Help, Please. '95 Miata, stumble under a load up to 4000 then it takes off.

The car is running a fresh motor with less than 1000 miles. The issue is a stumble, under a load, that starts to build from 3200ish rpm and at 4000, and beyond, goes away. This is an OBD-I car that the "Check Engine" light does go on, some times, but then goes out again when you are driving under light loads.

For the cost of a valve cover gasket the engine builder did confirm the cam timing was correct.

This morning the Cat was tested, for pressure( 4 and 2 ) and passed. I did swap the EGR, the new "used one" is working much better than my old " 151K " one. The old one acted like a vacuum leak to 4000 and when the EGR shut off it was like a light switch. The motor then runs great and pulls strong.

During the engine build the fuel injectors were blue-printed. I am picking up a fresh set of NGK Blue wires tonight. The fuel filter is fresh.

I do own an E36 and have been down the replace everything to fix-it path, just checking the hive to add to my resources. I wish I had the room to keep a running spare that could act as my test stand, for these dam sensors. But, I really like staying married, for over 30 years. So far.

Ignition timing? You should be able to at least check quickly with a timing light.

Robbie wrote: Ignition timing? You should be able to at least check quickly with a timing light.

Note: there's some connection that needs to be jumpered when checking ignition timing.

Thank you, that was confirmed as in spec by the engine builder. But, we are going to swap a know working Crank Sensor this week end and re-check the timing.

Yes, the hair pin was in place.

What's the stored code?

Keith,

They disconnected the battery when they worked, testing the cat, this morning. Next time it pops the check engine light I will post the code.

David

If you have an OBD2 scanner that supports live monitors it might be worth a few minutes to drive and watch the O2 sensor.

I had a pretty annoying acceleration issue on my 97 below 4000 rpm that turned out to be a bad O2 sensor (always reading full lean) that got ignored in open loop.

It's not an OBD2 car, so a scanner won't get you anywhere. You retrieve the codes with a paperclip.

Sorry about that, I did not really know when OBD2 started on the Miata. Lots of other cars changed over in '95 but I guess Mazda didn't.