Lost in a sea of tuning... (Ostrich 2.0)

[McGyver]

Can you advise on a recommended cam?

Adding onto this question, FF, can you recommend some reading on how to size a cam to an engine/application using a mathematical approach? You're linked article was really enlightening, but it sounds like they kind of threw parts at it to see what works.

I'm happy to go into detail about my build, but don't want to threadjack here.

[bmwman91]

FF, this is more your area of expertise...has it been your experience that dynamic compression issues like this can cause a full fuel cut situation above certain RPMs? The pinging and otherwise poor running at lower RPMs make sense, but the cut-out at WOT and high PT above ~4000RPM seems (to me) like an indication of something else. But, you have way more hands-on with this sort of thing, so maybe it really can be a function of the cam setup.

[Tinkerer007]

Thank you for the examples.

Can you advise on a recommended cam? (I don't want it too racy as it is street driven. Is a 280 enough? 288? What does it mean if the duration for IN & EX are different ?)
Recommendations on where to get one?

Can it be replaced with the engine in the car?

[ForcedFirebird]

You have too much dynamic compression. When doing a compression test, you need to be about 200psi or less. Since your cam is closing the intake valve too soon, the compression is getting trapped at lower RPM. This is why you have a lazy car when you put a big cam in a stock motor (it "wakes up" in high RPM).

So, what happens is your cylinders are fighting each other since the fuel is self-igniting. You can create ignition just with pressure (think campfire piston igniter), so as the piston is on it's way up, the fuel gets compressed enough to "diesel" before it reaches TDC and interferes with the other piston operations.

Real world numbers from my experience:

Stock tired m20: 155-165psi
Fresh stock rebuild: ~175
Top of the line spec build (max shave on head/block etc): ~185
Fresh rebuild with 272 cam: 145
(all above had 8.8 stock comp)

9.4:1 2.7 with 272: 190 (~4° cam retard from 2mm block deck)
9.4:1 2.7 with stock cam: 205 (~4° cam retard from 2mm block deck)

As you can see by adding a 272 duration cam, the cranking compression drops. So, you really can't deduce static compression directly from cranking compression since the cam and any leakage (valves etc) can change the numbers by a good margin.

When you have a later closing intake valve, some of that pressure gets bled off, same with a lot of overlap.

[Tinkerer007]

Cleaning up electrical connections turned into a rabbit hole. Did get an increase in voltage of .02 volts.
The battery in in the trunk, and the '87 harness is normally grounded to the shock tower (I have it bolted to the battery tray).
The rabbit hole was the battery hold down bolt was broken in the battery tray. It took many hours to grind the rusted nut off and replace the battery tray. On a positive note, the battery area in the trunk is less rusty than I thought it was. And now, it is much cleaner, and the battery is clamped down.

I only have one of each ECU (380, 173).

I was not able to find a spare coil. ( I have tried a second crank sensor.)

The other rabbit hole was researching static and dynamic compression. (I learn so much from the people on this forum.)
I also tried to see if there is a way to figure compression from measured PSI...

https://www.reference.com/science/convert-compression-ratio-psi-825aedc74e6b59d7

This says that you take atmospheric pressure x compression ratio = ~Measured PSI.
14.696 x 10:1 = 146.96
215 / 14696 = 14.629 :1

That seams like pretty high compression. How accurate is this method? It seems like it should be in the ball park.
I think my M30 with 10:1 is around 165 PSI
I think an M20 with 8.7:1 is around 125 PSI

What could be done to get higher compression on my engine?
Surface head
Surface block
I don't think head gaskets can be thinner, but they can be thicker.
Different higher compression pistons
Fill head chamber with epoxy

Is it possible to measure block and head with engine assembled?
What should the numbers be?

[ForcedFirebird]

I believe your issues are too much dynamic compression. With the result of the octane booster and compression test it drives that theory even further for me.

There's nothing wrong with your compression, the cam is just not up to the task.

Static compression is only one factor when building a proper engine.

[bmwman91]

OK, it sounds like you still have multiple issues then. That sort of cut-out is a major indication of a crapped sensor or some other fault wither with an input to, or an output of the ECU.

First, it is good that adding octane booster stopped the pinging. Maybe the cam is "too hot" for pump gas, maybe not. If there is a major control-related issue elsewhere, then it is hard to say if the ignition timing is really being set properly the rest of the time.

