GT40 (1997) Running Rough /specific

[FMSKI]

OK water testing the new resto and this engine hasn't run in 1 year. EECIV of course, and I think it's a quality system for its day!

Symptoms:
Vibration at idle and puttering around.
Moving onto plane, rough/chugging feel at 800-1200 RPM. This is the worst zone
After 1200-2500 not too bad, still a miss or two.
2500+ sustained running I can feel drop-offs. Enough that I don't want to ski it.
I can go WOT, will get to about 65 Kph-ish but still having those dead spots, (feels like a slalom skier pulling on the boat for 2 secs at at time).

Boy I miss that solid power!

History:
1. Didn't start in July so changed the FCC filter found a lot of rust and pump had jammed. Cleaned it all up, new filter unjammed the pump and looks OK
2. Fuel pressure is around 35 PSI, peaks at 40 PSI when throttle is cracked. Running around the lake, pressure is stable say 32-36
3. ECT ACT Sensors are OK. Power seems to be good to relays etc.
4. Had an air leak at the idle control solenoid, fixed that & running a bit better.

NO codes, reader returns an 11 all systems good. Distributor cap, rotor, plugs, wires are recent/ new.
The distributor bowl is pretty rusty so cleaned that up but no change in operation whatsoever.

Usually I am pretty good at these things, but this one has me a bit stumped.
Leaning toward fuel (injectors?) but can be convinced to try otherwise.

The engine did bog/recover sometimes when hitting it with a skier for the past few years. This was a bad thing for beginners.

thx,

[FMSKI]

So after sleeping on it, I'm pretty sure it's the distributor. Behaviour is too switch-on consistent to be fuel. Started up this morning and watched the tacho and sure enough at every stumble the tach needle drops rpm, like jumpy-quickly, way too quick to be mechanical. Therefore looks like the signal dropped out for that split second. So distributor on order from Ebay.


PS:
90's VW had a problem with crankshaft sensors, if hot would lose its signal = no start. You could see this by loss of tach rpm. Came up wtih a work around to pour ice water onto the sensor, boom she'd fire. Once running it would keep so.

So one HOT summer day my son's friend Golf had no start at our place. I say "get me a torch (flashlight) I'm going to the freezer". Drained my cup of ice water onto the bell housing. "OK give it a try" Fires right up... amazed dub teens.

[Jonny Quest]

At the end of last year, I changed out the distributor cap and rotors (brass terminals). Then a few weeks ago, I just changed out the FCC filter, fuel pressure regulator, and all 8 injectors on my 2001 GT40. I had the "loping idle" problem too, so I changed out the MAP and Idle Air Control. The engine is running like a dream now.

JQ

[FMSKI]

I replaced the MAP sensor and wow, in the zones the distributor signal is OK, the engine is super turbine-smooth. Back to how I remember it to be when new! Pretty cool.

Since there is no MAF, the MAP sensor is pretty critical for A/F mixture. eg - If you pull the vac line from the sensor the engine immediately dies. A/F mixture is essentially a function of the MAP, ECT and ACT. MAP is a cheap part too - $100 or so.

On current engines there is a MAF with O2 sensors doing the trimming. Might have mentioned that before.

[FMSKI]

New distributor arrived today and installed. Problem solved, engine is operating without a hitch over all rev ranges.

I marked everything on the old distributor and got the new one to line up with 1/8" after the rotor shaft kinda rotates down and in.

Started it up and the idle was super smooth but exhaust had a bark to it, so I figured I was timed too retarded. Did a quick test run but 60Km/h was tops and clearly no advance happening.

Got out the timing light and I was running almost -10 deg (ATDC) little SPOUT plug removed.

Rotated the distributor but hit the limit at 0 deg or TDC. So had to pull the distributor, reposition the rotor, then rotate the base back quite a bit.

Plenty of range now & set timing at 5 Deg BTDC but done that at (idle) 700 rpm.

Will check it tomorrow at 2000 rpm (at least that is what is called for in manual)