Hey All! I just recently aquired my first 7 (Finally), its a 87 Turbo2 model, all stock. Anyhow after driving it a bit I have noticed that the car sometimes will give me irratic throttle response when I press on the throttle. Now this seems to only happen at night when the engine is cool, it wont do it when its been warmed up for a while or has been sitting under the hellacious california sun. But to explain what it feels like, when you push on the throttle the car getts jerky, not like loosing power but like getting spurts of power, like a boos spike or something, it's quite embarrasing really, car shakes around back and forth making me look like I can't drive a clutch. this will go on for about 10 minutes or so, once the engine is warm it stops doing it.

I am thinking it might be a turbo issue, when I purchased the car, the original owner had the engine rebuilt 3 months prior, the place that rebuilt the engine also offered her to have the turbo rebuilt for an extra 500$, She refused so according to her "the turbo doesn't work". Now I spent some time under the car to check the turbo, and to me it seems fine, spins somewhat freely no scraping or play out of it. It seems like it should operate fine (or at least according to the description in the shop manual). So I am thinking the shop that rebuilt the engine was trying to take advantage of the previous owner because she was "a woman", and because of her refusal, they had to cover their asses from their con and disengage the turbo in some fashion (I'm thinking the waste gate). So while I was under the car and I tried testing the actuator that is connected to the flapper within the manifold, but I can't move it, supposedly (once again according to shop manual) you should be able to compress the actuator with your own hands, I could seem to do so while it was installed in the car. My hypothesis is that some how the wastegate was jammed in a form to allow most of the boost to be bypassed. the only test I could do so far is the "Home Depot Atmospheric BOV conversion kit, a la swing check valve" and see if I get a "pshhhhh." Well I do, but its quiet, according to a DIY article on teamfc3s.org, it should be loud as hell. Also I am not sure wether I should notice the boost when accelerating being that s4 turbos are rated around 5 psi. When I am accelerating throughout the rpm band up to about redline, it feels pretty constant, no rush of power so to speak.



So from this long winded story I think I have two questions. One, do you think the irratic acceleration could be caused by the funky turbo configuration or maybe its something else? Two, any ideas what might be causing my lack of boost?



one more thing, the shop manual says to use a pressure guage to test how much boost is being pushed into the intercooler, I've looked and all I can seem to find is tire pressure guages at all the auto stores, anyone know what I am looking for and where to get one, also how much $ it cost.



Any feedback is much appreciated



Greg

 

Get a boost guage?

 

i noticed with mine the amount of power you have is related to outside temps, as the intercooler heat soaks you go slower



mike

 

Yeah, the difference I've noticed with that is a lot more than you'd expect.

 

Also, on the boost guage in the dash, when I turn the ignition to the point that the electrical systems activate, the boost guage will rise to zero but once the engine is started the needle drops dead. I addressed this problem over on teamfc3s.org, someone said to check the boost sensor, but I guess he was too busy to answer my question on the whereabout this sensor would be hiding. Anyone know where I might be able to find this elusive boost sensor??



another question, should you spin the turbo turbine by hand, how freely should it spin?? I know oil is supplied to the turbo, I was just curious if it should only do a few rotations or should it spin like a top and take a few second to stop spinning?

 

when the engine is idling the boost is negative



mike

 

That I didn't know, but is good to know mike! Although, the needle stays in negative even at WOT nearing redline, I am sure I should be getting some activity out of it. Man I wish I had the time and money just to pull everything out and inspect it one by one.

 

BTW, the bucking you are experiencing when you get on/off throttle is your TPS in my opinion.



thermal expansion doesnt play well with the plunger style TPS, it will be out of adjustment until the car gets to the temperature it was at when last adjusted. (which was likely at operating temperature which is the correct procedure)



Switching to a rotary style TPS should eliminate this problem, so if you go with a standalone ECU you would likely eliminate this. You could try readjusting your TPS and possibly improve the situation, but since you claim it goes away once it's warm this is probably not the case... It might be possible to switch to a rotary TPS with the stock ECU, they are, after all, just variable resistors... just have to make sure the resistance is the same for the same positions...





just my $.02

 

Cool Beans Pengaro! That would make sense why it doesn' do that when the car has been either sitting in the sun or after being warmed up a bit. I'll have to investigate adjusting the TPS a bit more, cause I really don't want to futz anything up. But thanks!

 

Well and interesting addition to my situation, today as I was going to work 6:30pm CA Time, to my amazement the boost gauage was actually working, when opened her up, the needle would rise, and when I let go it dropped, only thing was it was only making it far as 0 maybe a hair more. So if the boost guage is still accurate, I know I aint gettin shiznit for boost. So I know something is wrong. But now here's what driving me nucking futs, when I was coming home tonight 11:00pm the boost guage wasn't registering anymore. deadline all the way to 6K rpm. Now I am not sure why this is, and I am stupified for why it's doing it, unless the boost sensor has the same issue as what Pengaro was talking about the TPS.

Any Ideas??