Let us know how it goes with the spare 173 ECU and the Sssquid chip (you have 2 correct, not one 380 and one 173?). Also it is good that you got the battery ground tightened lol...that is never helpful to have rattling around!

How does the car run when it is started cold, and does it change as it warms up? The crazy AFR swings really sound like an issue with the analog input to the ECU from the O2 sensor, although that would only be if the issues started when the engine got warmer (and not right away form a cold start). Where did you ground the WBO2 controller and/or sensor? It MUST be grounded on the same lug as the ECU. The NB signal's full range is 150-900mV, so if there is a ground offset of even a few tens of mV between the ECU and where the thing is grounded, it is going to be way off (I learned that the hard way many many years ago). Even still, I would not expect that to cause big swings, just a constant offset.

I didn't see it mentioned in your post, but check the engine-to-chassis ground strap. It is vital. Also, if the engine harness is from an 87 325iS and the car has the battery under the hood, where did you run the ground of the newer harness to? The iS cars had the battery in the trunk normally, and the engine harness grounded on the (empty) front battery tray. I assume you just ran it up to the negative post on the battery? Messed up grounding is a major cause of significant running issues in many cases.

And yes, a dying ignition coil can sometimes cause issues like this. Borrowing a spare could prove helpful. How are the ignition wires? Sometimes the insulation cracks and arcs to the engine.

[Tinkerer007]

Injectors were changed today.
Initially it ran like crap, and it was quite discouraging. After a break and another look, I found one of the connectors came off as I was checking the connection. Re-clipped it in and it ran much better.

The idle is worse. Cycling from rich to lean. 12 - 17 AFR. And the car is hard to get going from a stop.
The acceleration is better, but still cuts out at 3800 RPM. The harder the throttle is pressed the harder the cut is. It feels like a rev limit. One time it even made the tires squeak. It accelerates well if I stay in Low Part Throttle. High Part Throttle it feels like it bogs down, and WOT it cuts out hard.
I am wondering if the coil could also be bad. I have another one I can try.

And the ping is still there. It does go away with $3 of octane boost.

I do have a second AFM that has the same cut out behavior at 3800 RPM.
I do have a second ECU. The original donor car had a 380 ECU, and I have a 173 ECU that I got with a Dinan chip that worked in the previous car.
The wiring harness is out of an '87 325is. The ground on the battery was not tightened down, so I took all connectors off and cleaned and sprayed some batter connection stuff on the terminals.

I also checked the battery voltage. Found 12.42 V at the batter and 12.40 at the cigarette lighter. (That is where the WBO2 gets power.) The ECU was not mounted in the glove box, so the case was not grounded. I mounted the ECU before driving. I got 14.39 volts at the firewall power and engine valve cover.

Thanks for all comments and recommendations.

[bmwman91]

Interesting. Yeah, it sounds like there are still some other underlying issues, with the cam being a little "too hot" as FF noted. I'd see if the octane booster helps with the pinging since it is fast and relatively cheap to do.

When you say "cutting out around 4K RPM" do you mean that it feels weak, or that it exhibits a hard cut / full loss of power? Is it only at WOT, or even at PT? If it is fully cutting out, then that seems to me to be more than an octane issue. Either the injectors are not flowing enough (seems sort of unlikely), the AFM has damage on the carbon resistance track, the hot cams are producing an induction resonance that mixes with the AFM's acoustic-mechanical resonances (it is very much a thing with the M42, but seems less likely on an M20 since 6 cylinders have a lot more overlap), or some other sensor is having an issue.

The O2 sensor info is interesting. Normal operation is to have the AFR oscillate at ~1Hz at idle and low RPM, ~2Hz at most PT operating points, and then to ignore O2 input at WOT or >4000RPM (I think, I can't recall exactly where the open-loop switchover is). So, seeing it go lean/rich/lean/rich is normal and correct. If it is NOT doing that with the wide-band, then there is an issue with the wiring, the sensor or the controller. How EXACTLY did you wire it in? I found that the Innovate products were very sensitive to the ground configuration, or at least the LC-2 was when I used to use one. You should have the analog ground connected on the same lug as the ECU, which is on the battery tray I think (on the M42 E30's anyway). If there is a separate heater ground, I'd connect that to the hood latch (although if your battery is up front and everything is on the negative terminal already, it is probably fine to connect it there). The main thing is to have the analog ground at the same point as the ECU ground though.

