SC out of Gas

[Race Grandpa I]

At slightly above 6,000 rpms the engine loses all power from the SC. It is like the engine has run out of gas. Previous to this it was suggested that I put in new plugs, which I did. The only thing that putting in the new plugs changed is that it gained about 3 hp


Attached is the graph

[Tom @ Fast Forward]

Can you add A/F to that graph?

How old are your coils?

What is your timing under load on the dyno?

If A/F is good, I'd vote for coils.

[Race Grandpa I]

Here is the other graph.

As for the coils the car has 57,000 miles. However, the coils were not a problem with the #2 SC engine.

I have a new crate motor. Did it come with new coils or did they use the coils from #2 engine.

I will ask tuner about timing.

[Tom @ Fast Forward]

Fuel doesn't look bad enough to cause it. Compression Ok?

I still lean towards coils.

[Race Grandpa I]

I have a crate motor with 1,500 miles. So the compression should be OK.

Did the crate motor come with new coils or did they use the coils from one of the other two engines.

How does one find out if the coils are bad. If I go to a dealership, they surely will put in new coils even if they are not needed.

[Race Grandpa I]

Any more ideas?

[Tom @ Fast Forward]

Paul,

It's relatively simple. If you have proper fuel (and it appears that you do) and you have good/decent compression (and you say it is), the only thing left is ignition/timing. Your shop was on the right track with the plugs but they are seldom the case. What plugs are you using and what gap?

BTW, I am on my third set of coils. First set went at ~70,000 miles. Second set went at about 125,000 and the third set is running very well so far, at 150,000 miles.

The #1 part that fails on stock Miatas is the coils. On boosted Miatas the load is worse. That is why you see people trying so hard to get other coils (GM, Toyota, MSD, etc) to work.

[Steve in VC]

Paul,

If your car can use coils from a 2000, I have a new set I can loan you for the cost of shipping them.

Steve

[Race Grandpa I]

Paul,

If your car can use coils from a 2000, I have a new set I can loan you for the cost of shipping them.

Steve

Thanks Steve. I will go on Mnet and see if I can get answer.

[Race Grandpa I]

Paul,

It's relatively simple. If you have proper fuel (and it appears that you do) and you have good/decent compression (and you say it is), the only thing left is ignition/timing. Your shop was on the right track with the plugs but they are seldom the case. What plugs are you using and what gap?


The plugs you told me to get.

BTW, I am on my third set of coils. First set went at ~70,000 miles. Second set went at about 125,000 and the third set is running very well so far, at 150,000 miles.

The #1 part that fails on stock Miatas is the coils. On boosted Miatas the load is worse. That is why you see people trying so hard to get other coils (GM, Toyota, MSD, etc) to work.

With the SC in the first two engines and prior to taking it to the tuner the maximum mileage on the coils was about 350. Do new coils come with a new crate engine???

[Race Grandpa I]

Maybe - just Maybe - Hopefully the issue is coming from my J&S Safeguard.

If it feels like it is running out of "gas," would this be an indication that the J&S has changed the timing??????

[Tom @ Fast Forward]

No. Coils don't come with a crate engine.

Hopefully, your mechanic knows that you can blow the coils simply doing a compression test if you don't disconnect the power to them.

Pretty sure Steve's coils won't fit your car.


With the SC in the first two engines and prior to taking it to the tuner the maximum mileage on the coils was about 350. Do new coils come with a new crate engine???

[MiataMTF]

Here is the other graph.

As for the coils the car has 57,000 miles. However, the coils were not a problem with the #2 SC engine.

I have a new crate motor. Did it come with new coils or did they use the coils from #2 engine.

I will ask tuner about timing.
Any possibility of a dyno plot that shows boost and AFR?

Since the power curve tails off at about 5500 RPM, it could be timing and/or weak spark. It's unlikely but you might also be a victim of belt slip. Or, do you have a major pressure leak that would explain the flattening of the power curve.

Later, above 6000 RPM, it looks like the AFR is less than 10.5-to-1 - it could be that you have too much fuel and that is quenching the combustion. I think it's best to keep the AFR above 11.5-to-1 which ensures efficient combustion.

Also, your AFR curve (if that's what it is) is a little wonky - the PC-Pro should kick in more fuel well below the 3400 RPM indicated, unless you intentionally set it that way. A boost plot would help diagnose this issue.

Finally, isn't the power curve a little low? Extrapolating the power curve yields approximately 170whp which is low even for a DynoDynamics dynamometer.

