dsmith

I need help on this one.

Symptom: My car has good power up to about 3k rpms. It struggles to get to 4k and really won't go past 5k. It won't go above 80-85mph in 3rd, 4th or 5th. If I push the gas pedal to WOT, the power backs off a bit. If I lift slightly, power picks up a little. These symptoms have been happening for the past 6 months or so, but really didn't show until going on the track (I didn't run around town at upper rpms). The symptoms have been the same through the following repairs, in order. All tune-up items except ignition wires have been replaced.

1. 02 relay blew, yadda yadda, I set the ignition timing wrong (too much advance) and had pinging/detonation above 3500rpm. I think the car pulled well before the blown fuse, but a large oil leak at left side cam cover prevented full throttle driving.
2. fixed fuse and ignition timing, car didn't seem to have full power again.
3. fixed cam cover seals, leak gone, timed cams. no change in drivability.
4. pulled off cat converter and it rattled like bolts in a can. i hollowed it out, some was melted, and put it back on. i reused gaskets and hardware for now. i think it has a small gasket leak, but doubt that matters right now. to my disbelief, no change in upper rpms/WOT! there was a difference up the 3k, though. it passed inspection with CO% at .24 3000 miles ago.
5. adjusted throttle linkage so when pedal is to the floor, the throttle arm just touches the switch enough to work, but it's about 1/8 inch off the stop at the throttle body. any issue with this?

Any comments on the above? I'll probably go for a compression test next, then mixture, but would like some input on what's already done.
Thanks,
David

theiceman

A couple of questions that might sound foolish but what the hell...

What kind of car is it ? an Sc or a Carrera ?

does the car spool up to high rpms while sitting ? can you blip the throttle to these high rpms? or is it only under load the condition exists.

Does the plugs get fouled ? is there black coming out of the back that may indicate unburned fuel due to poor ignition. ?

It sounds like you are getting either fuel fow limitation or failure on you ignition in high RPMs. I would not suggets part swaping but a few things come to mine

Ignition coil . may be craoing out under higher RPMs ( had this one . )
Fuel delivery issues, could it be your fuel pump not giving you the juice? a presure tester would tell you this.
\
Could iyou be losing manifold vacuum due to a crack in the air box that only apears under load , and closes up again ( that would SUCK as you just had the engine out ) .

Anyway just a few ideas.

theiceman

oh I just read the top of the post sorry .. it's an 83 so an SC same as mine . actually to some degree it makes it easier .. ellimintes CPUs and relays.

The other thing could of course be the fuel distributor but that would be remote, if it was fuel it would just be that there is not enough ..

too bad really I have a spare fuel pump and coil you could have tried if you lived closer.

dsmith

yea, i was thinking i better check total advance at 6k rpms before compression. maybe just a distributor problem? it revs freely in neutral at idle. idle is fine too. me thinks the fuel pump is getting louder, but that should really be a good/not good part, so i'm ruling it out for now. i'll report back later.

LaughaC

Could spark be arcing from a wire when under a full load? This happened to my 928 once and had me baffled for days. Re-arranging the wires took care of it.

dsmith

I checked ignition timing at 6k rpms and it's between 20-25 deg BTDC, which is Bentley spec. Does this mean no dizzy issues? I don't notice any kind of misfire, and it revs freely in neutral. I'm off to check spark, wires and visual inspection of cap and rotor.

dsmith

ok, here's a good one. about a year ago, shortly after doing all the tune up stuff (3k miles ago), i replaced the left side block off plate with a used one. mine was missing the bottom ribbed section, so it wasn't directing much air to the cylinders. the used one was older and did not have the relief for the 83 distributor cap. i heated it with a torch and molded the indentation, but it was still touching the wires/cap (yes, i was lazy and uninformed then). looking at the cap and rotor now, both had carbon build up and pitting on the contacts. i cleaned them up, and put on the original block off plate. the car now pulls much better mid and upper ranges. my guess is the cap had undue pressure on it. here's what i'll do now:

-new cap and rotor
-new block off plate
-new exhaust gaskets and hardware
-set mixture

hopefully i'll have good power along with no oil leaks now for next saturday's race.
cheers.

dsmith

Thought I would update some more. I bought CIS fuel gauges and made a switch to work the fuel pump/car off. found the following:

1. engine off, WUR unplugged, valve shut: 80psi system pressure. spec is 65-75, so i removed 2 shims from the fuel distributor and brought it down to 72psi.

2. engine off, WUR unplugged, valve open: 62psi cold control pressure. should be 39-46psi at 90 degrees outside temp.

3. engine off, WUR plugged in, valve open: 62psi warm control pressure (bimetallic strip warmed up), also same with car running and warmed up. should be 50-55psi temp independent.

So, with a combination of bending the metal strip inside the WUR and tapping the plug up and down, I achieved the following:

System pressure: 72psi
Cold control pressure: 40psi
Warm control pressure: 54psi

The good news is that it runs much worse now, and took some mixture trial/error to get running, so at least I know it had an effect! I can't get it to run any better than before, so I'm going to get the mixture set again and maybe dyno checks under load.

I figure once I know the fuel pressures and mixture are correct, I can go hunting elsewhere.
Later,
David

dsmith

Well, I missed the last 2 races cuz I can't yet figure this out. I bought an LM-1 wideband AFR reader, installed it and did the following:
1. Initial AFR was about 18:1! Yikes, I knew it was lean but jeez!
2. I set AFR to 13.5:1 at 950rpm idle and went for a drive
3. On acceleration the AFR climbs very lean. I lifted off at 22:1!
4. After about 20mins of driving, The AFR rose up to 15:1 at idle?? I set it back down and continued, but thought it was strange. The car was fully warmed up when I set it at first.

Also, plug wires measured 3.71-4.17, coil wire 1.13, rotor 5.00. This was end to end, not just the plug connector. Ok or not?

My question is what items would most likely affect AFR in this manner? All fuel pressures and AFR tests are normal at idle. I can rev to redline and the AFR drops to 12.X:1 at idle.

I know it's not enough fuel or too much air under load, and what parts are involved, but which parts would cause such a drastic change? Like, could a bad Freq Valve do it? How could a vacuum leak only be this big at high load, and non-existant the rest of the time?

I'm stepping away for a week, so I would REALLY appreciate some good insight on this one.
David

theiceman

don't forget

- slap self in head .

Mike Murphy

I would change the fuel filter. Then, I might swap out the fuel pump. Sure, you might have good fuel pressure, but what kind of pressure do you have under full throttle? That's a difficult one to measure unless you have a gauge in the car.

theiceman

ah man I must have been missing a few posts , thought you fixed it with your new player and cap .. doh !!!

theiceman

Well definitely looks like fuel , but I would do this to get myself grounded. Put the AFR meter on a known good car and take the same readings, then at least you know what you are working towards. I would do the same with the fuel pressure gage personally. Maybe there is a lister that could help you out.

Mike Murphy

In my experience, a vacuum leak is most noticeable at closed throttle positions, not WOT. The more closed the throttle is, the more vacuum the engine will generate. A good induction system can generate 0 inches of vacuum during WOT.

psychoideas

Hi David,
You quote System pressure at 72psi, but what is your system delivery volume??
Mine's supposed to be 850cc per 30 seconds.

If it's less than that you may not have enough fuel delivery at WOT.