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hplar
06-20-2005, 08:44 PM
Ok this is going to be a long one but I need help. I bought an 87 GN from my uncle who added parts with no rhyme or reason. The problem I have been chasing for a year is when you punch the car the boost goes to 20lbs and almost immediately drops to 10. It slowly builds back up and then drops..... then builds and stays. It feels like its going to pull like a frieght train and then fags out. It pulls like hell up top but the fluctuation in the middle is terrible. Here is what the car has on it.

Stage 3a turbo from atr
33 lb injectors
cold air intake..atr
7th injector
pitbull chip..atr
3" down pipe..atr (does the turbo need to be ported to match)????
2400 stall converter
2 1/2 stainless exaust with free flow cat
upgraded plenum plate
Double pumper gas pump..atr
Like I said I have been haunted with this for a long time. I replaced gaskets, changed vaccum lines, ect. ANY help would be greatly apprreciated!!!

R

Keller
06-20-2005, 10:01 PM
Sounds like he just got out his wallet and went crazy in the ATR catalog...in the mid '90s.

- Not sure what the "Stage 3a turbo' really is, but someone else may know. Depending on age, it may be a TA48/TA49 equivalent.

- The 7th is likely not necessary if you had decent capacity injectors. i.e. ~36 lbs. Old technology.

- Pitbull chip is not modern technology

- Does the downpipe have an external wastegate on the pipe? Is it purple? If so, this is likely your entire problem. :thumbsup: Again, a dated piece.

- The ATR double pumper was overkill for a normal car. I've seen cars belch black smoke from having too much fuel from those things.

The boost problem may be due to a stuck or leaking wastegate. As for the rest of the combo, I think it probably just needs updating. This looks like a case where removing parts, plus replacing one or two with better modern ones, and good tuning (with a scan tool!) would help the car and make it perform better.

hplar
06-21-2005, 01:41 PM
Keller,
Thanks for replying. According to ATR the Stage 3A is an 800 CFM turbo. ] ATR says I should have 36lb injectors with that turbo and then have the chip re programed. The wastegate is on the turbo with the rod going to the puck. So whats the deal with the Chip? Should I get a new one or what? Again any help would be great.

Keller
06-21-2005, 07:13 PM
- See http://www.gnttype.org/techarea/pictureguides/turboguide/turbos.html 800 cfm = TA49. Just remember that is what your turbo probably should be called.

- The 7th is definitely not necessary. Remove and put a regular vacuum block in its place.

- Get a set of 36 lbs. injectors to replace the 33's. Which may not flow 33 lbs/hr.

- Pitbull chip can probably be replaced be something else. i.e. Red Amrstrong, Jay Carter, TurboTweak, etc. Or use an updated Pitbull if you wish, matched to the new injectors.

- The downpipe wastegate or actuator may be sticking. Or the system which activates it may have a problem. You may need some help with this one.

- The ATR double pumper could probably be replaced with one more modern pump. i.e. Walbro 340 or Red Armstrong XP. Less power usage and switching, and better fuel control.

That is my opinion. For what it's worth, my car has basically the combination I am describing. A very classic setup.

hplar
06-22-2005, 08:32 AM
Thank you for taking the time. I will definitly use the info. :cheers:

edv2
06-26-2005, 03:05 AM
I had the same problem with my car, ended up being the Atr external wastegate was both stuck closed and had a hole in the diaphram! Good Luck!

Ed V. :)

hplar
07-07-2005, 03:43 PM
That is great because I have a new one on order. I laughed because they are all on back order so it must be a common problem!!

hplar
07-26-2005, 04:06 PM
I put a new wastegate on the car and it made a big difference. It dosent drop as far down and is much quicker to build back up. Is it normal to see some fluxuation in boost in relationship to RPM or shifting?? I am much happier but still would like to see it pin at 18-20 and stay there until I take my foot out of it. Any help would be great

Keller
07-28-2005, 12:40 PM
Shifts likely have some effect. "How much" is the question. And how you have it plumbed will effect it, too. See http://www.gnttype.org/techarea/images/wstgate.gif for a suggestion. Good hoses need to be used, too. Silicone is probably best.

hplar
08-15-2005, 12:52 PM
:banghead:

I took it to the local strip the other night and it only ran in the 14's with all the parts I listed on the thread. The air was terrible but needless to say I was very disappointed. So....I'm taking your advise and buying the 36 lb injectors and taking off the 7th injector. ATR will reprogram the chip for only 30 bucks for the new injectors. Will it make a difference to them if I have a 2500 rpm converter in the car? Should I tell them that for when they program the chip? The car would go halfway down the strip and loose boost and then build it back and pull like hell up top. I want to cry. Hahahaha. It is so frustrating. Any little bit of info helps. I need reassurance im on the right track. Thanks.

Keller
08-15-2005, 02:21 PM
It's concerning that the boost control is still not stable.

I would give them all the info you can about your build. I would also suggest exploring other avenues for chips as a source.

What were your MPH / splits on your passes? Any O2 readings?

hplar
08-16-2005, 02:17 PM
Keller,

this is the way the best run went.

60ft..2.070
330..5.768
1.8..8.592
mph..76.76
1000ft..11.685
1/4..14.006
mph..92.82

This is with the boost fluxuation...enough to drive me nutty. I know it will be in the 13's on a good air night but I still think is should be running a lot better.

Keller
08-16-2005, 05:58 PM
Hate to tell you, but I got high to mid-13s' out of my car with nothing but a chip and a good cool down. (13.6-13.8) No sticky tires, no other pieces removed or added...nothing. Stone stock back in '91 when I bought it used. Similar MPH, though. Perhaps 94. Still, I would expect more.

I'm very curious what your O2 and MAF numbers are. The car may be drowning in fuel with that dual pump setup.

hplar
08-16-2005, 07:07 PM
I know...I ran a 13.8 with my turbo TA with nothig but a chip. I will get the 02 and maf numbers and get back with you. Thanks. :cheers:

hplar
08-26-2005, 05:04 PM
Ok I cleaned the intercooler. It looked like it had not been done in the 18 years of its life. I added the 36# injectors and ATR reprogramed the chip for 30 bucks. When I took off the MAF it just about fell apart in my hand. So We put a new one on. The car runs much better especially at Idle. I STILL HAVE THE BOOST PROBLEM. 02 numberes were right around 810-820.

hplar
08-27-2005, 12:27 PM
Just something else to think about. When I launch it to 3/4 throttle it seems to loose the least amount of boost. When I launch and put it to the floor it fluxuates the most. :nope:

Keller
08-27-2005, 01:31 PM
What MAF was used? A rebuilt AC Delco unit, or something aftermarket? Especially if it is something that necks down with a coke-bottle shape, you are likely not getting 255 at full boost. That would cause your boost to fluctuate. A local owner could barely get one of these to read 200.

I still think the double pump is too much for your car. Having O2s' in the 820's is too rich for max power.