Issues with GT40 1997 after shop service was performed.

[97MastersEdition]

1997 SN 196 GT40

Long standing symptom/problem prier to and reason for servicing engine last week:

Running warm up to 190 at idle after a few slalom passes. But in the pass would go down to 170s. Then climbing back to 190-5 after dropping skier and lining up for another pass. Back down during pass. Been like that for a while. Did all the usual; new thermostat and gasket, checked all hoses, checked trans cooler, checked all ports in thermostat housing, checked intake under hull and so on. All good. Conclusion; flow problem due to old manifolds (1100hrs). Plus old hull huger muffler was going bad..developed a crack.

Other than temp issues and some needed maintenance, the boat ran smooth as butter. Strong, responsive and sounded normal.

Sent to shop week ago and the following was done. The shop replaced manifolds and risers, plus some items added to the job for general maintenance. Specifics;

1. New Exhaust manifolds, risers, gaskets and ss fasteners (old ones were in fact bad.. I saw the inside of one of them)
2. New Hull hugger muffler
3. New exhaust hoses
4. Replaced fuel filter-FCC filter
5. Installed a new inline fuel filter. It did not have one before.
6. New thermostat/gasket
7. Oil change and filter
8. Transmission fluid changed
9. New cap and rotor
10. Cleaned flame arrester
11. Tank drained and 5 gal of fresh mid grade added. Shop chose to do this but gas in tank was not more then 2 weeks old and had full can of Seafoam added
12. Clean and grease rudder and rudder port
13. Shaft packing
14. Bilge cleaned

Received boat back. Started and idled normal. Backed off of trailer. Short 100yrd run to dock done at idle speed; felt and sounded normal. Parked boat. Few hours later did a test ride. Seemed ok at first. Seemed to run as normal throughout power range and idle. But within a few minutes, idle started stuttering. The range between 1000-2000 as throttle was pushed up, it stuttered and struggled a great deal. Continue pushing throttle and at 2500rpms, it gave a mostly normal response on up to WOT. Some slight stutters detected but barely noticeable compared to the 1000-2000 range. Back down to 1200 still in gear, the boat started surging between 1500 and 2000. Up and down, up and down. Continued this until the throttle was repositioned. Idle still stuttering. Left boat sit for a couple hours, then second test ride. Seemed to run slightly better this time out but was repeating all of the same above symptoms after running for a bit.

Day 2, added 10 more gal of mid grade gas and test ride results were exactly same. Cold it ran well until reaching normal temp. Then same poor results.

At PCM’s suggestion, the following has been attempted or found to be normal when checked. After some but not all, a test ride was done with the exact same symptoms as above..no better, no worse.

1. Removed new in line fuel filter, as it was not part of the system before. (test ride..no change)
2. Both HP and LP pumps prime as normal with key turn. Aprox 3 seconds
3. LP pump tested with normal flow/volume (20oz in 10 sec) and pressure. All connections appeared normal and were reseated. (test ride..no change)
4. Fuel pressure gauge shows 35psi at idle and 41psi at WOT. No change during lake testing for both points. Also, fuel pressure held with key off @35psi.
5. FCC opened and full of fuel to the top. No water. All connections appeared normal, reassembled and psi did show again as normal with gauge at idle and WOT. (test ride..no change)
6. At idle removed vacuum hose from Fuel Pressure Reg on rail. PSI jumps to 41psi 830rpm when vacuum hose removed. Reattached hose and normal operations of psi at idle-35psi 730rpm and 41psi at WOT. (test ride..no change)

All symptoms have stayed exactly the same for every test ride. Over several days of lake testing it seems that the issue arises when boat is up to temperature (160). Seems there are no issue when runing from a cold start and running up through the power band. 100% normal operation. Smooth as butter. Once boat is at temp, the issues at idle (stuttering) and between 1000 and 2000rms (struggling, running rough, losing power) are present. At 2500rpms it catches and runs close to if not normal through WOT.

Thinking sensor problem possibly temp sensor as it only runs poorly at temp. Or throttle position sensor as it runs the worst between 1000-2000rpms. But do not know how to test any of these. Not sure what other sensor it could be but the symptoms/problems are very very consistent. Cannot think of anything else it could be.

The boat ran fine before entering the shop and poorly after. The shop did not lake test boat before repairs and Im confident they did not hose test it. Problem described to them was running warm and a few maintenance items needed so perhaps no need to. I would have had them address poor running if it was doing any of it prior. They contend that it must have been running poorly before their work. It could be a complete coincidence and a separate isolated incident. Or maybe its something/parameter that they changed that is causing the computer to not properly calculate fuel needs. But just guessing. Perhaps something was bumped. Truly appreciate any help.

[ski4evr]

Replace your distributor cap. I put a new one on before a vacation, and ran terribly all week. eventually put another one on and fixed the problem. It started crossfiring before the wife backed out of marina. spent a week on vacation trouble shooting everything but the cap. Possible that the plug wires were damaged when changing cap? Always look for the simple first.

[kend]

Too much timing advance can make it run hot; maybe do a test at different RPM to see how it's advancing