I have a 95 1.8, still N/A running stock ECU/spark/fuel.

I reinstalled the engine about a week ago and have been driving it around just a little bit. It is having some pretty noticeable hesitation between 3000 and 4500 RPMs. Before and after that rev range it pulls solid and normally, but feels starved in between.

I have a NBO2 gauge installed by the PO, and it reads fairly lean while it's lacking power. I don't know how much to believe a narrow band sensor though...

Before I pulled the engine for oil leak fixing (no more leaks by the way) it was running fine.

My first thought was timing, but I am seeing about 11*-12* btdc which I think is ok. My next thought is a fuel filter. I'll probably replace the fuel filter anyways, but thought it would be something else because it didn't hesitate before. It was only out of commission for about 3 weeks, and I put brand new gas in it as soon as it was back on the road.

Anyone else have any other ideas or things I should check? I'll also be replacing the plugs. They don't look too bad, but I don't know when they were replaced and they are cheap and easy.

I'm trying to get it running great before I install the MS and compound the difficulty in trouble shooting. Any help appreciated.

 

Here is a quick video clip of the tach and NBO2 gauge in 2nd gear at WOT. There's definitely a correlation between the O2 readings and loss of power. Every time the gauge dips to the lean side there is a noticeable loss in power. I would assume at WOT that the stock ECU would have that thing pegged on the rich side, but that's not what is happening.

Just before the video was shot I put in new NGKs and a fuel filter. I haven't tested the fuel pressure yet, but can't see why it would suddenly be low. If I can't find a solution really soon I'm just going to put in the 460 injectors, LC-1 and MS so I can at least better diagnose the issue.

 

I found your problem. now fix it.

 

LOL - Thanks Brain. I only pointed that out because I wasn't sure how much to trust a narrow band sensor. Still... the symptom is the lean fuel and power loss. Still looking for the problem.