951Saga

I’m in the process of replacing all the exhaust gaskets mainly due to leaks at the head ports #2 and #4.

Once the crossover was off I found a distinct difference in color between the two ports, so I pulled the spark plugs too.

What are the potential causes? Is it safe to take a three hour trip if I’m easy on her?

TIA!

To be clearer… spark plug order is 4-1 from left to right.

The light color collectors are for cylinders 2 and 3.

Fluidplay

Really find this interesting as I discovered the same situation recently. I had just installed a Link ECU, new harness and all associated mods to make it work and found #2 & #3 cylinders running abit hotter. I thought maybe the injector pulse was off on these cylinders, but all checked out good. Would be interesting if this could be validated if this is common with our cars running stock and/or otherwise systems.
I noticed this when I placed a thermal gun to the exhaust manifold. The readings were surprising #1&2 were running at about 80c, where 2&3 were running at 200c...big difference. There were some logical reasons posted, but still can't figure out why.

My post "#2-3 exhaust manifold running hotter"

lart951

what's your setup? do you have wideband, what's your a/f ratio?

Tedro951

AF ratio would be an average of all 4, so it may not be conclusive. The IR thermometer is your friend. It would be interesting to check the temps under a little boost..like on a dyno. Air distribution at idle would be my guess, and I'd also believe that the temps would get much closer together under boost. Just thinking out loud...

951Saga

Hey Fluid, I did a search but didn’t see your thread, obviously failed to use the right wording. Did you pull your plugs and find them to read similar?
I’ve been meaning to pickup a thermal gun, but have not really determined which would be best.

Well Lart this is a Frankenstein stock setup. ’89 parts bolted to a remaned ’86 block with an ’86 AFM, my original AFM door drags in the housing. Other than that the plug wires and diverter valve are not stock.
I have a wideband in the box and test pipe with out a bung hole, so no AFR numbers unfortunately.


If this has any bearing, I pushed her quite hard at the Fest’s Friday track day a few weeks back.

-When started cold, the idle is good, but poor surging power until it warms up a bit. I don’t dip into boost until the oil pressure indicates it’s at temp.

-Once warm, the idle is somewhat erratic, but no big fluctuations. Power on boost also surges a bit. I figured this was due to the exhaust leaks, but could be other issues… waste gate maybe.


Once I pull the manifolds off we’ll see how they look.

I need to be on the road tomorrow so I may just button it up and keep it off boost for now.

Tedro, any suggestions on a good thermal gun or at least a temp range to look for?

lart951

I dont think there is any difference between afms, how about boost? stock?

951Saga

Man you’re up early Lart!

Yep boost is stock too.

Tedro951

I'd get the harbor freight gun. The range wont matter at idle, but a more expensive gun will go to higher readings. The wastegate shouldn't cause 2 cyls to go lean, but might cause the surging under boost. Intake gaskets are the simplest explanation for the lean cyls, but its prolly deeper than that.

lart951

My eye gun tell me you are definitively running lean and hotter on those two. Find the reason for you must.

951Saga

OK Ted, -58 to 1112*F looks good for $60. If they have it in stock I’ll have one tomorrow.

Agreed Lart! To the garage I go… will get the exhaust strait then test injectors, check/ replace intake gaskets. Wish me well.