The problem started when i had a friend work on my car. All he did was install a s clutch line and when i got the car back it wasnt running right. If i floored it it would hit fuel cut and fall flat on its face. It was showing loads of over 300 when i used to see loads around 255 to 260. It wasnt a boost leak because i tested it and all the was leaking was the tb seals and i replaced them. I thought it was something with the maf and bought a new one and that fixed my problem. All during the troubleshooting i probably hit the boost cut about 5 or 6 times and every time i let off the pedal right away.

Soon after this i kept get the cel knock light coming on when i never got it before. I started doing some logs and the knock count got as high as 8 counts but for the most part it would only hit around 4 counts. It wouldnt knock every time i got on the car it would happen inconsistently and sometimes even at part throttle.

I tore apart the whole area where the clutch line was installed to see if anything was disconnected or cut or broken and i cant find anything. I cant find anything rattling or anything that would cause a phantom knock condition.

I figured maybe it was the tune since it was getting colder around here and i kind of brushed it off. Last week i went to iveys to get cams and head studs installed and when he was tuning the car he said i had bad gas and he couldnt get the timing too high because of it so my numbers we low (350hp 350tq). So ive ran a few tanks through and its still getting the intermittent knock.

I decided to troubleshoot it again the other night. I pulled all my spark plugs and realized they were gapped to .032 instead of .022-.023. When i first installed the plugs i didnt gap them assuming the were factory spec and didnt have a problem for about 5000 miles at least. I regapped them all to .022.

While i had the spark plugs out i did a compression test. Here is where the stress starts! The first 3 cylinders (1 being the passenger side cylinder) were at about 160psi. I get to the last cylinder (the drivers side one) and i reads a lot lower at about 125 or 130. The strange thing is I dont have a huge noticeable oil consumption and the spark plugs werent fouled at all. I didnt try the oil in the cylinder test yet to see if its the ring but i plan on trying that tonight when i get home. I didnt recently fill up my coolant overflow because it was almost empty but I thought that maybe i didnt fill it up enough from when i did the throttle body.

my question is what does it sound like it could be and how could i test it before i take it back to the shop?
Here is what i plan on doing.
Redo a compression test and try the oil in the cylinder and see if it seals up the ring. If it does i know its a bad ring.
If it doesnt fix it what could it be? Bent valve? Leaking head gasket? Maybe the head lifted a little before i had head studs in?
I dont have everything to do a leak down test so i would have to bring it to the shop for that.
When i drained my oil last i didnt notice any coolant in it nor do i see oil in the coolant although the coolant in my overflow looks a lot darker then coolant usually is and before i topped it off it looked almost yellowish.

If I have to go through the motions of pulling the head Im at 50000 miles now should i go ahead and get the timing belt and water pump replaced while everything is taken apart?

Thanks for every ones help!

 

Ill add ciff notes for the lazy if this will help wit responses.

Car intermittently knocks
did compression test and it was 160 160 160 130
consumes a little bit of oil but not a lot and i also think it has been consuming some coolant.
Have to still redo the compression test and try adding alittle oil to see if its the rings.
what else could it be?

 

here are some pics of the plugs. When i redid the compression today it read 160 on all 4. When i look down the spark plug hole it looks like there is buildup or some oily residue on the top of the pistons. The other 2 look clean.











let me know what you think

 

Did you change to a different gasoline from a different service station after Sean Ivey pointed out the low octane problem? Are you still on the stock pump and injectors? There is no Walbro upgrade listed in your mods.

 

Yea i have a walbro with stock injectors. I did switch to a different gas station as well.

 

At what RPM do the knock counts start to appear? Is it upon throttle tip-in?

 

sometimes its on tip in..sometimes i can be WOT on it and it wont knock at first then start around 5000 to 5500 and then sometimes it wont do it at all. Ive read of people lifting the head and having a small head gasket leak that sprays coolant into the cylinder and causes knock. I have to watch my coolant level close to see that though. I thought it oculd be phantom knock from teh downpipe because its pretty close to the body of the car but i head wrapped it so it wouldnt bang against anything loud and that didnt help. The only thing that actually made it occur less often i think was the spark gap.

 

Maybe you should drop it off and have is diagnose it?

Sean

 

+1
Bring it in before it get really expensive.

 

I plan on it sean. I was going to call you this week. Are you guys around on the weekends too?

 

i brought it to ivey and he is looking at it today. I never had someone from a shop actually sit down and talk to me for about 15 minutes to figure out the problem. I know my car is in good hands and Ill update everyone on what he finds.

 

^^^ whats up? Your dad was pimpin the classic porsche. nice....

 

It made 370 on the dyno, but still knocks intermittently. Had a nice boost leak which we fixed. What gets me is how random the knock is.
Still working on it.............

Sean

 

Internal knock? Ask him to try meth or a gallon of c16 to see if that helps....

Lifter tick? Exhaust rubbing?

Dan

 

thanks sean! im glad the car is making more power now but the knock is killing me! I hope its some stupid little thing that i over looked and not something internal.
Im not sure if it will make a difference but i have another MAF sensor in my trunk if you want to try swapping it out. That was something i initially tried when i was having the fuel cut problem and since then i put my original one back in.

90GSXDan - My lifters actually quieted down after the cam install. They used to be a little noisy since i bought the car. The knock started happening while they were still noisy and continued after the cams were installed and once they got more quiet.