See if you can borrow a known good AFM and ECU, and swap each one at a time. The fact that it runs lean with a WB and NB O2 sensor connected is odd. That makes me wonder if the ECU is damaged. Used ones are cheap on eBay. Is the wiring all original, or did the car have a conversion from the older Motronic to the later one? How is the condition of the ground strap which connects the engine to the chassis?

[Tinkerer007]

My SSSquid chip came today.

It does accelerate better. But still cuts out around 4K RPM.

Also, it pings from light acceleration on the freeway. (Didn't used to do that.)

I took it to my mechanic to check the O2 sensor wire that I thought showed 97 Ohms. Turns out I was measuring the wrong pin on the ECU connector. The resistance is .1 Ohms.
It was interesting to watch the voltage on the O2 sensor. It cycles very fast. I also had the wideband O2 sensor and it did not follow the lean / rich readings the narrow band did. It is either slower, or they have smoothed out the readings. At least this verified that the O2 sensor is working.

Next steps are to replace the M50 injectors with the new 19 lbs injectors.
If that doesn't resolve the pinging, then get some octane booster.
And then retard the valve timing.

On a side note, I was browsing for a camshaft, and found some 11:1 compression pistons on IE's "specials" site.
https://www.iemotorsport.com/product...orged-pistons/

It seems like the compression might be more than 10:1.
I have a Euro spec M30 with 10:1 compression, and it is able to idle and run on premium gas without pinging. And a compression test is less than 200.
Is there a way to measure compression without taking the head off?
How much could a thicker head gasket reduce the compression ratio?

[ForcedFirebird]

Yeah, I feel 284 would have been more suited - just as that ad says: "If you’re building a stroker M20 engine with a bit of compression behind it we would recommend going with the 284 grind!"

The m20 is relatively quiet during detonation. You could try and upping the octane with an additive to see if it resolves your problems. If it does, a cam change is probably the best answer.

The intake valve is closing too early, you may be able to help it a little with the adjustable cam gear. Just be aware of valve to piston clearances.

[Tinkerer007]

The engine was advertised as having a 274 cam.
Their website says 274 - 415.

Here is the description:
These cams make an improvement you can really feel. Higher lift helps mid-range power and extra duration helps the top end. These cams will pull right up to 7000 rpm with ease. We have 3 different grinds available. The 274 cam is excellent for mild builds while still retaining streetability. The dual pattern 280/274 is great for those who want something a bit more aggressive than the 274 and also very ideal for boost. If you’re building a stroker M20 engine with a bit of compression behind it we would recommend going with the 284 grind!

[ForcedFirebird]

I didn't notice here, or the other thread, as to which camshaft you are running, but based on those cranking compression numbers, it's on the small side. If those numbers are accurate, you are trapping too much mass, even a fresh s50(2) is 210psi and requires premium fuel (with the benefit of variable cam timing).

Here is a good article explaining how cranking compression can give you some insight:

http://www.superchevy.com/how-to/816...e-compression/

Too Much of a Good Thing
If you're the classic hot rodder, then you're already thinking, "Hey, if some is good, then more is better!" True to form, if you do that, you will be disappointed. Higher cylinder pressure also means that you will need more octane to slow the burn rate in the cylinder. The limit for street engines seems to be around 200 psi of cranking pressure. Numbers higher than 200 psi create excessive cylinder pressure at low engine speeds, which turns the engine into a detonating monster. A classic example of this would be an 11:1 compression engine with a short-duration camshaft that features an early closing intake valve, such as 50 degrees ABDC. This would create excessive cranking pressure and an engine that would rattle its brains out on 92-octane fuel. Our current HT 383 engine actually tested at 195 psi with the original stock cam and later at 185 psi with the large hydraulic-roller cam and does not detonate.

[Tinkerer007]

Here is some more data.

I was trying to figure out why the LM-2 reads the exhaust as lean when it smells rich.
I calibrated the LM-2 O2 sensor, then installed it.
Started the engine. It starts out fine around 14.9, but as it warms up, it goes lean, to 15 - 17 AFR.
If I unplug the O2 sensor, the AFR goes to 14 -15.
I had the original O2 sensor from the donor car, so I installed that. Same result 15-17 AFR.

I measured the resistance from the ECU pin 29 to the chassis O2 connector at 98 Ohms. That seems like a lot to me. Could that be a problem? How do I find where the resistance is coming from?

[Tinkerer007]

Do these plugs look like the engine is running lean? And compression seems okay? Sent from my VS995 using Tapatalk