Hi all!
I have recently changed the head gasket on my 1993 Ford Telstar TX5 Ghia (Same engine as Mazda 626- 2.0L I4 DOHC). I have encountered a couple of problems/symptoms upon the first start:
- Extremely black spark plugs
- Missfires along with dips in RPM (missfires happen every 0.8 seconds I'm guessing)
- Every missfire, there is a 'putt' noise from the exhaust
- Dark smoke when revving
- Hesitation when revving
- Takes a really long time to start
- Struggles to idle by itself for about a minute or so, so i have to keep my foot on the pedal, then I can take it off.

There are 2 sensors, both measure the coolant temperature and they are located next to eachother (one is black, one is green). Get this, they both broke before I put the engine back together So I DID believe that they were the cause of the given symptoms (rich running), because the broken sensors were telling the ECU the engine is cold. So, I went about bypassing the sensors by directly connecting the 2 wires leading to the sensor. The fans came on but the engine still had the exact same symptoms. This would also conclude that they are NTC thermistors, because when hot, there is decreased resistance (in this case, with broken sensors, there is infinite resistance and the ECU thinks the engine is EXTREMELY cold).

Well the sensor bypass proved to be ineffective, so now I think I may have timed it wrong. I kinda guess timed it, which makes it more likely that I got it wrong. I inserted a long pole in place of a spark plug on no.1 cylinder to find TDC. Then I got the timing marks lined up and put the belt on.

So my question is, would the listed symptoms be caused by bad timing?
Thanks!

 

Remove the timing cover, rocker cover & crank pulley. There is timing marks on the crank & cam shaft/s. Check that 1st. next replace both the damaged sensors, then fit some new spark plugs and go from there.