Newbie needs help.

[Terrier]

Sorry for another boost post but I am not real familiar with turbo cars. Anyway I bought a 85 SVO that starts perfectly and seems to idle just as good. When you accelerate it builds boost to a point then almost shuts down. It does not break up just kinds falls flat on its face then when you get out of the throttle its fine. The previous owner for what its worth said it pulled great up until he pulled motor out to change the rear main seal. I have checked the timing and it looks to be at 10 degrees. I have noticed one or two caps in place where it looks like there was vacuum lines but am not sure they would affect it. Where would you guys start in diagnosing? Any help appreciated.

[svono50]

Everyone has to start somewhere and each car is unique, so feel free to fire away!

Based on your description, it almost sounds like your knock sensor is going off, which triggers the EEC (computer) to pull the ignition timing to stave off further knock and potential engine damage. The car will either level off on acceleration or can even feel like it is falling on its face. To get the EEC to 'reset' you get off the throttle and roll back into it. If the knock sensor senses more knock the whole process starts again.

Now, since the PO noted that the engine was pulled to replace the rear main seal, there are other areas to make sure were connected back up correctly. One area that can be mixed up is the boost control for the turbo, which consist of (2) hoses and they typically get swapped around, which creates a no boost situation...but you noted that yours builds boost.

How much boost do you notice before the engine lays over? Factory settings are 15 psi in 'premium' setting and 10 psi in 'regular' setting on the console fuel switch for reference.

A place to always start with our SVO's is the condition of the ignition system. When you go into boost, it requires more energy to fire off the spark plugs, so any weak link in the system can let the flame blow out and trigger the knock sensor or simply lose power. Factory Ford/Motorcraft parts generally work best on our cars, from wires to cap/rotor to 'simple' copper plugs of the proper heat range. Sounds like you verified the ignition timing already, so good to go there. Let us know any additional questions and post up some pics of 'stuff' you are not sure of and someone here should be able to let you know if it is indeed 'wrong' or 'right'.

[Terrier]

Great info thanks for the help! So it seems to build about 7lbs or so of boost then shuts down. The plug wires are ford and look to be in good shape. I have not pulled any spark plugs yet to see their condition or what they may be gapped at. I tried disconnecting the knock sensor and driving it but it did the same thing so I reconnected it. Are there any vacuum lines that could affect this?

[svono50]

Ok, that boost number helps focus the picture a bit. Plug wires can look good, but still be leaking current. One way to see if they are is to check them when it is pitch black out, where you can see the potential leakage current that can vary from a soft glow to actual arching. Obviously you can't fully load the engine/ignition as in driving, but revving the engine will put a little load on the system and may point out some 'leaks'. Measuring resistance of the wire won't always expose a 'bad' wire either.

For plug gap, I always recommend gapping to the minimum, since that gap will only increase with wear, so best to give the plug the best chance to make the spark. Also, stay away from the platinum and iridium plugs, they require much higher spark voltage and don't mix well with our systems.

The vaccum lines that could effect boost levels are typically the boost control hoses on the passenger side fender area. So our wastegate actuator is a 10 lb unit, so if you plumb straight from the turbo outlet to the wastegate actuator you should run ~10 lbs all day long. When you put the fuel switch into 'premium' mode, the boost control unit actually 'limits' the boost signal to the wastegate to allow up to 15 lbs of boost. If you have a leaking boost control hose, you will typically see high boost levels, since it will bleed off some of the actuator signal pressure. Low boost levels could be due to a 'weak' actuator spring, where the exhaust pressure overcomes the actuator spring and allows the wastegate valve to blow open. Another potential cause for low boost is an exhaust restriction (i.e.- clogged cat), where you can't generate enough exhaust flow to spool up the turbo. Yet another cause of low boost is a worn compressor wheel or a oil coked up center housing creating friction on the compressor/turbine shaft.

Does your turbo have a water cooled center section or is it still just oil cooled? The 84's came with a non-water cooled turbo, that was regularly replaced under warranty due to oil coking issues with, from what little I know, a water cooled turbo and water line kit to match the 85-86 model setup. Being the owner of an 86, I am not 100% certain on the details of the earlier models and what Ford did to combat the issues surrounding the non-water cooled turbos.

[Terrier]

I will try looking at the plug wires at night first. I believe the turbo is water cooled because it looks to have a coolant line running to it. We can eliminate the cat being clogged because it is not running one. Previous owner put a custom exhaust on it. I will look into these things you mention and get back to you. Really appreciate the help!!

[GAboySVO]

Double check that your VAM hose is not collapsing. Its should have a wire coil inside to prevent it from collapsing. If you can squeeze it flat with your hand, then you have found the problem.

[Terrier]

Will do thanks. Does anyone have a pic of the VAM hose?

[GAboySVO]

It's the black bellows hose connected to the turbo.

[Terrier]

Easy enough thanks!

[Terrier]

Fixed!! It was the VAM hose. Took it off and the spring inside looked like a birds nest. Corrected it and now runs like a champ. Thank you all for your help!

[svono50]

Glad it was an 'easy' fix...enjoy the boost!