E30 power loss

[6670charger]

Well, I've changed my head gasket for the second time in six months after finding that one of the new head bolts I put in the last time apparently loosened a little. When I was removing the head, all of the head bolts made a distinctive snap as the torque came off except for one, which gave slight resistance before it turned. The gasket actually appeared to have been in good condition. 

Since putting everything together, the car seems to be running and idling fine except that all of the newfound power that the engine had after the last gasket change seems to have vanished. It's almost like I'm driving my 90hp 4cyl VW I had in Germany a few years back. I'm certain I have the timing set right and there are no leaks I can see or hear. After 1000 miles the engine oil is still normal in color and no loss. The coolant is also fine. I did change spark plugs as a couple of the ones that were in the engine did not seem to want to tighten properly, so I changed to Autolite plugs instead of the Bosch's that I had. Not sure what else to check.

Does anyone have any other ideas or areas to look?

 

Thanks.

[KaiserRolls]

Was the head decked/pressure tested?

[B C]

First thing's first, do a compression test.

Second item that would produce a universal power loss would be a clogged cat or a horribly restricted air filter. 

I say start there. 

[straight6pwr]

its a pretty good rule of thumb that if you didn't have a problem, then you did some work, then you suddenly had a new problem, its something you changed.

 

[6670charger]

I think I determined my problem; spark plugs.

Upon further investigation, I found that 5 of 6 of the spark plugs had not fully tightened when I installed them. I stopped by a parts store to pick up a different set in the event that the threads on these were not quite right, and found while looking at the picture of a different set that the small silver ring that threads onto the plug was on with the flat side facing the head, which was reverse of the way I had put mine on. I pulled all the plugs, reversed the direction of the silver rings and put them all back in; all tightened the way they should. In all of my years of changing spark plugs, I never knew that the direction these things were put on the plug made any difference. In fact, I'm not altogether certain that the plugs I use in my 66 Dodge even have these rings on them.

I think what was happening is that I was losing compression at the spark plugs due to their not tightening enough to keep all pressure in the combustion chamber where it belonged. The car accelerates much better now. I may still be losing a bit of power due to the fact that my muffler is about shot, but at least the car runs more normally.

[B C]

Flat spot on the washer???

Autolites are nobodys friend

[jc43089]

Ngk plugs are where it's at.

Sent from my 831C using Tapatalk

[6670charger]

19 hours ago, Snap said:

 

 

 

Flat spot on the washer???

 

Autolites are nobodys friend

Autolites weren't my first choice, but I had to have something and that was what they had in stock. I'm looking for different plugs. Ideally I'd like either Bosch or NGK. 

[6670charger]

17 hours ago, jc43089 said:

Ngk plugs are where it's at.

Sent from my 831C using Tapatalk

I had good luck with my Bosch plugs but would like to try NGK. Is there a particular version of them you recommend?

[B C]

1 minute ago, 6670charger said:

I had good luck with my Bosch plugs but would like to try NGK. Is there a particular version of them you recommend?

 

NGK ZGR5A, gapped to .032" is my suggestion for a stock M20

[jc43089]

I use the v power usually. The price is good, my e36 had the fancy 4 ground ultra plugs in it, I replaced them with ngk plugs which are OE and it gained 2 nog and ran noticeably better. I am not a fan of the iridium and other fancy metal plugs, none conduct as well as copper. The special metal ones are designed to last a long time, not provide better performance.

Sent from my 831C using Tapatalk

[B C]

This is true^^

 

My van has a label in the engine bay explicitly calling out the use of ONLY a particular multi-prong iridium plug. After replacing them (with basic silver/copper single prong plugs) I can appreciate their consideration for not having to access the rear 3 cylinders any more frequently than necessary.  

 

Although, in a performance application, you could argue that the smaller diameter of the iridium electrode provides additional exposure to the mixture for flamefront propagation. 

[6670charger]

18 hours ago, Snap said:

 

NGK ZGR5A, gapped to .032" is my suggestion for a stock M20

I'll take a look for them. I'm sure I'll have to order them from somewhere as nobody around where I live seems to stock plugs for an M2O beyond either autolite or Motorcraft. 

[B C]

ZGR5A is typical over the counter stuffs, no prescription needed.