Running lean and hot
07-24-2013, 11:17 PM
#1
Burning Brakes
Thread Starter
Running lean and hot
I'd like to pick some brains here as to whether I cured my problem(s).
'82 US model. Owned about 2 year, put about 10K miles on it. Currently at 49K miles.
Heading to Sharks in Nowhere (about 200 miles) I notice engine ping during hard acceleration. Never happened before and thought maybe I got some bad gas from BP.
Leave the event late that evening and I notice the temperature gauge is near the 3/4 mark within just a few miles. Once on the highway, it drops slightly but still well over the ½ mark. Accelerate hard and I get detonation.
Normally my gauge reads just a hair above the ¼ mark.
Arrive home and park it. Next day I decide to wash it before working on it. I have upswept exhaust tips and when I got to the back I notice a quarter size bubbled area of the bumper. I wanted to puke!
At least it's out of normal sight and I have some spray and clear ordered. May still let Hagerty cover it. 
I take the car down the street and back for a test run and the gauge is up to 3/4 and the exhaust system is HOT.
Pull the plugs and all are uniform but much whiter than I'd like. Pull a vacuum on both fuel pressure regulators and fuel damper. All hold, no fuel leaking through.
Fuel pressure is 35 psi bridged. Drops instantly to 0 when off. Make a remote switch up the engine compartment. Turn pump off while crimping supply and pressure stays. Bad check valve which explains the hot start issue that's been haunting me. Remove check valve, free up internals with a small wire, clean and reinstall. I now hold at 30 psi for about 30 minutes, it eventually drops and holds at 20 psi for hours.
One problem solved (still ordered new check valve too) but I doubt that has anything to do with the lean condition.
Fuel pressure running at idle is around 27 psi. Remove vacuum source from regulators and it jumps to 35 psi. I think 2.5 BAR is closer to 30 psi so I'm still not sure if one of my regulators are faulty?
After 30+ years, some of the vacuum lines aren't exactly snug so I clip the ends to make a tighter fit on the nipples. I then get to the Thermo Valve near the #4 cylinder and the one line falls off when I touch it. Ends of those two were cracked and brittle. Clipped off the bad sections and reattached.
Put everything back and started her up. Let it idle and the temperature hit slightly above the ¼ mark and stayed there. I hit the back roads ran it through its paces hard with the A/C on and it stayed at the ¼ area. Detonation/ping also gone.
When I got home I put my hand on the body area above the exhaust tips and it was just warm to the touch as usual.
Sooo...now I'm not sure if this is one of those things that decided to cure itself and will pop up again a few hundred miles from home or would the bad vacuum connection at the Thermo Valve have caused this? Guess I could pull that hose and try it again but I'd rather not.
Should I be concerned over the 27 psi fuel pressure at idle?
As an added bonus, I waited 45 minutes and she started instantly. No more embarrassing 10 seconds crank times when hot.
'82 US model. Owned about 2 year, put about 10K miles on it. Currently at 49K miles.
Heading to Sharks in Nowhere (about 200 miles) I notice engine ping during hard acceleration. Never happened before and thought maybe I got some bad gas from BP.
Leave the event late that evening and I notice the temperature gauge is near the 3/4 mark within just a few miles. Once on the highway, it drops slightly but still well over the ½ mark. Accelerate hard and I get detonation.
Normally my gauge reads just a hair above the ¼ mark.
Arrive home and park it. Next day I decide to wash it before working on it. I have upswept exhaust tips and when I got to the back I notice a quarter size bubbled area of the bumper. I wanted to puke!
At least it's out of normal sight and I have some spray and clear ordered. May still let Hagerty cover it. I take the car down the street and back for a test run and the gauge is up to 3/4 and the exhaust system is HOT.
Pull the plugs and all are uniform but much whiter than I'd like. Pull a vacuum on both fuel pressure regulators and fuel damper. All hold, no fuel leaking through.
Fuel pressure is 35 psi bridged. Drops instantly to 0 when off. Make a remote switch up the engine compartment. Turn pump off while crimping supply and pressure stays. Bad check valve which explains the hot start issue that's been haunting me. Remove check valve, free up internals with a small wire, clean and reinstall. I now hold at 30 psi for about 30 minutes, it eventually drops and holds at 20 psi for hours.
One problem solved (still ordered new check valve too) but I doubt that has anything to do with the lean condition.
Fuel pressure running at idle is around 27 psi. Remove vacuum source from regulators and it jumps to 35 psi. I think 2.5 BAR is closer to 30 psi so I'm still not sure if one of my regulators are faulty?
After 30+ years, some of the vacuum lines aren't exactly snug so I clip the ends to make a tighter fit on the nipples. I then get to the Thermo Valve near the #4 cylinder and the one line falls off when I touch it. Ends of those two were cracked and brittle. Clipped off the bad sections and reattached.
Put everything back and started her up. Let it idle and the temperature hit slightly above the ¼ mark and stayed there. I hit the back roads ran it through its paces hard with the A/C on and it stayed at the ¼ area. Detonation/ping also gone.
When I got home I put my hand on the body area above the exhaust tips and it was just warm to the touch as usual.
Sooo...now I'm not sure if this is one of those things that decided to cure itself and will pop up again a few hundred miles from home or would the bad vacuum connection at the Thermo Valve have caused this? Guess I could pull that hose and try it again but I'd rather not.
Should I be concerned over the 27 psi fuel pressure at idle?
As an added bonus, I waited 45 minutes and she started instantly. No more embarrassing 10 seconds crank times when hot.
07-25-2013, 08:34 AM
#2
Rennlist Member
Sounds like you did a great job fixing it.
Not sure about the idle pressure.
Our 85 ran lean, white and hot. It was also fuel related, had some clogged injectors.
Not sure about the idle pressure.
Our 85 ran lean, white and hot. It was also fuel related, had some clogged injectors.
07-25-2013, 10:22 AM
#3
Nicely done.
Had an S4 that was getting 27 MPG (really lean) on a long trip with a very hard start issue. The FPR was bad and once that was changed, everything was good.
Had an S4 that was getting 27 MPG (really lean) on a long trip with a very hard start issue. The FPR was bad and once that was changed, everything was good.
