Hey, i just finally bought my first GN, i'm relatively new to the concept of Fuel Injection and turbos with wastegates and what not. I've done alot of modifying to older buicks with carburation and well i got a problem. I bought a 87 gn and when i get at WOT, the boost is about 18-20 psi, and the car backfires out of the intake, always poppin off my boost gauge vacum line, i'm thinkin that it's leanin out bad and causin it, also, on the exhaust housing of the turbo, there is what appears to be a block off plate on the front part of it with 2 bolts holding it on. Is there anything i can do or any books i can use to reserce info on these 3.8 turbos? any help would be appricated. thanks guys.
Matt,
The plate on the front of the turbine housing means it's probably an older "Cheetah" turbo.
The backfire indicates lean/detonation and can have you driving over the shiny parts quickly!
You need to turn the boost down to match the fuel octane (probably around 16 psi), check for fuel pressure under WOT (should be base + 1 psi for each psi of boost), and probably need to make sure you have a GOOD fuel pump and adjustable fuel pressure regulator.
Cruise http://www.gnttype.org, starting with the Spring Cleaning
and work your way to the Performance Recipes
Be sure to use the pull downs on the top of the main page (and this page) to access the RESOURCES and all the other data.
hey, thanks ken, i just got a few more questions to help get me started, how do you adjust the boost on these bad boys?? like where do i start? it's got a bosch fuel pressure regulator on it, but which way do i go to increase the pressure or decrease it? should i turn it in a bit to turn up the psi, or is it opposite of that? i plan on replacin the fuel pump with a better one, and replace all the parts you suggest, maybe go for a garret turbo, does that come wiht the housings on it or just the turbines and stuff. just wanna know. thanks again.
Here's a quick list of some things to check out:
- First, locate the wastegate actuator ... under the turbo there's a "can" with a rod that hooks to a "J" shaped arm... sometimes referred to as the flapper, since it controls a disk inside the housing that covers the wastegate hole. If the rod has threads and a pipe couple (see Adjustable Wastegate then you do the following:
- Remove the C clip that holds the rod on the flapper arm
- Pop the rod off the arm
- LOOSEN the rod by unscrewing the pipecoupler, making the arm LONGER
- Depending on the thread pitch, you will need to turn it down from 3-8 full turns. Coarse pitched threading is usually 1 turn = 1 psi. Fine pitched is usually 2-3 turns = 1 psi.
- As far as the fuel pressure regulator goes ... if it has a allen headed threaded rod and a jam nut on top, then it's adjustable. To raise fuel pressure screw the threaded rod IN and the converse to lower pressure ... obviously, a fuel pressure gauge is a good idea doing this. Pull the vacuum hose off and adjust the base pressure and then reattach the hose. A good starting place would be 43 psi or so. The fuel pressure gauge will screw on to the end of the fuel rail (you remove the metal cap that's probably there now)
- As far as turbos go, that one may be just fine with some tuning. I wouldn't jump to changing it until you have a chance to do some basic tuning and sorting out. It could be just fine. As far as buying turbos, they normally come as a complete unit
hey, well finally took the car to the track, first run, did pretty good, a 14.7, not bad, should be better i think, turned the turbo up to 15psi and turned the fuel psi up, started leanin out, so i gave up on that one. I would like to have my car run in the 13's, then i'd be happy. Are there any books or manuals i can get that are good on info on these cars? thanks again.
I've moved this thread since it really wasn't appropriate for "Engine Mechanicals".
I can't imagine any information you'd need that isn't on this site somewhere. Take a look at the 'Spring Cleaning' and 'Performance Recipe' links mentioned above. If you've read those two areas and heeded there advice, 13 second passes are trivial.
I have recently bought my first 87 GN. I know very little about the quirks. I have run into, what possibly could be a very minor problem. When I turn the car over after it has sat for the night it will idle for a minute or two and then cut out. Once the care warms up I never have any trouble. Is this a common problem with GN's?
Sounds like the injectors may be leaking down (or the fuel pressure regulator).
Take a look at:
http://www.gnttype.org/techarea/fuelsystem/fpsys_check.html
and
http://www.gnttype.org/techarea/fuelsystem/fuelpage.html
for some troubleshooting steps...
i live in england and have an 87 gn,ive built the engine and transmission myself adding certain performance parts on the way,i dont know if i have the correct combo yet as i running it in.i have a poston cam 36lb injectors with poston chip,poston headers, down pipe&crossover,2800rpm t-convertor.what fuel pressure should i run on idle?with vacumn off.what sort of times should i expect as is?
Andy,
I saw no mention of an upgraded fuel pump or a scan tool. These two are a must. General rule of thumb on fuel pressure is around 43 # static with the vac hose off. This is only a ballpark figure as you need to monitor o2 #s at WOT as well as checkig the int and blms at idle. I dont recommend that you run wot or turn up the boost until you have a scan tool to tune the car with.
If you go to the basic recipies on the GNTType web page it will give you a lot of info to work with. Also go to Ken Mosher's webpage http://www.turbo-link.com/ for a great comparison of scan tools.
Dwight