turbo.

Thought I had on tuning with the VPC:

Your ECU has a MAF voltage scale that roughly represents airflow. It is an exponential looking curve, not a straight linear scale.

So how does the voltage output from the VPC match up with MAF voltage curve? I suspect it doesn't, as it's a "universal" product. Which means it's likely the ECU's reading of engine load is going to be off by a significant margin and your gain adjustment doesn't offer enough resolution to properly compensate for errors.

Your timing could also be way off, as load for ignition timing is totally dependent on MAF voltage.

Which means, to properly run a VPC you need to build your load scales and fuel/ign tables from scratch to match up with what the VPC outputs, and possibly redo your MAF voltage scale as well.


The more I ponder this device the more I think you'd be better off with a Z32 MAF and Nistune. You're just creating a bunch of extra complexity in your setup.

I agree with you Buddyworm, but there is no room for a MAF. I will eventually get an aftermarket EMS to eliminate this. I love the engine, the EMS is showing it's age, though.

If by idle switch you mean the idle control valve, that broke years ago and I don't use one.

The TPS might be off. I haven't really messed with it, but it worked before. I'm not even sure how to adjust it, but I know it's in the manual.

Buddyworm, you're wrong about the VPC. Every VPC is vehicle specific. They all have different ROM's in them so that they do create that rough sort of exponential curve that matches the curve of the stock MAFS.

Oh cool! Thanks for the info Float. Those crazy Japanese and their addon boxes.


And dhen, I'm not talking about the idle control valve, I'm talking about the TPS sensor itself.

The TPS sensor has two functions: 1) Track the degree and speed of throttle opening, this is the 0-5v signal it sends to the ECU. 2) Trigger closed loop idle control and injection cutoff on decel and gear changes, this is a switch that is triggered when the throttle is fully closed or resting on the stop. #2 is what I call the Idle Switch.

A maladjusted TPS will work properly, but may not be triggering that idle switch when your throttle is closed. You adjust the TPS separately from the throttle itself so that when the pulley is resting on the stop it triggers that idle switch and tells the ECU to cut fuel (or switch to closed loop idle control)

I vote standalone

boost_boy wrote:I vote standalone

QFT

seems like its running too close to perfect, to go thru all the hassle and expense of a standalone
If "old electronics" were haunting u, or big power was in the future...... then standalone probably worth it
Tooooo many excellent performing CA18 still out there on simple 'chip' tunes
VPC not very common on these motors. AFM couldn't go in cold pipe before the throttle body I'd imagine ?

This is in an MG. The fact that he even got the damn thing in there in the first place is borderline miraculous. If he says the AFM won't fit, I believe him. And regardless, it ran fine with the VPC before the engine swap, and the only difference between the two engines is the lack of oil squirters, lack of crank girdle (unless he swapped it over?) and the higher compression. I can't think of how those changes would affect what is obviously a fueling/timing issue. So in my mind, it has to be some sort of sensor error.