When we adjusted the PC-Pros on Hans' '99...it was too rich (about 170whp) and we gained almost 20whp (189whp max) by fine-tuning the fuel delivery and timing.

[Race Grandpa I]

Any possibility of a dyno plot that shows boost and AFR?

Since the power curve tails off at about 5500 RPM, it could be timing and/or weak spark. It's unlikely but you might also be a victim of belt slip. Or, do you have a major pressure leak that would explain the flattening of the power curve.

Later, above 6000 RPM, it looks like the AFR is less than 10.5-to-1 - it could be that you have too much fuel and that is quenching the combustion. I think it's best to keep the AFR above 11.5-to-1 which ensures efficient combustion.

Also, your AFR curve (if that's what it is) is a little wonky - the PC-Pro should kick in more fuel well below the 3400 RPM indicated, unless you intentionally set it that way. A boost plot would help diagnose this issue.

Finally, isn't the power curve a little low? Extrapolating the power curve yields approximately 170whp which is low even for a DynoDynamics dynamometer.

When we adjusted the PC-Pros on Hans' '99...it was too rich (about 170whp) and we gained almost 20whp (189whp max) by fine-tuning the fuel delivery and timing.

The tuner does not have one graph that shows both boost and AFR, which I thought was real strange.

As to the AFR I thought that 12:1 was the max before detonation could occur. Or am I mixing that up with lbs boost?

When I talked to Tom sometime ago I was real worried about losing another engine to detonation. Tom suggested that by cutting the boost back to 11:1 that I would realize about 175 whp. Since I am getting a timing card, I am not so worried. However, I am going to keep the boost between 11 to 11.5

Most everything you are talking about is way beyond me. However, I have found another shop that has a dyno. So when I go there next week I will take your comments. As always Tom is around any questions day or night.

If you have any more info or comments, based upon the info I have given you I sure would appreciate hearing from you.

[MiataMTF]

The tuner does not have one graph that shows both boost and AFR, which I thought was real strange.

As to the AFR I thought that 12:1 was the max before detonation could occur. Or am I mixing that up with lbs boost?...
Depends on how the system is setup and what sensors are used. You should as the dyno operator for the full list (at least: power, torque, AFR, boost, timing).

All things being equal, pinging occurs as a function of boost, intake air temperature, AFR, and fuel octane (octane is a measure of a fuel's resistance to pinging). On 91-octane pump gas, the pinging threshold is typically around 12:1.

...Most everything you are talking about is way beyond me. However, I have found another shop that has a dyno. So when I go there next week I will take your comments. As always Tom is around any questions day or night.

If you have any more info or comments, based upon the info I have given you I sure would appreciate hearing from you.
You've definitely gotta find a shop that will do good by you. There's are plenty of reasons for a poor-running forced induction setup. I've tinkered with turbos and SCs for VWs, Hondas, Toyotas and the Miata. There's a lot to be said for "install, set and forget" but it seldom seems to be that easy. I may not remember every little bit but here are a few tips:

The first step is to ensure that your system is mechanically correct including: no vacuum or pressure leaks, good belt tension (no slippage), exhaust is not blocked by a clogged catalytic converter or other obstruction. This includes making sure that the air-fuel meter is clean and functioning properly and the temperature sensors are correctly installed and functioning (this was a problem on Hans' '99). And, don't forget to make sure that your clutch is good and not slipping.

Next, make sure that the fuel management (PC-Pro?) is properly connected and functioning. For instance, all wiring connections are correct (soldered connections are best), plugs are fully seated, and MOST important, the boost/vacuum line is connected and there are no leaks (this has been a problem on more than one occasion).

It's also useful to have a vacuum/boost gauge and a wide-band air-fuel ratio gauge so that you can do preliminary tuning and check out basic operation on your own (before paying extra for dyno time).

If all of the components seem to be functioning correctly, then dyno tuning might improve overall performance. Preparations for dyno-testing include making sure there are no CEL codes, the O2 sensor is working properly, and that all ECU settings are stable. On my '00, I'll drive the car at least 30 miles to stabilize fuel trim and other settings. Lastly, take along up to three gallons of race gas in a spare fuel canister (100-octane in my neighborhood...see why below). Dyno tuning typically required input from someone who knows how to read the performance on the dyno. Here are some starters:

I usually recommend starting by setting the AFR on the rich side (no more than 11.5:1) to reduce the potential for pinging and damaging the engine. The PC-Pro is a little tricky to adjust but once you get the hang of it it's not bad (of course, that's the best time to call Tom :biggrin: ).

