detonation at low boost

[ImpalaSam]

Hi, I am the owner of an '86 GN that I have had since '88. It has pretty
much been in storage with limited miles put on it for the last 15 years.
I have tried to keep up with oil changes and added sta-bil to the fuel to
try and prevent any bad issues from the storage. My problem is that when
I do take it out and get into boost the knock box lights up like a christmas
tree at only about 10 psi. If I roll into the throttle and let the boost build
slowly it is not as bad but will still knock. The plugs are fresh. Where is a
good place to start with the diagnosis? I am using an OTC 400oE scan tool.
This was a strong running car back in the early 90's and the combo is the same
so I am guessing it is just something worn or out of spec causing this.

Here is brief description of the car.

1986 GN
55,000 mi.
stock long block
te34 turbo
stock down pipe
true dual exhaust
stock intercooler
hot wired/upgraded fuel pump
green stripe injectors
"street" chip of unknown origin

Thanks

 

[phil_jordan]

That street chip of unknown origin would be the first thing I'd check. Any specs on it? If it's an older, aftermarket chip, the timing could be WAY too much for whatever octane you can find at the pump.

 

[phil_jordan]

And, I'm unfamiliar with that scantool, but if you can't monitor KR or tell if you're running rich or lean, you might want to look into finding another way to monitor what's going on under the hood. Hope this helps

 

[phil_jordan]

Forgot to mention to check ALL of your vacuum lines, and be sure they are up to par. What boost gauge are you running?

 

[ImpalaSam]

Forgot to mention to check ALL of your vacuum lines, and be sure they are up to par. What boost gauge are you running?

I am running an autometer, large liquid filled, not sure of the #

As for the chip, maybe swap back to the stock one for a base line? I am guessing it has a very conservative
timing curve?

On the scan tool, it is an older one used by mechanics, just plugs into the aldl. I purchased a directscan way back, but the PC
I used it with died, I found a Toshiba with W98 but apparantly there is some issue with the Tosh. PC and the configuration of the
port doesn't work. I posted a thread about the adapter that is supposed to make it work but I got no reply, just too old I guess.

I am not trying to make this thing a race car just get it to where I can drive it and have a little fun.

 

[phil_jordan]

Lol. I completely understand about the fun. I'm still trying to get mine dialed in. Most would say to ditch the stock chip as well as the timing in that thing is toward the mid twenties(24 degrees?) and that's still too much for todays gas. With the boost that low, i would trust the stock chip over the unknown so we'd at LEAST know what chip we're working with, ya know?

 

[phil_jordan]

And that sucks about the adapter, because that would be an ideal way to keep up with what's going with the car. Hopefully you get that figured out, or you'll be pressured to buy a scanmaster, because the basic readings could lead us to a lot of unanswered questions. Do you have a vacuum reading on your boost gauge?

 

[TurboTdr3.8]

I would try to pump all the old gas out and start with fresh 93 pump gas and go from there . Todays gas with ethanol last a very short time as compared to the old pure gas .

 

[ImpalaSam]

The gauge I am currently using is boost only, I think I have an old gauge that read vacuum.

 

[krom]

Octane goes away after 2-3 weeks. Drain gas from fuel rail using connector.

 

[626gn]

I would start by eliminating variables. Empty your tank and start with completely fresh fuel and get a modern chip burned for your current combo. The stock chip as well as the unknown 90's chip will do you more harm than good with today's gas. Make these changes and report back if you're still having problems. A working scantool is a must as well.

 

[Chuck Leeper]

Fuel psi is, when this is going on??

 

[TexasT]

I would try to pump all the old gas out and start with fresh 93 pump gas and go from there . Todays gas with ethanol last a very short time as compared to the old pure gas .

X2 just like small engines, fuel injected, boosted engines need fresh fuel. That stabil might keep it fresh enough to run but when you start to "squeeze" it you get detonation.

 

[TurboDave]

Octane goes away after 2-3 weeks. Drain gas from fuel rail using connector.

Any proof of that?
Both of my GN's sit in the garage over winter for at least 3 months or more, and both come out running just as well as when they went in. In fact both my GN's only get driven to cruizin's these days, and seldom get to the gas station for months at a time. Still both run strong!! Not more than a hand full of folks can run 21# of boost on straight 93 octane with no alky as I can.

But I do agree on one thing, as long as his is stored, he needs fresh gas.

 

[ImpalaSam]

Thanks for the replies.

I will start with fresh gas and see if that makes any difference. I've disconnected my FP gauge so I'll
have to get it back out and monitor the FP the see if that is OK.

I'll look into a "modern" chip, the mystery chip was purchased from a local TB club I belonged to
back in the early '90's. Someone had access to a eprom burner and made them cheap. Probably
a copy of one someone purchased. My guess would be an Armstrong chip as they were very popular
then.

 

[Mike T]

In addition to fresh fuel I would replace the fuel filter and have the injectors serviced. This has me thinking about the first chip I bought from BGC in the early 90's called the "street + 10" and I ran it for about 15 years.

 

[ImpalaSam]

I thought about having the injectors cleaned. Is there a preferred source for that?
I live in NE GA, a local source would be convenient.

 

[Mike T]

I thought about having the injectors cleaned. Is there a preferred source for that?
I live in NE GA, a local source would be convenient.

I believe the guy in post # 12 could help.

 

[phil_jordan]

Depending on how much it cost you, I have a set of stock injectors that I removed, had cleaned, and ran perfect before I removed them. Let me know

 

[Ttype6]

I believe the guy in post # 12 could help.

I know the guy in post 12 has given you the most important thing to check first. This is always the first thing to check when you see spark retard. Don't any of you guys think 93 is enough for 10 lbs of boost.