More speed density questions/problems

[88t.birdsc]

Ok, the idle is more stable with cleaning/replacing egr and tab; however, the engine runs rough at idle and has low vac 12". The few times it did run ok engine vac was 16" but it wasn't for long. Now it feels like a low speed miss. It doesn't seem to have a heavy miss at wot. Part throttle feels like it's loading up, has a bad injector, or vac leak because it bucks and jerks. The map sensor setup may be an issue since the check valve bleeds vac. and stops boost correct? The fuel pressure doesn't hold with the engine off. Is this normal for a 255lph and bbk reg? Fuel pressure is 40 at idle and 80 at wot. Timing is 10-12 degrees. TFI problem? What am I missing? I could clean the injectors and do a cylinder balance test. I have to get it better before any other mods. Where should I start? Any ideas?

Thanks,
Mike

[F=MA]

The low vac is a primary concern. No SD setup will work worth a damn on 12" of vacuum. Figure out why that is and I bet you'll solve most of the problems. Could be an internal or external vac leak, maladjusted valves. Block the bleed-off for the check valve and see if it improves. It's gotta be really bad because vac leaks typically result in high idle on sd, not low chugging as on most other systems.

F=MA

[88t.birdsc]

It could be that the timing is retarded 4 degrees, but I seem to remember that it smoothed out once and I was like wow that seems good. How would you check the pedestal non adjustable valve train? Can I check compression which would be lower than normal across all the cylinders? I can also check for vac line and intake leaks.

Thanks,
Mike

[F=MA]

Squaring up the cam absolutely would help since, if you just retarded it by using a multi keyway sprocket, you don't know where it was at originally. Variances as wide as 4 degrees exist between stock cams, installed straight up at the factory. Gotta degree everything.

X2 on checking for vac leaks and doing a compression test. As for a non-adjustable valvetrain, check the spring installed heights and the amount of turn to get it to torque; it should be 1/2 to one turn on a street motor, 1/4 to 1/2 for race. Too little turn and you can hang a valve, which'll burn it in short order.

F=MA

[88t.birdsc]

The heads were e7's off a mustang with an e303. I don't know if installing that cam would require a valve spring modification. I'm not looking forward to tearing into the motor again, but I may have no choice if the other items check ok. The vac. gauge seems fairly steady but low. I'm hoping it is late valve timing and not a burnt valve. Weather sucks right now and the car is outside. Hopefully I will get a chance to work on it soon.

Mike

[F=MA]

I think one of the biggest wastes of time is camming the stock 5.0 HO, unless it's a custom grind built just for the application. the E7 is a flow choke and the valvesprings can barely handle the stock lift and duration. One rev limiter bounce and they are done and the exhaust valves are on their way out. Most I've seen with any miles are putting out seat pressures down in the 50 pound range, on stock stuff. Stress it harder and, well, you get the idea.

P51C

[88t.birdsc]

I would like to get rid of the cheap check valve going to the map. Could I use a regular 1 way vaccuum check valve? Where is the correct way to install the .042" orifice and why is it needed? My check valve has a vaccuum leak all the time through the little orifice on the casing of the valve. It is so noisey I can hear it in the car above everything else.

[F=MA]

I use the cheap little one way valves found in line to Mustang and other Fords cruise control units. Easily available, and I've proven they can take 15 pounds of boost plus. it's mounted so the MAp can see vacuum but not boost. The orifice goes aft of the valve, between it and the MAP sensor. It's needed so boost doesn't hit the MAP sensor's diaphragm and freak out the ECM. Don't put it in and it's like the car smashes into a brick wall at about 3000 rpm.

F=MA

[88t.birdsc]

Ok I must be missing something. If the one way valve keeps boost from hitting the map sensor, why would you install an orifice inbetween the map and the check valve? Is that going to restrict the amount of vaccuum going to the map? My check valve seems all wrong as it bleeds vaccuum constantly I guess untill a boost situation. It just doesn't seem right to create a vaccuum leak albeit I suppose a small one. I'm having trouble grasping what they're trying to accomplish. For some reason I thought they might have wanted me to install this check valve going to the fmu.

Thanks,
Mike

[F=MA]

No valve is perfect; the hole is there to prevent any boost which sneaks past the valve form hitting the MAP, which would have catastrophic driveability effects.

It does continually bleed a little and reduce slightly the vac to the MAP; that's why you have to discover the right amount of leak that protects the MAP but not so much its function is affected and the idle mixture gets super rich. My #42 nitrous jet sized leak has passed emissions testing no problem where I live, using a basic rolling road test.

Don't forget that cars ran on controlled vacuum leaks, in other words, a carburettor, for most of the 20th century.

SD doesn't give a crap about vacuum leaks. It doesn't have any functions, like MAF, to get confused by the unmetered air. You can open the big port going to the brake booster and the car will still start and just idle really fast as the computer tries to work in all this unmetered air.

F=MA