I helped Hans tune his '99 FFS Coldside last year and ended up with the plot ( http://forum.miata.net/vb/showthread.php?t=251673 ). This dynojet data seems characteristic of those from other FFS kits that have been posted; however, note that the indicated AFR is reading 0.5-to-one point high because the AFR probe was in the tailpipe (after both catalytic converters). The interesting thing is that the more powerful dyno tests show similar curves and relationships where the only difference seems to be a scale factor. So, for discussion sake, consider Hans' dyno to be illustrative.

First, do a full power run at a "rich" AFR, while carefully listening for pinging - of course, if you hear pinging then abort the run until you find and fix the cause. If no pinging is heard, then you should have a SMOOTH torque and power curve from start to redline, about 7000 RPM (NOTE: jagged power & torque curves are characteristic of pinging, or a slipping clutch).

Next, look at the boost curve - on the FFS Coldside, with 95mm pulley, the psi should hit 6-to-7 PSI immediately (at no more than 2,400-RPM) and smoothly increase to 10-to-11 PSI at redline. If the boost drops off abruptly, then you might be seeing rich fuel quenching or belt slip (unlikely with the auto-tensioner).

Also, look at the AFR, in the absence of boost, the AFR should be stock, around 14.5:1 or less. Once the PC-Pro reads boost, then it will increase fuel according to the settings and the AFR should drop to the "rich" initial setting (discussed earlier) of around 12:1 or less. Rich fuel quenching will occur when the AFR is richer than 10:1 or might exhibit reduced power with higher AFRs.

Once you have a baseline to work from, you can start to increase the AFR to a target value of 12.5:1 across the full range, although I'd recommend no leaner than 11.5:1 above 5000 RPM, just to be safe. The goal is to run the highest AFR you can and still not observe loss of timing (which precedes pinging). If you have pinging at 11.5:1, then you have other problems that these adjustments cannot correct. For example, on Hans' '99, the PC-Pro was adjusted to yield maximum power with the AFR from 13:5:1 down to 13:1 from start to 3000 RPM (green zone), from 13:1 down to 11.5:1 from 3000-5000 RPM (yellow zone), and around 11.5:1 from 5000-7000 RPM. The rate of power increase (slope) leveled off above 5500 RPM and no adjustment affected it so that was the best we could do (interpreted as a octane limitation).

Now a double-check - add the race-gas to the remaining fuel in the tank to yield a 30% race gas mix, roughly 96-octane, and do a couple more pulls. If it behaves like Hans' car, the power curves will overlap through the low- and mid-range but should continue to climb where the "pump-gas" curves previously leveled off. On Hans' car, the difference from 5500-7000 RPM was almost five horsepower. This was interpreted as reflecting loss of timing advance due to the lower-octane pump gas.

GOOD LUCK!!!


DISCLAIMER: These are just guidelines and suggestions and may or may not work for you. They illustrate how I would inspect, test, and perform minor adjustments, assuming that the basic setup is good and without fault. I can accept no responsibility for your or other's actions without professional and experienced input.

[Tom @ Fast Forward]

Detonation can occur for a miriad of reasons. 12:1 is a good number but even down to 11:1 (richer) is OK. As a good tuner will tell you, add fuel until you start to lose HP and then stop adding. Rich is good and lean (13:1) is bad.

You are mixing fuel and boost. You want to richen the fuel to 11:1. Your boost should be about 10PSI. That is determined by the pulley ratio.

What we need is a graph like the other one with the Air-Fuel data on it as well as the HP and Torque. Boost would be nice but is not important.


The tuner does not have one graph that shows both boost and AFR, which I thought was real strange.

As to the AFR I thought that 12:1 was the max before detonation could occur. Or am I mixing that up with lbs boost?

When I talked to Tom sometime ago I was real worried about losing another engine to detonation. Tom suggested that by cutting the boost back to 11:1 that I would realize about 175 whp. Since I am getting a timing card, I am not so worried. However, I am going to keep the boost between 11 to 11.5

Most everything you are talking about is way beyond me. However, I have found another shop that has a dyno. So when I go there next week I will take your comments. As always Tom is around any questions day or night.

If you have any more info or comments, based upon the info I have given you I sure would appreciate hearing from you.

[Race Grandpa I]

Thanks for everyone's help.

It will be going on the dyno next Thursday. And no fear of :nuke:

then to the track on Saturday. :scooter:

I will post my dyno charts the following day. :dots:

I am very positive that with your help and this shop's reputation that everything will work great.
:cheers2: