97 GT40 surging, running bad and not reaching max RPM

[skihartwell]

This engine has been awesome up to 750 hours! In respect to the engine, it may be the owners lack of proper care. Anyway, I changed the plugs, the fuel filter(cannister type) and the cap and rotor this week. I ordered new plug wires but the dealer forgot to send them. I Put some heat in the fuel as I suspected at first water, but the RPM's surge up and down and it appears more like electrical. Often times the oil pressure guage surges and pegs all the way to the right and then all of a sudden it will come back to normal. At first, a few weeks ago the engine was just missing a litte at WOT. That cleared out and then it started running rough at surfing RPM around 1200 RPM. Now it's running rough up and down the slope and just getting worse. Before I take it to a shop to sit for several weeks, I'd like to hear some suggestions.

Thanks for any help.

[M3Fan]

RE: 97 GT40 surging, running bad and not reaching max RPM

Here's some easy stuff- Might want to make sure the fuse at the battery is good and clean. This is a 10AWG or so wire that is on the positive side of the battery. Maybe if the connection was flaky it would appear to miss a bit, who knows. If it's rough at idle, you might consider cleaning out the idle control valve on the side of the throttle body, as well as the flame arrestor on the intake. I'm no mechanic but just some easy stuff to check out I suppose.

[ToolBoy]

RE: 97 GT40 surging, running bad and not reaching max RPM

You may need to check all of the little screens along the fuel line. There are a couple at the tank, and one at the low pressure pump. Pull and check all of your connections to the fuel pumps. check the fuel pump and ignition relays and the connections. Could also be your low pressure fuel pump. If fuel injected, check your fuel pressure on the injector rail. It is a schrader type valve. It should be a steady 40 psi. If it is dropping up and down, it is likely a fuel problem

[skihartwell]

RE: 97 GT40 surging, running bad and not reaching max RPM

Thanks for the replies. Where is the low pressure fuel pump located? I will check the efi fuel pump pressure but I need to pick up a guage. Also, what spark plugs are being used for the GT40? Any better than others?

[ToolBoy]

RE: 97 GT40 surging, running bad and not reaching max RPM

Gauge is about 40.00 at Auto Parts shop. Low pressure fuel pump is the first device your fuel line comes into. Location varies with model. It is cylindrical and the size of a coffee mug. Not sure on plugs. Doesn't sound like a plug problem.

Not sure what the oil pressure gauge going far right means. I read on these forums the oil pressure sensor and water temp sensors going whacky, and putting the engine into pre-programmed trouble modes. That it is not going to full RPM means in might be slipping into Limp or other modes to protect the engine based on what the sensor may be (even falsely) saying to the electronic package.

Check other GT-40 trheads on this site, and you will find some trouble shooting methods for sensor issues. These are simple checks. Another fella on this site had all of his trouble trace back to a corroded in-line fuse on the battery cable in the battery compartment.

[skihartwell]

RE: 97 GT40 surging, running bad and not reaching max RPM

After doing most of these things from the above string, I ran the boat again. With the cover up and running about 3000 rpm I hear a quick snapping sound, like electric from the distributor cap. Could this be a plug wire or something inside the cap breaking down? I'm about at the end of my capacity before breaking down and let a pro get aftetr it. Any thoughts???

[Rick]

RE: 97 GT40 surging, running bad and not reaching max RPM

Could be arcing between a pleg wire and ground, or a plug wire unplugged or a bad coil. I would guess that one of the plug wires is pulled out of the cap. It also sounds like a bad ground either at the engine breaker box or battery. I would check these. Does the check engine light ever come on? I would guess not as it sounds like ingintion missing. This may be way off... did you cross 2 of the wires when you plugged them back into the distributor cap? Check the firing order. Good luck

[nms1991]

RE: 97 GT40 surging, running bad and not reaching max RPM

Replace your spark plug wires they are breaking down due to age. Use the right one made by PCM for the GT-40 they are cut to the right length and can be routed the right way to prevent burning the wires if they are routed to close to the hot spot on the manifolds.

[triplered]

One more thought -- there were a bunch of 1996 PCM Gt-40 engines that had a recall on a fuel line found in the fuel control cell. I know yours is a 1997, but it is possible that the fuel line in the FCC has burst which could cause strange performance.

All told, I agree about the spark plug wires (connections). Just thought I would throw out another possibility.