Issue under load or WOT

aviationstation

Registered User
I have a 95 SC 5 speed with 77k miles that, when I first purchased it, would miss & ping under load. I've recently replaced the Cam Position Sensor, plugs & wires & now it runs considerably better. However, under load or near WOT I get some pinging (even when cold) & the powerband seems a little choppy near the 3000~3500 and up range. I get a max of about 10~11 lbs boost & once and a while I hear a faint hiss (under load).

So, I'm hoping someone here can yea or nay what I speculate might be the problem...

To me it seems that there might be an intake and/or under boost (pressure) leak that:

Would limit boost to 10 lbs
Leans the mixture (intake leak) & causes the pinging
Results in the intermittent hiss sound under load ot WOT

The car runs great otherwise & I just resealed the upper IC tube & propane checked it.

Thanks!

M Randolph
 
u have a pretty big vacuum leak, what is ur vacuum at idle? how many inches? maybe it has a tank of low grade gasoline, if u suspect that it has a tank of low grade gasoline then i suggest u lay off the boost until its used all up. Also, check the plugs, maybe never got OEMs or identical ones, i suggest u get some AUTOLITES double platinums. Try to see if u get any codes out of it.

when it leans the mixture that is because u do have a leak, it is pulling un-metered air.
 
Darkstar,

Thanks for the info. Yep, the gas is fresh 91 OCT with some Moroso octane boost right outta the drum. Should be about 93/94 where its at. It behaves the same way on pump or mixed (with additive) fuel. The vac at idle is around -18~-20 (I think).

The plugs are AutoLite platinum & the wires 8.5 mm, so the ignition is sane. Do these cars typically see boost above 10~11 under WOT? If my reading is low I need to determine if its instrument error or an actual leak. I suspect a leak, though, based on the lite pinging and the air sounds (intermittent hiss under load) I'm hearing.

Thanks again!

M Randolph
 
The vacuum/boost refrence hose going to your fuel pressure regulator may be leaking. Under boost it is supposed to increase the fuel pressure pound for pound with boost.

If the fuel pressure isn't increasing, the car will run very lean and feel sluggish and ping under WOT. The hissing sound could be coming from the hose.

David
 
I've had that problem, some pinging and a hiss especially when I turned the car off. The cause turned out to be a hole in the bottom of a hose after the PCV, 1 goes up to the plenum but the other went out to the pass side.
I had the pinging without the hiss on my 5Sp which has EGR and the silicone hose was unplugged I got a code 33. I think the 94 & 95 5speeds may have 2 silicone hoses.
Good luck
 
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