[GN138]

Finaly gutted the cat and Holy Cow! What a difference. Problem is, the car seems to be hitting 20psi. I basically have all of the fuel system andelectrical upgrades, stock mechanics and a MAF Translator. What would cause this over boost? There was definately knock under full throttle and one back fire. Running 41-43 psi fuel pressure. I checked the hoses that goe to the wasgate and underside of the turbo and replaced which ones were old and broken looking. Any help or ideas? Thanks!

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87 GN

 

[TWIN86GNS]

GN138,

We told you it would be a big difference! When you said it seems to be hitting 20 lbs of boost, do you have a Good Mechanical boost gauge? If not buy one and install it! Do you have an adjustable wastegate? If you do just back the boost down to about 15 - 16 lbs and try it there. When you were lacking boost did you tighten the rod of the wastegate to try to up your boost? If you did loosen it to get your boost back down.

Glad to hear that your car can make boost once again. Those cat. converters were a real bottle neck to these cars.

Good luck,

Paul Beal
[email protected]

 

[GN138]

Yeah, thanks again! I had an OTC 2000 hooked up to it and there was quite a bit of knock. Only let it do it once and it resulted in a backfire. I don't have the numbers with me now. Getting a good boost gauge after work (hopefully). Stock wastegate, non adjustable, stock chip, new silicone (blue) hoses, Walbro 340 FP, AFPR, hotwire, volt booster, tie down, pinon snubber. All I know is the boost is way too high, like if I unplug the hose to the wastegate and it runs full boost. After that run, I upped my FP 4-5 psi and it still did the same thing. Is there anything I'm missing? I can run WOT until the 1-2 shift and then I have to let off so it will not knock. It pulls like my buddies car did with the stock turbo, thdp and alcohol kit at 24 psi. Feels the same. Thanks for all of the help!

PS: Just found out, I have AC R42 plugs instead of the 43's? Would that make a huge difference? I asked for 43's, but the guy gave me 42's I guess. I know they are gapped at 35 too. Thanks!

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87 GN

[This message has been edited by GN138 (edited January 28, 2002).]

 

[firebird_1252]

how do you read knock on the 2000?

 

[Carolinaturbot6]

Plugs shouldn't matter. Make sure the wastegate hose is hooked up correctly. The straight part of the hose goes to the turbo. The "Y" part goes to the actuator. There supposedly was a bad batch of replacement wastegate hoses sold a while ago. I think the correct size of the orifice in the hose should be between .050-.056"?? Someone needs to verify those sizes for us. HTH

 

[GN138]

My Dad has the OTC 2000 and I'm using it until I get a Scanmaster. It does read knock, although I do not know how accurate it is. I had replaced all of my vaccuum hoses, except for the one going to the wastegate. I replaced that one yesterday along with some others and now it hits 13-14psi and no knock. I'm getting an adj wastegate for free from a friend and a boost gauge soon I hope. Thanks again guys!

Justin

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87 GN

 

[TWIN86GNS]

Justin,

Glad to hear that your car is running better. Get a Good boost gauge on that car ASAP because the stock boost gauges aren't that reliable any more after 15 years.
Once you start upping the boost and monitoring with either the OTC or a Scanmaster you will see what these cars are all about.

Good luck,


Paul Beal
[email protected]

 

[FastwClass]

by GN138:
Gutted Cat results in overboost...

Film at eleven.

Sorry

 

[GN138]

Thanks again! I had a boost gauge, but my buddy needed it more than I did, so I let him have my gauge.

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87 GN

 

[scottyb]

The boost solenoid pulses at a constant rate to control boost. It bleeds off pressure that is intended to push the wastegate open. The ECM does not know what the boost is, and does not compensate for overboost. With a complete stock setup, stock chip, and all working properly the boost is 14.7 lbs. If you make a change like a gutted cat and leave all else the same, then you have less backpressure, more spool and therefore more boost that the ECM/boost solenoid doesn't realize. There are several ways to compensate: race fuel, alky, adjustable wastegate, bleeder valve instead of solenoid, a chip designed for no cat, etc etc. Until you get a handle on it, I suggest plugging the vent nipple on the solenoid to keep boost at about 10 lbs. The risk is not worth it IMO.

 

[Steve Wood]

Just check it for retard with the 2000. If it is not taking timing out, it is okay. As I recall, I gained about a 1 1/2# with the cat off when mine was stock. With the gas these days, that is getting close to the edge on a stock chip with stock timing.

Look for a modern chip for it and that will help.

 

[GN138]

I do have a thrasher chip for it, but it's only 92 oct and last time I used it, it worked for a week and then my SES light blinked on and off. Switched back to my stock chip and everything is well. I'll try the Thrasher again and see what happens. Thanks!

Justin

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87 GN