280 W/ 260 Electronics Problems....help!

[JustMercMe]

Ok guys I'm to the point I wanna set fire to this thing. Heres the problem. I've got a deffinate skip or miss in between 3 and 4 grand. After that range it seems fine but past 7500 the EGT's skyrocket. Thus meaning lean condition right? I'm running an A48 box set on 101 with an SVS. Block is a 280 with exhaust chest and port work done by Ruck.

What I have changed so far:

1. Switched A48 boxes

2. New plugs

3. New fuel pump

4. New water seperator

5. New stator

6. New reeds


What am I missing here? The skip or miss gets worse the longer I run it or the hotter it gets. Electrical wise the only thing I haven't changed are the wires, trigger, and coils. Need some help guys! Thanks in advance.

[us1]

Cracked coil, switch box low speed circuit or water internal leak.

[captcarb]

It's been a few years, but I ran an A-48 on a 260 SVS that needed to be set at 107% to stay below 1175 EGT. It was a gold SVS, they have a weak vacuum signal and need the higher setting. I would start with 110% which should be rich enough to be down on power. Lean it out 1% at a time until the power comes back. That should be a good lake running point with no mid range lean spot. It you are drag racing it might have slightly more power a little leaner.

The best solution is a Brucato box.

Jim

[JustMercMe]

us1 - I'll check the coils next. Changed switch boxes with no change in the problem.

captcarb - Before I rebuilt the engine the box was set on 103 running real rich. We set it back to 101 to lean it a lil. I have been adjusting the vacumn "t" nozzle on top of the SVS to see if that may be it but no change yet.

Thanks again guys!:D

[us1]

Check for a water leak too, I have had a few motor with that exact problem that had internal leaks.

[captcarb]

What rpm was it rich at 103, and how many turns open on the needle valve?

Jim

[JustMercMe]

Talked with Tony Brucato and he told me to start with the valve at 2 1/2 turns out and adjust from there a half turn at the time. I've got it set at a half turn out from that being 3 turns out. At 103 it was running really rich at the lower RPM's.

[captcarb]

If it is not a water problem like John thinks, you could try setting the box richer and get rid of the richness at the lower rpms by screwing in the needle valve. The high temps at the higher rpms means the box needs to be richer.

There is a good chance that the curve in the A-48 will not suit your motor. I have tried the A-48, A-63, Rapairs A-63 clone, several Rapair SVS chips, A-6, and an A-13 on my SVS 260. The A-13 was designed to run with the SVS, has a lot leaner low end, and runs pretty well on my motor. All of the others had some sort of problem in the lower rpm ranges when set rich enough for high rpm with the SVS. The problem can be helped by tuning the needle valve.

The best solution by far is one of tony's PCU's. The whole intent of his design is to eliminate problems like you are having. I bought the A-13 because his PCU was not yet available. I will probably sell the A-13 and go with a PCU when I get my boat going again.

Jim

[stvhelm]

just an idea here that I thought about trying myself. since the svs reduces the volume of the vacuum that the ecu needs to read. couldnt you just add a small air tank to regulate the vacuum? im sure with each revolution of the motor the vacuum changes drastically with the svs because of the small air space. with a plentum the vacuum is much more consistent because of the large air space. just a thought. also the newer svs's are drilled for vacuum all the way through so it pulls vacuum off all 6 cylinders and not just the top one like on the older gold unit with the T fitting on top. Another thing i may try is adding the 1" spacer plate behind the svs and removing all the stacks to keep the same intake length. that will also help increase the air space behind the slide plate to help regulate the vacuum better. The ecu will perform much better with a smoother vacuum reading.

[PhastBoat]

What about lenghtening the vacuum tube to the ECU, to create more volume????

[stvhelm]

I would think the extra volume of air space needed for vacuum has to be before the pinhole fitting the ecu tube gets connected to. extending the tube might just delay reaction times. if a small air tank is used then the pinhole fitting would need to be relocated to the tank and a larger diameter fitting/tube connected from the tank back to the svs. like i said these are just some ideas i'd like to play with. increasing the vacuum space should smooth out the vacuum changes and the ecu can get a better reading.
Also i just wanted to add that this probably has nothing to do with the problems mercme is having I just threw my 2 cents in about the svs and ecu adjusting

[PhastBoat]

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=152717&prmenbr=361

[JustMercMe]

Thanks for the replies guys. I'm gonna try the coils for the skip. The box was set at 103 and running fine within the EGT ranges before rebuild.....Might try going up some on the box see if it helps.....

Thanks again:D

[JustMercMe]

Just to keep you up to date.....

Changed the coils out....no difference.

Think I have the vacumn problem solved. Still missing in that RPM range. Just changed the trigger and going to try that. If no change the only other thing is the wiring harness and new plug wires(old ones have been checked thouroughly and cleaned).:(

[Hot Shot Merc]

ve you checked your Tuner?It may have dropped into the mid or broke.Sometimes they will break off completely and other times they might break off part of it.This would make your motor run bad.Just a thought.:)

[steve]

A vacuum plenum is needed .
The best & easiest solution is to drill 2 long holes behind the slide from top to bottom , like the Merc SVS has and cap both ends. this connects the 6 openings together at idle and smooths out the pulse problem going to the MAP sensor. It makes for a larger volume behind the slide and much crisper low end when you stab it. You will also drill several holes on the Stbd side and install fittings and T them together. THis gives the motor an actual plenum. Thats why Merc's blue SVS doesn't need the valve and has higher vacuum. Ask Tony, he can tell you how to mod the gold version SVS but he cannot do it for you . You may or may not like the pinhole fitting with the new setup.
Wayne Taylor adds a plenum to his MAD units and the Merc carb intakes do it as well although not to the same extent. Give Tony B. a call.......... :cool:

PS: We have also been finding a bunch of the coil ground wires to cause problems lately. They have to ground thru unsoldered wires, thru a corroded casting and thru Loctite (divider bolts). Try making your own ground wires and star ground them all back to the large battery cable on the starter. Eliminates RF and makes for a much cleaner ground. #10 ring connectors And a large ring connector on the starter post, #12-16 wire. Solder them! Another problem was the older Merc harness with the sleeve over the green coil wires ( they should have used mesh or nothing at all) . It can get moisture inside and cause the coil wires to crossfire ( they are at several hundred volts).
If you need to try some other blue coil wires let me know. We have about 30 good used ones sitting here plus a brand new set.:cool:

[stvhelm]

I had a bad trigger once. the motor started and ran fine for the first five minutes then it would drop cylinders. it drove me nuts cause I had to put the boat in the water and run it a while before the problem would show up. as usual it was the last thing I changed:rolleyes:

[sosmerc]

Yup, I agree witih Steve above.....the green wires from switchboxes to coils get overlooked, as well as the actual terminals at either end. It doesn't take much moisture around these wire or terminals to start causing problems. Saltwater magnifies the problem. A few extra ground wires on components isn't a bad idea either.

[JustMercMe]

Sounds like my problem in a way......been acting like it was dropping cylinders at low RPM's but I have been thinking it was fuel related....checking out the new trigger today.

I'll check the wires fellas....thanks for all your help...

[ALLAN DENNIS]

Try changing the pressure Regulator ..had a similar problem with a motor this weekend and changed everything but the Reg.. As a last ditch effort this was changed and Wow ..she took off..
cheers