Hey there all,

My 98 ITR has started acting up on me and I'm having some trouble getting to the bottom of it. This is a fully built engine with Skunk2 Pro1 cams and all the supporting goodies. Engine has run strong for 40k miles.

Symptoms:
- above 3,000RPM and > 30% throttle the engine will stumble, hesitate, cough, etc.
- occasionally feel some hesitation at light throttle tip in.
- engine idles normally.
- engine sounds normal at idle and when cruising around.
- fuel consumption seems a little higher now.

What I've done so far (after symptoms started):
- replace O2 sensor
- replace distributor
- checked plugs and high tension wires. Looked inside the plug holes and top of pistons look fine.
- refreshed my S300.
- checked hoses and sensor plugs...

What I haven't done yet
- data logged the car while running to see if the S300 might see the issue (plan to do that later today).
- take the valve cover off and see how things look under there.

Any thoughts on what I should look at next would be greatly appreciated.

Thanks,
Doug

 

Could it be your fuel injectors or fuel pump?

 

Don't know yet, when I do the data log tonight I expect that will show up in the O2 readings. Thanks for the suggestion.

Doug

 

 

Hey Doug, long time no see! Id say possibly that you need to check fuel pressure, possibly plugged/plugging up fuel filter. also what is your distributor timing set up at? also check your cam gears that you didn't have one come loose and change timing on you. I deal with the those pro 1 cams all the time at my shop either setting up the degreeing on them for installation and maintaining them, or problem solving runnabitly issues. Also check your valve lash, since those are such high lift and duration they may need to be adjusted a tad. just curious on what temp range plugs are you running? are you running NGK Iridiums or copper?

Hope all is well with you!

Chris
R-Tuned Motorsports

 

Any luck? I hesitate to stick my nose in when you've already thrown a bunch of parts at it, and spent a lot of time poking around. But for what it's worth, here's what I think. One essential piece of evidence is that the car ran fine for 40k miles. So, unless you recently made a significant change, then the problem is related to wear. And since you have already investigated the ignition-related wear parts, then you have air and fuel systems left to look at. The symptoms you describe suggest load-related starvation of fuel or air. As others have suggested, you might have a clogged fuel filter or partially clogged injector. Or your air filter might be clogged -- or some other blockage of the air path.

The air path is easy to eliminate as a source of the problem: remove the snorkel and make a quick run. If the problem goes away, you found it. Otherwise, it must be fuel.

I once had a car with similar symptoms. It drove me mad trying to find the problem. Finally, I found that there was contamination in the gas tank that created a clear gel-like substance which flowed through the fuel lines and piled up on the input screen to the fuel pump. At low speeds the car ran fine, but under load, the gel would cut off flow, and the engine would surge. I flushed the tank and lines and the problem was solved. But first I spent a lot of money on parts that I didn't need to replace.

Good luck, Cap

 

I'm sorry to hear you're having issues. Hopefully you'll get it sorted out! Did you replace the distributor with an OEM one?

 

Thanks all for the feedback and help with this!

Have a few more items on my shopping list to install this weekend:
- New fuel injectors
- New plugs and wires (replacing ones that are only 6 months old)
- New fuel filter

I've also:
- Cleaned all the contacts on the engine bay connectors and ECU.

@Chris, Thanks for the suggestions! I'm gong to take the valve cover off this weekend and check for things under there, I'll also check the gears as well to see if something may have slipped. I'm running NGK PFR7G-11 plugs. They are a platinum plug that I've been running for nearly 10 years now on this build.

@TypeRod, I didn't order a new OE distributor as they are no longer available. I did find a new one that was well reviewed and felt very solid when I installed it.

@DrCap, I'll check my air filter and TB this weekend and look for any blockages. If after all I've done this weekend doesn't fix things I'll open up the fuel tank and have a look.