2008 back fires through intake under a load

[Willhamm]

I have a 2008 super air 210 with 5.7 343 Excal. Mainly at cruising speed but a little when i punch it. At neutral it operates fine. Problem is it will lag like water in the fuel but will occasionally backfire through the intake. When i punch it, it will take off. It has 150ish psi at 700rpms on test stand, 60psi at fuel rail idle and throttled. I’ve replaced plugs, wires, cap and rotor, both fuel filters. Timing check with Computer. Did realtime read while symptoms exist and no codes. Shut down each cylinder and noticeable change on each. Engine has approximately 90hours on it. Ran fine for a while then progressively got worse.

[Miljack]

Have you cleaned the "air cleaner"/backfire screen on the intake manifold? Those face backwards in that boat and can get clogged up, plus the 210 engine bay is small.

[Willhamm]

Yes. Even removed the spark arrester (air cleaner) and had engine compartment open. But that’s exactly what the symptoms would explain except for the back firing.

[core-rider]

I had a similar issue on my 2003 and it was cap/rotor very corroded (original 19 year old parts), but you said you replaced them.

When you say 150ish psi @ 700rpms are you talking about cylinder compression numbers?

[Willhamm]

Agreed, cap and rotor could cause it but i replaced them and had no change. Yes cylinder compression

[Miljack]

Is the '08 Excal a "fly by wire" throttle setup? Could it be related to the throttle body? Maybe the actuator or the butterfly shaft is a little sticky/slow moving?

[FMSKI]

Doing some searches - some people have replaced the distributor.
Might want to check that full voltage is going to the ignition system (remove and re-seat relay for example)
Here is a tech bulletin I found posted on BOS.


Link would not copy but here it is PCM Service Update PRODUCT INFORMATION UPDATE Updated CAM Retard Specification for 2007-2008 Engines #SUP2009-01 February, 2009

This Product Information Update supercedes SUP2006-04, Information on Setting CAM Retard PCM 5.0L (Pro Ski) and 5.7L (Excalibur) engines, serial number range 470001 through 485993. When rotating the distributor on the affected engine, you are adjusting what is called “CAM Retard.” This parameter represents the position of the distributor rotor relative to the proper terminal in the distributor cap when the spark is delivered. The specification indicated for this engine is 0-4 degrees. If the engine is set at 0 degrees, under certain precise RPM, temperature and load conditions, the engine can “crossfire.” This means the spark jumps to the wrong terminal within the distributor. This can cause a slight backfire or sputtering under this condition. To ensure this condition does not exist, CAM Retard should be set between 6-8 degrees on engines between serial numbers 470001-485993. This is a correction made to the tune-up specifications and should be checked and set to specifi cation during normal service intervals. In most cases, the problem does not exist. This is not an update that requires you to have the customer bring the boat in specifi cally for this update, it can be simply done during normal tune-up and/or commissioning procedures. A new specifi cation decal needs to be installed after the adjustment is made. Contact PCM in order to receive updated specifi cation decals, p/n R143170B-U, which indicates the correct CAM Retard specifi cation. NOTE: Engines built starting with serial number 485994 have been changed to a new specifi cation (15 +/- 2 Degrees) and circuit diagnostics added. These engines DO NOT need to be changed.

In order to properly set the CAM retard, the following scan tool MUST be used: PC Based Diagnostic Software: Diacom Diagnostic Software, Marine Edition, by Rinda Technologies, Inc. Available for purchase through PCM, P/N RT0086. 1. Connect the laptop to the engine’s data link connector. 2. Per the tool instructions, navigate the tool to view ECM data. 3. Find the engine parameter labeled “CAM Retard.”

4. Engine must be running in order to view the CAM Retard value. 5. CAM Retard value MUST be set between 6-8 degrees. If the value is within specifi cations, make sure the distributor hold down bolt is tight. 6. If the value is outside the specifi cations, loosen the distributor hold down bolt and slowly rotate the distributor until a value of 6-8 degrees is achieved. Tighten the hold down bolt securely, making sure the CAM Retard value does not go outside of the specifi cation. Once the distributor hold down is tightened, verify the value still remains between 6-8 degrees. Important: The basic principle that the distributor must be installed into the engine properly still exists. If the proper CAM Retard cannot be achieved, check the installation of the distributor. 7. Clean the surface of the old specifi cation decal and install new specifi cation decal, p/n R143170B-U.

