First Hallo, new here on OSO, from SWEDEN.
History:2005 Baja Outlaw 23 with merc 496, org 375hp.
Two years ago it went to a HO with CMI headders and it run great, as usely i want more so last winter it got a 3.3 Whipple SC on top of it an the problem starts.
2800rpm it starts missing on four cylinders and it always the same one (change plugs,wires,coils etc.) and also the tach is jumping down everytime it misses.
NO alarm!
PCM right now with Dustin for the 3rd time.
Tested different PCM with same result.
Changed the crank sensor and the problem went to 4500rpm!!
At the end of season itīs around 4800rpm,strange!
Its possible to get throu the missing area and reach over 5000rpm but no fun.
Anyway a lots of boating with problem.
This season i really got to find the issius

Can mension i got from 23" Fusion4 to 28", now the fun begins
Loking around on the internet and i cant find any similar problem anywhere.
[YOUTUBE][http://www.youtube.com/watch?v=-FojC...=plcp/YOUTUBE]
[YOUTUBE][http://www.youtube.com/watch?v=-R9Pz...=plcp/YOUTUBE]

I see you are checking everything to do with spark, ign and timing....what about fuel?

Scary to think you might have a lean area in your band, with boost and cast pistons it won't last long if that is the case.

The fact that your problem moved from one RPM to another can also mean a fuel starvation issue, was it warmer out when it started reaching 4500 rpm?

Has your current engine been apart while doing the Whipple supercharger? We have seen a damaged reluctor tooth on the reluctors do similar things.

Also, might seem like a silly question, but are you reving the engine in neutral for an rpm max. test, as the ECM will not allow that.

Have you scanned or measured your raw water pressure at those rpms or times to see if it is to low at that rpm. Try disconnecting the raw water pressure sensor on the power steering cooler, ignition key on only and see if the Guardian system alarms.

Which PCM are you using that was supplied with the Whipple kit? Is it the stock Merc PCM555 or a Mefi unit?

Have you run a scanner on the engine when it is doing this as this will show whether the power level is remaining at 100% on the scanner as it should, or it may show the power level droping by a percentage indicating that a fault or snsor may be dropping out at that rpm?

This sounds like the ECM is dropping cylinders as it does when it is in a reduced power level from a actual fault or electrical issue. Remember faults can clear themselves at certain rpms and show up at different rpms while running.

Best Regards,
Ray @ Raylar

Hallo Ray
Try to answer as god as I can.
Motor has not been apart.

No high rpms in neutral.

Raw water is between 30-42 psi, the strange is that it newer goos down to zero, even when motor is off, also change sender-same numbers.
And yeas it make alarms if i lose connection.

PCM555, my own and one from Whipple, One only HO version and one mag verion-same issue....

Scanner done-100% power and no alarm what so ever.

Thanks, Mikael

Fuel pressur is ok...

The water pressure reading you are getting is a reset default (non-moving) one set by Whipple with the previous reprogramming. Your ecm is not really seeing the actual raw water pressure and it may be low due to pump wear issues, etc. My guess is that your raw water pump is really not putting out the required water pressure at those rpms and that you may be having the exhaust manifold coolant temperature sensors reading a temp that is just going above the maximum operation range for those rpms at the ECM. Try measuring your water pressure at those actual rpms. also see what the EMCT sensor temperatures are reading when engine starts pulling back and starts cutting out at those rpms.

Best Regards,
Ray @ Raylar

As we've mentioned before, we feel its a reluctor problem. We tried to increase the filtering of the crank signal, but it only marginally helped. Between the crank signal filtering and new crank sensor, its gone to 4500rpm. To get further, we have to try and filter the signal even more, or the motor needs to come apart and fix the reluctor which is by far the better way.

The motor does not have a lean spot, when the crank and cam don't sync, you get an encoder error and the computer doesn't know what cylinder to fire. The reluctor is either not on straghit or is damaged. Power reduction is NOT coming on when missing.

Its not water psi related, the spare PCM that was sent does not have the sea pump circuit on so it defaults to 43.5psi.

I have a small camera, like a snake. Iīll try, if it goes in to the hole for the crank sencor, maybe I can see the
reluctor and if its looks ok,

I got an idé, under the HO conversion I noticed that the camchain was very slack and I asked an Mercruisershop on this but he told me itīs the way they are... ok so I reused it.

Now it hits me that this could be the problem do I hear a metallic noice in front of engine at idle.
It goes away when I give some throttle.
I meen that ignition is need this cam signal to be accurate with crank signal and when they are slightly away from eachother it will miss ignition signal, itīs always on the same five cylinders thats are after eachother in the firing order, always on cyl. 8,7,2,6,5

What do you say, am I on to something??? Time to take out the engine to change the camchain.

Where do I get hold of an aftermarket chain and sprocket that fits and are tighter than the original one??

Thanks, Mikael

Mikael:

You are now saying that you had a metalic clicking noise coming from the front of the engine?
The stock timing chains on 496 (8.1L) engines built in the GM plant in Tonawanda all had looser than most engine timing chains and it was more noticable in the double roller marine HD chains. This was I have been told due to the robotic installation of the front of the engine and its timing gears and chains and that GM designed the gear with a few thousandths extra smaller diameter to remove the tension on the chain during GM assembly. We have seen this on every 496 we have ever worked on and it has not ever been a problem as far as camshaft timing or noise. If if you install a new chain you will find nearly the same slop in the chain. For this reason I don't think your timing chain and gears are the issue unless they are damaged or improperly installed.
The camshaft sensor is just a simple on-off Hall effect sensor reading a 180 reluctor degree grove in the camshaft gear face. The location of the leading front edge and rear edge of that groove that tells the ECM when cylinders 1 and 6 are at their compression or exhaust TDC. This tells the ECM when the number 1 cylinder is at its compression point for firing and allows the ECM to locate #1 TDC quicker for quicker starts.
If the camshaft sensor circut is not operating properly the ECM will set a camshaft sensor fault code and the engine will either not start or start only after a lot of cranking and the engine will stay in a reduced power mode, not 100% power.
I suspect the metalic noise you describe may be from something else and that if it is big enough it could be setting off the knock sensor which retards timing, limits power and puts the Merc ECM into a reduced power mode.

If you have a scan tool, what is the ECM history file showing on some of these issues?

It sounds like you are saying that you did a camshaft change in this engine to convert it from a Mag to an HO engine?

Did the engine have this problem before you did the HO conversion? If it did not ,then I suspect the crankshaft reluctor was good then and after a camshaft only change the reluctor should still be undamaged or non-defective unless it was exposed to some other potential damage.

I would suggest a mechanics stethoscope with a metal tube to help pinpoint noises on or in the engine.

Try and locate your described engine noise as it may be affecting knock sensors. Also check for an exhaust header or manifold leak at the head to exhaust gaskets as these can sometimes sound almost metalic or like a knocking noise.

Since you have the Whipple supercharger you should also check the belt, lower pulley, tensioner and drive area of the supercharger to make sure you don't have a problem and noise there.

I hope when we get all the input facts and conditions sorted out so you can pinpoint your problem and get it repaired.

Its obviously winter in Sweden, so can you run the engine in the boat out of the water for some of these type of checks?

Best Regards,
Ray @ Raylar