Help me diagnose this problem please!

[Darth G-F]

So the car is katana supercharged. It pulls nicely most of the times. But it happens sometimes that between 7000 and 8000rpm, the power just cut.

What I know:
-Fuel pressure is rock solid at 48psi
-Cam lobes are fine
-The belt doesn't slip (new tensioner and belt installed)

What it could be:
-Faulty bypass
-low compression in some cylinders
-vaccuum leak somewhere...
-Defective m62 unit:

Any idea? Have anyone of yo seen a dyno like this??

[chuck_risen]

If your supercharger has the teflon sealing strips you may possibly have a nick in one.

[Demonized]

Power through the whole band pretty low there...

I'd check for vacuum leaks.

[Darth G-F]

Car pulls much harder than the numbers suggest. Something was up with this dyno.

I'm more concerned about the dips in power after 6000rpm...

[turbophil]

Hi Jeff,

If the dyno is that far off, then I guess it I won't pay any attention to it?????

Start at the basics. MOST problems tend to be VERY simple.

Short of the dielectric grease on the coils you just did, any changes at all to the car that preceded the problem?

Any chance you got a bad tank of fuel?

Have you pulled your spark plugs to have a look at them? They tend to tell all... (be sure to number the coils and plugs)... On a similar note, is there any chance you've got a pinched coil wire on cylinder two or four where the coil cover bolts down to the head?

Have you hooked it up to scan tool yet? You can buy them cheap anymore and they come in handy. I've even got one that allows sensor monitoring on my iphone. Look at spark, airflow, etc... If the car is running this poorly, something will likely be showing up...

Have you checked piddly stuff like the wires for your injectors. Any chance they're shorting out where your splices are? Would probably throw a code if so, but worth checking...

If all else fails, do a leak down. Compression tests will typically only show what spark plugs will tell you, i.e. a blown/dead cylinder. A leak down will tell you MUCH MUCH more and they're not much harder to do...

There's a very remote chance it could be the coupler inside the blower nose... Those have been known to disintegrate and cause really unpredictable problems until they finally completely let loose and just stop working... This would be absolute last thing I would check though...

I doubt it would be the cam lift or phase solenoid. Those little guys are pretty reliable. But I suppose they could be malfunctioning. Again, would be near the bottom of my check list...

Stuff you can all but rule out. Regarding the bypass valve, when they go bad, they tend to stick shut, not open. It's the diaphragm in the valve that tends to take a dive causing the valve to stick shut (it's natural position). In which case, your intake temps go sky high when cruising down the highway, but your WOT power remains the same... so probably not your BP valve... Probably not a vacuum leak. They tend to be a problem at idle, not at WOT. At WOT a tiny air leak is pretty insignificant...At idle, that's not the case.

Given that you've already started the diagnostic part, That's where I would pick up... Good luck!

Phil

[charliex]

compression loss wouldn't cause the dips, its hard to tell since i'm not that used to mustangs, and i don't know if they interpolate or what the sampling rate on the drum is, but the dips look like dropouts, not power, you'd feel a hesitation in the crar with a 50 lbs/ft drop in torque.

same thing with the cam phase/solenoids, it'd throw a code on the offset straight away, on the lifters not straightaway, but the power curve would be way different, they do definitely go wrong i've had three or four cars this month alone with problems in the VVTLi lift/offset.

On a dynojet if you loose RPM it stops drawing everything (which is really annoying!), if you get wheel slip you get erratic drops, these are the problems with roller dynos, so much can go wrong with the inteface between can and dyno. I don't know what a mustang will do.

[Darth G-F]

Thanks Phil and Charlie.

The dyno just shows what the car actually feels like. On the street in 3rd or 4th gear (will certainly do it in 5th or 6th but this would be insanely fast to check on the street) when I pass 7000rpm power do drop. Revs stop rising for a second or two, then boom power kicks back and the revs start to rise again.

1st and 2nd gear I feel no drop in power, but it probably is because the gear is gone so quickly I don't have time to feel it.

Again pay no attention to the power level on the graph car pulls as strong as ever. Just the power drop at 7000rpm...

Can the DBW be the cause??
Can the knock sensor cause something like this??

Here's a pic of the plugs:

[charliex]

What is the gap set too ?

i posted what a knock will do to a dyno on monkey, its much more aggressive on power loss, plus you're unlikely to get knock at 7000 RPM

So which dip do you feel ? the one at 6600 or the very last one around 7500 RPM?

Have you modded the fuel system ?

[Darth G-F]

Fuel system is modded with swirl pot, but the FP is set to 48psi and doesn't move at all from idle to cut off.

The power dip I feel is the one around 7000rpm.

I don't know what happened I went for a ride today with Jean (forum member) and couldn't reproduce the problem, not once...

I did fill it up yesterday, so maybe it was bad gas.

Anyway, we checked the fuel trims and everything is ok. We checked the compression and believe it or not, but I got exactly 224 for every cylinder.

So fuel problem is ruled out. Compression is perfect. No pinched wires. Plugs are ok. Belt not slipping. Power is great.

I couldn't reproduce the problem but the remaining cause is likely to be VVTi related. Unless someone has other ideas?

[Jermaine@VF]

Originally Posted by Darth G-F

Fuel system is modded with swirl pot, but the FP is set to 48psi and doesn't move at all from idle to cut off.

I take it you are running a walbro 255 pump in a swirl pot? If your fuel pressure isn't rolling off like the stock pump, there is your problem or lack of a problem, especially if it wasn't tuned with the swirl pot installed. What did the wideband say while it was on the dyno? Looking at the power I probably say you are in the 10's on the top end.

That's my guess!

P.S. Smell the spark plugs. Smell like fuel?

[turbophil]

J- That's not it.