Engines Affected: 2007-2008 5.0L MPI (Pro Sport) ALL S/N: 470001-485993 2007-2008 5.7L MPI (Excalibur) ALL




PS: My 2007 343 is missing or feels like a lag at first run-up start, esp at part throttle. . I sprayed the HT (high tension ) system with silicone lube seems to have improved it . Might see if I can get something hooked up to it (diacom)

[Willhamm]

Yes cam retard is set to 6*. We played with different settings while running but no help.
what is the HT system?

[FMSKI]

HT is British for high tension, where tension is voltage. If you spray down the coil, leads, joints, boots etc, also cross the ignition wires.

I ran my boat again today. So I think I figured things out in principle:

Engine or operating heat produces a better electrical connection (eg ground) or function.
The distributor is made from aluminum, the block cast iron. They expand at different rates and also the two different metals can cause corrosion. Distributor ground connection perhaps? Or electronic - something is working properly at temperature, not when cold.

Tomorrow - I'm going to test distributor ground (VOM) engine cold.
Also going to run the engine to temperature just idling at the dock, then go for a boot.
My guess is no missing or lagging.

[Willhamm]

So back at, being its that its that of year. I removed, checked and cleaned all the injectors. Still has the occasional mis at cruising speed. With a soft acceleration it pops through the intake and lags power slightly but if i hammer down, it with take off.
could the issue be in exhaust? Had a similar symptom on a truck with clogged cats.

[teamseal]

inspect the distributor housing where the cap screws onto the housing. seen many times a customer replaced cap and rotor only to have same problems, found the housing had cracked. not a fan of the plastic HVS distributor. I have changed a few out with a stsndard NAPA aluminum Automotive HVS distributor. 1996 chevy tahoe 5.7.. set the cam off set correctly and took care of the problem. do recommend though utilizing the marine pcm cap and rotor on it and not the automotive counterpart.

[SilentSeven]

Odd one.

Not sure this information translates to the PCM 343...but it might. My GT-40 had ignition issues (occasional miss mostly, no backfire) that was associated with a flakey hall sensor in the distributor. If not familiar, the hall sensor is the device in the distributor that triggers the spark. Fix was to replace the distributor. On my GT-40 I was able to locate the factory Ford part number and so I sourced a remanfactured automotive unit at a much lower cost than a PCM unit. On some distributors, you can just replace the sensor.

This might be something to look into.

If you can just swap the sensor, it's likely a pretty low cost item and worth the swap. IIR, a PCM distributor is spendy so you'd likely want to be sure it's the root cause before you go that path. I believe some automotive parts stores can bench test distributors - might be something to look into.

[pauldixon]

could be your fuel injector(s). I had the same issue. However, I could diagnose it by killing the injector for a cylinder at idle. Are you positive there is no change when you kill the injector on each cylinder?

[Willhamm]

That sounds very likely. A new distributor was next on my list of parts to throw at it, but yes, it is quite pricey.
Teamseal, are you saying that year and model distributor will work on the 343 PCM but you would go with the OEM cap and rotor?

pauldixon, i stated i did have a noticeable change in sound and even on the graph on the computer when we shut down each cylinder.

[SilentSeven]

I think teamseal did ID the likely automotive distributor for the car. If it were me, I'd just order one from my local auto parts store and do a side by side comparison. I concur you should use the PCM rotor and cap.

Here's 1996 Tahoe distributor prices at RockAuto. I see a new Delfi unit for < $200 and other options for $55 and up....

Or if you want to try replacing internal parts, looks like "Distributor Pickup Coil" and "Ignition Control Model" (further down on the page) are candidates.

While not a 5.7L engine, here's an interesting vid where a guy does a side by side comparison of a worn out Vortec 4.3L V6 distributor and a new one. Looks similar...might help with the assessment of yours.

https://www.youtube.com/watch?v=trlIADBfhSw