Help, Please. '95 Miata, stumble under a load up to 4000 then it takes off.| Builds and Project Cars forum |

jr02518 Reader
6/21/16 1:19 p.m.

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.

Robbie SuperDork
6/21/16 1:24 p.m.

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

johnnie Reader
6/21/16 1:26 p.m.

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.

jr02518 Reader
6/21/16 1:29 p.m.

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.

jr02518 Reader
6/21/16 1:30 p.m.

Yes, the hair pin was in place.

Keith Tanner MegaDork
6/21/16 2:24 p.m.

What's the stored code?

jr02518 Reader
6/21/16 3:26 p.m.

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

ssswitch HalfDork
6/21/16 4:36 p.m.

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.

Keith Tanner MegaDork
6/21/16 5:26 p.m.

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