Turbo falling flat on its face

[svomike]

Hey Guys,

I have a 1984 SVO all original, I have an issue with the turbo at the top end falling on its face. I had this question posted on the other SVO site and the first thing they suggested was the fuel, I added octane booster and it is still acting up. The strange thing is, that if I ease into the turbo it usually will climb with no problem, or if I take my foot off the accelerator and accelerate again it will usually straighten up. I know that the 84's have two pumps, if I replace the tank pump with an aftermarket higher flow pump, do I have to still retain the second pump. I am thinking about dropping the gas tank anyway to clean it out completely. I would appreciate any help you guys can give, the car does sit a lot especially with our hot summers, until I can get the AC fixed.

[blueboss]

Hey Guys,

I have a 1984 SVO all original, I have an issue with the turbo at the top end falling on its face. I had this question posted on the other SVO site and the first thing they suggested was the fuel, I added octane booster and it is still acting up. The strange thing is, that if I ease into the turbo it usually will climb with no problem, or if I take my foot off the accelerator and accelerate again it will usually straighten up. I know that the 84's have two pumps, if I replace the tank pump with an aftermarket higher flow pump, do I have to still retain the second pump. I am thinking about dropping the gas tank anyway to clean it out completely. I would appreciate any help you guys can give, the car does sit a lot especially with our hot summers, until I can get the AC fixed.

Do you know what your fuel pressure is doing? And could you elaborate on "falling on it's face", what exactly is it doing? Before you start slinging money and parts at this, find out exactly what's wrong. Pick up a fuel pressure tester. It will help with the diagnosis and save you some cash in the long run. But to answer your question, No, you don't retain the frame rail pump with a high pressure/volume in tank pump.

[Stinger]

How much boost are you running? Are you running premium fuel?

If the turbo is making boost and maintaining it throughout from 3500 to redline, the turbo itself isn't falling flat on its face. Only if boost is dropping significantly as rpm rises is the turbo involved in the issue.

You need to log fuel pressure while driving under boost. Fuel pressure should rise equally with boost (15psi boost increases fuel pressure by 15psi). If the fuel pressure drops while boost is maintained, then you have a fuel flow issue (plugged filter or more likely, failing pump).

You also need to check your plug gap. It should be no more than .030".

How did this problem arise? Did it slowly get worse, just start quickly out of the blue, or done it as long as you've owned it?

[MikeFleming]

From your description this could be caused by one or more of the following (assuming the engine is healthy overall):

- Fuel flow (pressure) not keeping up

Get a pressure gauge on it and check.

- Ignition failing
Spark plugs, cap, rotor, wires, coil, battery cables, charging system, TFI, PIP, wiring, etc.

- Plugged (partial) exhaust
Inspect, test

-Weak valve springs
Replace.

[Kendal Coker]

I have had that happen with bad plug wires. I never would have guessed it would be that but it fixed mine.

[svomike]

I do not think I had this issue before I changed my alternator to the 3G setup, my lights are flickering since I changed it, could that affect it. I am running roughly about 15 to 16 pounds of boost. I have not tested the fuel pressure yet, I am running premium fuel, I have since I had it. The rotor and cap are fairly new, the spark plug wires are tayler 8mm wires, do not believe they are bad. The spark plugs are fairly new, the fuel pumps to my knowledge are the originals. I don't have a lot of miles on anything that I have replaced, because I have only driven it maybe 200 to 400 miles a year starting in 2004. Could anybody tell me what the fuel pressure should be stock at the fuel rail, that will help unless you just think it is electrical/electronic. The sound it makes when it does this is kind of a blahhhhh sound, again if I let of the accelerator and mash the accelerator again it will continue to climb. If I start out and just accelerate normally it will climb fine until it kicks back down, if I stomp on it that's when I get the falling on it's face that I am trying to describe. Oh yeah as far as I know the engine is healthy, 89,000 miles and no issues that I know of.

Thanks for any and all help.

[Patrick]

I've seen bad plug wires do this just as Kendal observed. The car owner swore that he had recently installed plug wires, but new stock wires eliminated the problem.

Fuel pressure:
At idle and ~18" vacuum, 29-31PSI.
At idle and Vacuum port disconnected from regulator, ~39-40PSI
Under boost, add 1 PSI per pound of boost to the above 39-40PSI. (IE, 39 plus 15 would be 54)

[MikeFleming]

Curious that the lights are flickering. What condition are the engine and chassis grounds in? Also check the headlight grounds at the radiator core corners.

[JKLedbetter]

I, too, have had plug wires cause stumbling, but only above ~12 psi.

-Kennon

[svomike]

I will check the plug wires first, then the fuel pressure and then on from there. My lights flickering, I meant all of my lights, inside and out, now that did not exist before my 3G upgrade, I know I am putting out a lot more amps from the new setup and I followed the instructions explicitly. I say all of that and I did use a junk yard set up to save money, but I did use new cable as suggested on the positive and negative side and back to the relay. I will check my ground wires and my new connections, if the 3G alternator I got out of the junkyard is going bad, it would probably affect it I would think. I am really not that dumb on turning wrenches on Mustangs or cars in general, just learning what I can on turbo charged Mustangs, had it for Fourteen years, just have not had to do a lot to it yet. The car was in great shape when I bought it for it's age and of course now it is 28 years old that doesn't seem right but true. Thanks again for the help guys, I would be lost without knowledgeable guys like ya'll, I will keep ya'll informed on what I discover and maybe it will help someone else.

[TheSVOTrust]

I'm with Mike on the grounds -especially the secondary ground and with Kendal on the plug wires and with me on the fuel pump !

Ground can go bad inside the wire or a the connector for the fender well
Plug wires can go bad inside them - like from removing them even though they look nice (many think because they were expensive they can't be bad)
Rail fuel pumps can start and run a car - but be lacking in pressure also . (just found that out) Most said - when they go they just go but there is the pump and just isn't up to snuff !

You know your car - this is an easy one. ONLY look at these thing and you will be fine !!

Mark
P.S. Of course check the JUNKYARD part you put on the car .

[TheSVOTrust]

Most don't do one fix at a time (guess we like to get greasy once and "finish the job" !

BUT this is one car that everyone could learn from ! (Was fine until I changed alternators)

So - once the output of that is checked (and the grounds are fixed) Rebaseline it. (might be fixed or might be better) Not perfect....
I would go to the plugs and wires (if they were changed and gapped too large (wire pulled on more than 2 twice over the years) it will also give the chance to SEE the plug (if fouled from oil - as oil seals rear their heads on these cars with age) FIXED-but not perfect...
Put a guage on it (run it under the hood with the wiper trim off and one wiper holding the guage flat to the windshield) IF it bucks when in boost (and you see the guage fall or NOT RISE like it should underboost) replace the rail pump.

Mark
P.S. Auto store rail pumps won't cut it for our cars (ask me why I know). If you are ok with changing the lines from Bundy to AN I've got a deal for you !!
http://i38.photobucket.com/albums/e136/svo2scj/SVO%20Photos/photo45.jpg