His plugs are pictured above. While not the best view of the tell tale portion of the plug, if he were choking out that bad, he'd have a wet plug. He has run at least one, and probably more track events with the surge tank and no problems. There's must be about 20-25 cars running around on the streets and track with Jeff's same fuel surge solution and one of Charlie's tune...
Obviously a scan tool would show his trims at low load and he could fine tune the FP with that, but running a static pressure on these cars with standarized tunes has not been a problem in open loop that I've seen....

take care,

Pv

[Jermaine@VF]

It wouldn't hurt to see the results. The scan tool wouldn't show anything especially at idle since the car is running relatively the same as stock fuel pressure.

If fuel pressure isn't falling as he said. Then the tune will definitely be different.

[turbophil]

no doubt. It's just that the problem just showed up and began with a misfire MIL...

Keep in mind the stock system with his type of power idles at what, 46-47 psi or so... Drops to about 42 psi at WOT and redline (remember only a 220 whp car here) and it might be at 44-45 psi at 6600 where his major cut-out problem is.... Granted, he's running the static pressure a touch high (48), but a couple psi variation won't cause the car to hit a wall like it is at 6600 rpm--- especially after it has been running so good for an extended period of time...

The only way I can see his fuel system being a problem is if the gauge is malfunctioning causing him to set the static pressure waaaay out of spec... But then again, I'd think we'd see evidence of that on his plugs...

-PV

[Jermaine@VF]

Wideband o2 reading will tell if my assumptions are correct.

Darth, when did it start?

[turbophil]

Originally Posted by Jermaine@VF

Wideband o2 reading will tell if my assumptions are correct.

Or it will tell you he's misfiring and dumping fuel into the exhaust

[Darth G-F]

Well it all started way before the fuel swirl pot. When I got the car out of storage in spring, I felt the car had some hesitation sometimes. Usually around 7000rpm.

I then had major fuel cuts on the track and used Phil's swirl pot with great success for at least two (if not three) events.

But a couple weeks ago, I felt the hesitation was worst. But I didn't really mind because the car was turning the same lap times it always did and otherwise everything was running very good. I just thought that my cat was starting to give in.

Then on the last track event, first time out, the car bugs worst than before and CEL turn on. P1302.

I checked:
-the cam lobes, ok!
-the cat, ok!
-the plugs, ok!
-coil, severe burn, major arcing! I greased them. CEL disappeared. Never came back.

The car was still bugging at 7000rpm though and I went to the dyno. Nothing really showed up. But we changed the belt tensionner and strap thinking the belt was slipping. Car still bugged on the dyno. Lowered FP to 48psi static. A/F are 10,9 at cut off about 11,2 during the 7000-8000rpm zone. Not bad and pretty safe imho. Certainly not rich enough to cause bugging.

So I went back home wondering. Then Jean (forum member) came home and we checked fuel trims. Everything was perfect. Checked compression, exactly 224psi on all four cylinder!

Went for a drive, nothing. No bug, no hesitation nothing at all.

Problem either cured itself, or it was gas quality related (I had filled the car up prior to Jean showing up).

Keep in mind that winter is just around the corner here. It is possible that they began with the winter additives in the fuel and that it was messing my tune or knocking or something.

Anyway, after at least 10 pulls in 4th gear, I couldn't reproduce the hesitation at all. Car just pulls nicely as it always did. I just don't know what went wrong, but it can be the coil arcing AND bad fuel.

Even though I greased them good, I will probably change the one of the coil that has been physically damaged by the arcing.

Me and Jean exchanged rides and man, does his VF2 feel good! Awesome sound too! It pulls on my katana just enough to make me wonder how freaking fast I'd be on the track with that extra 50whp!!!

[Seb]

I could be totally off here, because I really don't know how the Lotus sensors work with the ECU.

1) Go one step colder on the plugs if you haven't already. Also check the gap, and maybe narrow it a tiny bit. You might be getting spark blowout.

2) I don't know if or how Lotus uses knock sensors. Could it be that you got a crappy tank of fuel and are knocking up top, causing the ECU to retard timing?

3) You have a horrible boost leak, causing the car to run out of fuel on the top end.

4) Your compression numbers could also contribute. A compression tester is $20 from autozone, I suggest doing that.

[Jermaine@VF]

Phil: O2 sensor read oxygen not fuel. If he were misfiring it would show up as a lean condition on the sensor.

Did you change the plugs or just put them back in? Sounds like you had to lower the fuel pressure. to get the fuel back into the 11's. Which is still a full point off from where you want to be. Fouling out a set of plugs can cause misfiring.

[Darth G-F]

Originally Posted by Jermaine@VF

Phil: O2 sensor read oxygen not fuel. If he were misfiring it would show up as a lean condition on the sensor.

Did you change the plugs or just put them back in? Sounds like you had to lower the fuel pressure. to get the fuel back into the 11's. Which is still a full point off from where you want to be. Fouling out a set of plugs can cause misfiring.

Well Jermaine, when I buy the VF2 upgrade, I'll probably replace the faulty coil and all spark plugs at the same time!

Just back from another drive. I did 4-5 pulls from 4000 to cut off in 3rd and 4th gear and again got nothing at all. No hesitation at all. Car just drove perfectly.

How much would a cam lobe job be? Maybe I can trick my gf into thinking the lobes are shot while I secretly put that money on a VF2...

[Jean]

Coil no 3 was arcing for sure on Jeff's car. It might be a good idea to replace it, but dielectric grease is doing its job.
Knock sensor could have been for something too as there were some vibrations from brakets on the engine and I don't know how much that sensor is responsive.
There is no vacuum leaks, no boost leaks, STFT are between -3 and +3 and the compression is the same as a new engine...
Sometimes, s*** does happens... but last weekend his car was running great, pulling right to the red line without any hesitation.