Need some ideas on cause of ping/detonation under boost.

[gsgnnut]

Got a mostly original 87 gn. 76k miles , tt 5.7 chip adjustable waste gate k &n a/f , scanmaster . under spirited acceleration car starts to audibly "ping" / detonation at about 10 pounds boost. I use only 93 /94 octane fuel. Maf is Newer but original style. I have a translater and new style maf not installed as yet and was wondering if the detonation is related to the tt chip and old maf. Fuel pressure and regulator seem to test ok. Haven't done fuel pump yet and its an original. Ideas on what is causing the detonation?

 

[gsgnnut]

I'm thinking it's running lean under boost?

 

[Pronto]

Original fuel pump on its last legs....

 

[ScottHeidinger]

I would start with the fuel pump and a hot wire kit for the fuel pump. I wouldn’t rely on a stock pump even if it wasn’t 30 years old.


Sent from my iPhone using Tapatalk

 

[dank GN]

Okay my first peice of advice is to get a scanmaster or some type of scan tool to see what your motor is doin . After that check your fuel pressure to make sure it’s going up 1lb of boost to 1 lb of fuel . If u hear detonation get out of it . What’s your base fuel pressure?

 

[gsgnnut]

Thanks everyone. I do have a scanmaster, so my next time I step into it Ill have to watch the KR and see what's going on there. I need to recheck FP too but I checked FP and regulator last summer and it was good, 39/40 at idle IIRC but obviously I need to recheck that. I need a new fuel tank anyway so fuel pump upgrade and hotwire and adj FP regulator is long overdue and will be done. I should probably set up an installed FP gauge to monitor that as well. Ill dive into it when i get a free minute and let you all know what I find. I have Cotton's less than 5 miles from my house so I'm sure Ill find my way over there for parts and to pick Jack and Brian's brains. Thanks again

 

[Pronto]

Fuel pressure at idle isn't the question. Can it deliver enough fuel at 10 psi where it starts to knock...

 

[gsgnnut]

Thanks . I understand . Thats why i want to mount fp gauge.

 

[captndave737]

how do you know it's knocking? If it's audible thats really bad. A scan master will show KR when the knock isn't audible. A couple of times my car was running fine but when I refueled it knocked like crazy and would barely run under boost. After burning off the bad fuel and refueling again all was good. Both times i Was on a long road trip.

 

[gsgnnut]

its audible "ping" under acceleration that starts at 10PSI boost. I've been a gearhead my whole life, i know the sound well. I will be watching the scan master the next time I go for a ride in the GN for verification, but I know the sound too well and I know its not good, especially under boost conditions. I was thinking "bad gas" a possibility too because I once put low octane fuel in it when gas was 5 bucks a gallon and damn it pinged bad on that tank if I put my foot in it. I definitely don't make that a habit. I don't trust any gas station not to screw around with fuel grades so that's a possibility that the 93 I paid for may not be as advertised. I did just fuel up too, so I need to check receipts too to make sure I didn't have my head on backwards and goof up at the pump. With a fleet of 7 cars that burn mostly 87, it is possible I just f!@#ed up.

 

[hotairgnx548]

throw some 110 octane gas in to mix with the 87/93 you may have in the tank. keep boost around 15 lbs. set idle fuel at 42psi with vacuum hose off. drive around to mix the gas. then see if does any better . don't nail it yet.

 

[gsgnnut]

Sounds like a good idea. Thanks. Checked last gas receipt shows 92 octane . not the best but not 87.

 

[gsgnnut]

finally got around to doing the diagnostics. Its got anemic fp. 30 psi at idle 37 vac off. fp barely moves with vac on or off. Time for new tank pump and regulator. Thanks everyone for all the pointers. 31 years out of originals can't complain.

 

[Boostrules]

finally got around to doing the diagnostics. Its got anemic fp. 30 psi at idle 37 vac off. fp barely moves with vac on or off. Time for new tank pump and regulator. Thanks everyone for all the pointers. 31 years out of originals can't complain.

Do the Racetronix hot wire kit while you're at it. 31 year old wiring to pump isn't up to the task if you upgrade your pump (which you should).

 

[gsgnnut]

Well I figured out the cause of the detonation/ "pinging" . I did upgrade to the 43# FPR , installed my translator and ls1 MAF, tossed in a new fuel filter and backed off boost a few pounds off the boost actuator but it still had some, but noticeably less pinging, but it ran better than ever. Fast forward to yesterday. Was cruising with Daughter and son in law and had to fuel up so I put in the usual 93 octane. I must have zoned out and put in something other than 93 in the previous tank of fuel (or I got less octane than what I paid for! ) and in any event, With a fresh tank of 93, we did some spirited driving and ping is now gone completely. We did a few hard launches and pulls to confirm. I'm still upgrading the pump and adding a hotwire kit. This GN only has 70 k on her and I did most of the miles and it was never abused so a few more weeks wont hurt. Son in law got a real kick out the performance, horse sneezes and jet whistles and now wants me to help him find him a GN or TR. Love it when a plan come together!

 

[captndave737]

I've gotten a few bad loads of 93 over the years and could barely get on the boost until the tank was gone. I guess there's always a possibility that the truck loaded the wrong stuff into the tank intentionally or not.

 

[Pronto]

It's possible the fuel you got before was bad but more likely you put in some low octain fuel. It's been done before for sure.

 

[RUQWKNF]

At this point, I would recommend adding in a bottle of Techron fuel system cleaner. It will definitely help the situation. And the car will dramatically improve once you get the fuel pump and hot wire kit installed.
With today's E10 blended unleaded fuels, I only trust the big name gas stations. Shell, Chevron, BP and Exxon. Everything else is a game of Russian Roulette. Always 93 as well.

-Patrick-