'93 D21 ka24e runs rich after HG change

[Dogfather]

Changed blown head gasket and when reassembled, the engine runs rich and the mileage is about 4 mpg worse. Timing is 10' BTDC, vacuum is 22 " hg, no vacuum leaks that I can find via ear/tubing method. I say it's rich due to the smell of the exhaust.

Now the middle part of the story is that when first started, it was in limp mode - running SUPER rich and I could NOT figure out what was wrong with it. There was a ton of black soot coming out the tail pipe. Turned out that I destroyed the MAF sensor by putting a screwdriver in the MAF sensor airflow tube. Replaced the MAF sensor with a generic parts house unit. Engine seems to run fine except for the poor fuel economy and exhaust fuel smell.

During all this, I had an OBD1 code 12 - MAF (Replaced), and a code 41 - Intake air temp sensor (on order) but that's all. Here's my question: Supposing the Intake A.S. doesn't fix the rich condition, what else can I try?

[centralcoaster33]

I think the TPS, MAF, AIT, O2 sensors and possibly a MAP/BARO are the sensors that affect the AF ratio. Of course you need good injectors, plugs and fuel pressure for that all to work well. I'd check all of those with a voltmeter, then set my idle and timing with a light, then see how it runs. Here's a link to the FSM. That will be helpful for sure!
http://www.nicoclub.com/archives/nissan ... nuals.html
shoot! coming soon... take a look at the 88-93 D21 Series (all) and the 1994 model until then.

Welcome to NICO Club!

[Dogfather]

Thanks very much ccoaster. I replaced both the Intake air and the O2 sensors today. Don't know if that will cure my prob but she sure idles and runs good. I'll do a couple of tanks to see what my mileage is. Thanks for the tips. If the mileage still sucks I'll go down your list. Thanks again!

[centralcoaster33]

Sounds like good progress!