hey guys, been a while since I have been on as I am **** broke and havent been able to work on my truck.

something has been bugging me with it though, this annoying gurgling sound when I press down on the accelerator a little more than 1/3 of the way, when I back off it goes away, this happens every single time without fail.
the truck runs great, bad on gas but that hasn't changed since I noticed this.

its a 1985 F150 I6 300 4 spd manual with granny
compression is 140 across all, 160XXX KM

what do you think this is? any other info you need?
thanks

 

How's your coolant level? I had this exact problem with my Maxima a few years ago. My radiator had developed a crack I didn't notice, and I was way low on coolant.

 

Yeah, check your coolant level, you might have some air going through your heater core making that sound. Is the sound in the cab or under the hood?

 

my coolant was good, full to the cap. hard to tell realy where its coming from, I think its more under hood than in cab.

feedback carburetor if that maters at all, no vacuum leaks either.

 

Check your timing. Read your spark plugs. Are you sure it's not detonation youre hearing?

 

plugs are all clean and gaped properly and all fireing. if this is detonation it dosent sound like any I have ever heard from auto class. take water and gurgle it in your mouth, that is the exact sound.

on tuesday I will see if I can check the timing, as that is the next day I have auto class.

 

You don't need auto class to check the timing, and Tuesday is a long way from now.

If you don't have a timing light, most parts stores will loan you one for $20 refundable deposit, or you can usually use it in their parking lot for free.

If you can't get a timing light, you can still adjust the timing by ear. It takes about 5 minutes tops and takes 1 wrench. Use a sharpie marker, mark the position of the distributor on the block. Loosen the bolt on the hold down clamp just a few turns and rotate the distributor counter-clockwise to advance the timing. Just nudge it over a couple of degrees, tighten it down, and start it up and go for a drive. If the noise is still there, rotate it a little bit more. No change? Then try to retard it a few degrees by rotating it the other direction (clockwise) from the original mark you set with the marker. If nothing changes with the noise you're hearing, then the timing might not be the issue and you can rotate the distributor back to the mark you set with the sharpie marker.

Detonation sounds different in every engine.

 

The only thing harder than trying to describe sounds on the Internet is trying to describe color to a blind person.

I'm suspicious of both - anti-freeze in the heater core, and pinging.

To eliminate the heater core as a possibility, remove the two heater hoses from the engine and connect both nipples together with a short piece of hose.

 

The thing about a water cycling through a heater core...is it sounds like a tank of a toilet filling back up. Splishin' and a splashin'. It sounds like water flowing through something and will happen during a free-rev just as much as it would happen while moving. It could be that, but from his description, it's not as likely as detonation/pre-ignition.

He mentioned bad gas mileage. I dunno what he expects from a 300, but 15mpg would be a good day in my experience. Bad gas mileage is a direct result of detonation/pre-ignition. Spark plugs don't always show the signs of detonation because sometimes it only occurs under a load in a certain RPM range and not in the course of everyday driving. The carbon deposits on the spark plug will be burnt off if the engine runs enough after the pinging happens.

You can also eliminate the heater core as a suspect by pinching the heater hoses shut with clamping pliers or find a way to clamp them together pinching off the flow like you would with a garden hose. There isn't much pressure in the heater core system, but do it with the engine off and cold.

Here's a vid. Of course this is a turbocharged car, but you'll hear when the engine runs leans during higher boost, the detonation comes in.
http://www.youtube.com/watch?v=OKVcX...eature=related

 

well it was the heater core, pinched the hoses with vise grips and it went away, so now it is bi passed and the heater core is plugged, will have to see if I can get one from the wreckers. thanks for the help you guys, saves me having to make the trip into town to get the timing checked. I think I will still get it checked in auto just for kicks.

 

I can't imagine you actually need to replace any parts, just burp the air out.

A cooling system flush-n-fill does a really good job of that, it's where you hook a garden hose up to a heater hose and flush the old coolant out the top of the radiator.

 

that sounds simple enough, and would make sense as I wasn't leaking coolant, I will try that right now.