North American Turbocoupe Organization

Full Version: Low RPM knock?
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Hello everyone. Just joined the board and just picked up an extremely nice 1988 Thunderbird Turbo coupe 5 spd. I know very little about these cars, but have a vast knowledge of turbo cars and cars in general. I gotta say I love this car already. But anyways, to the point.

When I roll into the throttle, right before it see's boost I hear the engine knocking, then as boost kicks in, it goes away. It's like the the added 1-2 PSI before it boosts doesn't get read and it either doesn't add enough fuel or doesn't retard the timing. I'm running 92 BP gas in it. The car sat for years and I have run two tankfuls of gas through it.

So, in order to figure out the problem I would like to know how this system works. Does it have a boost sensor on it and does it use that sensor to also retard the timing? Also what exactly does the premium/regular gas toggle switch do?
Hello and welcome.

There is no boost sensor, per se. There is a knock sensor. When it hears knock (within a pre defined frequency range) it tells the EEC it detects knock and the EEC pulls timing. Then timing slowly gets added back until detonation is again heard. If the stock boost control is still in play, then boost will be limited also.

Are we talking knock as in detonation or knock as in rod or main bearing knock? I'm assuming detonation below.

I would suggest you pull the codes and then do a fuel system diagnostics
http://www.turbotbird.com/techinfo/Retri..._codes.htm
http://www.turbotbird.com/techinfo/Fuel_...ostics.htm

Might want to run a can or two of good (techron sp? )injector cleaner through it.

The fuel pump on these cars is barely adequate when new. So it might be a weak link but the diagnostics above should tell what kind of shape it's in.
Thanks for the links Pete, yes I am talking about Pre-detonation. I have an early code scanner, and I did notice a check engine light coming on and off. The previous owner mentioned putting another pump in it, not sure if it was a stock replacement or a 190/255LPH unit. I was going to take a gauge with a long hose, and watch the pressure when I drove to see if it dipped. I guess the FPR diaphram could be stiff and not kicking up fuel pressure until it see's more than a few lbs. It's a 1:1 unit on there isn't it?

I'm going to give it the fuel cleaner treatment, new fuel filter and see what it does. It's under a car cover and will be a few months until I can wrench on it. But thanks for the ideas!
Quote:It's a 1:1 unit on there isn't it?
Yes.