I've got an 86 IROC-Z with an LG-4 motor. Lately it seems like the engine's falling apart on me. I'm trying to determine what's wrong...many of these may be unrelated but I'm gonna try to relay the events in the order they happened.

First thing I noticed was a knocking sound, like someone was tapping on the firewall. It usually happened on damp or rainy days and went away after the engine warmed up. It wasn't like it was all the time either, just between 2000 and 2500 rpm. I thought it may just be a worn component somewhere, so I didn't think much of it.

Then the weather turned cold and I started having problems with the engine stalling or theatening to stall. I'll be driving and it'll suddenly lose power and sometimes it stalls out completely, but most of the time it just sputters extensively. I thought at first it might be carburetor icing or a bad batch of gas, but I'm not really sure. Even when it stalls I can start it right back up and if I pull over before it stalls I can rev it back to life. I added some Prestone Winter Gas Treatment to the tank.

Now I'm not sure if it's the Winter Gas Treatment breaking up ages of carbon on the intake valves or something unrelated, but most recently the engine has been running more and more roughly. It also occasionally spits black carbon deposits from the tailpipes. Someone suggested it may be an ignition problem so I changed the ignition coil, cap and rotor on the distributor, but the distributor was loose and now my timing's off...I'm starting to wonder if that was the problem in the first place...my distributor coming loose and the timing being out of whack. Could this have caused the above problems? I'm re-timing it tomorrow.

What I'm asking is if these particular symptoms are indications of one common problem, such as the timing being off, a cylinder not getting spark, a stuck valve, a bad batch of gas...WHAT? Or are they most likely unrelated, separate problems? Anyone have any experience here? This car's my only means of transportation, so it's imperative that I get it running properly again. I would appreciate any tips, ideas, words of encouragement...

Thanks in advance.
Mark

 

Sounds like the needle valve in your carb has some trash in it, or your float has quit being a float and is now a sink. Either way, it's time for a carb rebuild.

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"So many Mustangs, so little time..."

 

I had the carb rebuilt last winter. Choke pull-off was broken and it was fouling plugs. Do you think it would've gone up that soon?

Mark

 

Tree Rat,

It sounds like the mix is WAY too rich if you're getting carbon chunks out of the tailpipes. Depending upon how the carb was rebuilt, you may have to do some adjustment to the mixture control solenoid and TPS. This, os course, is after you verify that the float level is correct, the inlet needle and seat are sealing properly, and the choke is operating correctly.

Even though the carb may have been completely rebuilt and adjusted a year ago, it might require adjustment again. It's fairly easy to check without disassembling anything except the air cleaner.

Oh. The "knocking sound" could be any number of things. If it happens continuously and varies with engine speed until the engine is warmed, you might have an oil pressure problem, worn components, or a leaky exhaust flange. If the sound only occurs on accelleration, it might have been a detonation problem, but that usually only gets worse as the engine warms up.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0

 

Check the choke pull-off to see if it is out of adjustment. Also make sure your choke stove is heating up.

 

OK I'm gonna re-time the car tomorow...now I haven't done much work on carbs...I need to know how I would check to see if there's a float problem and how to adjust the choke pull-off.

As far as the heat stove...the THERMAC door that closes off the intake snorkel and opens to the heat riser is definitely working...problem is there's an Early Fuel Evaporation actuator on my exhaust manifold that is for some reason not hooked up to vacuum like it should be according to my trusty Chilton manual...would this make the difference? If so, can anyone tell me what vacuum source the EFE hooks up to? I don't see any open vacuum lines on the carb.

Also, does it sound like I might have one cylinder somewhere fouled out...something wrong with the ignition, or is this definitely looking in the wrong place given the symptoms?

Appreciate it once again.

Tree Rat???!

Mark

 

Tree Rat??? OMG, that's too damn funny Vader. LMFAO!



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89RS w/350 TPI; 69RS/SS w/450 HP 350/Muncie 4-Speed "Too weird to live, too rare to die."

 

OK...got the timing right...seems to have fixed the vibration...also reassured to know my ECM is working...light came on when I unplugged the distributor wires...still sounds like one cylinder's missing...should I (*ack*) pull the plugs? Also, how would I check the calibration of the choke pull-off and the idle mix?

thanks
Mark

 

Sorry I was not clear. When refering to the choke stove. I was describing the electrical coil on the side of the carb that heats up the spring for the choke to open. This should heat up within minutes of the car starting.

As far as the choke pull-off it should open the butterfly plate about 1/4 of an inch and should drop the fast idle cam 1 step.

For the miss I would also make sure cyls 5 and 7 are not out of order. If you had more than one wire off it can be easy to get these two mixed up.


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91 Formula 305 TPI Stock
88 Formula 350 TPI Stock

 

OK...choke pull-off is working, choke is opening 1/4" on startup. Engine still runs a little rough when cold...guess this is to be expected this time of year. Also, all wires are going to the right plugs...my dumb *** thought that the cylinders were numbered 1-2-3-4 down one side and 5-6-7-8 down the other, so I was standing there for a good 15 mins wondering "How is this thing even running?" Might have a plug carbon-fouled...not sure, but it ran alright yesterday...I don't think the needles are stuck open to the floats cuz the fuel pump stops when I turn the ignition on before I start up...any other tips?

Thanks again for all your help...
Tree Rat

 

On a follow-up note...no more black carbon spitting from the tailpipe, but a lot of moisture...think it's water, doesn't smell like gas. Isn't that normal in winter when the engine's cold, though?

Squirrels
Mark

 

Water out of the back is good provided it is not antifreeze from a craked head or bad head gasket. Water is a by-product of good combustion. The colder air causes the gasses to condense. Hence, water from the exhaust.

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91 Formula 305 TPI Stock
88 Formula 350 TPI Stock

 

Alright...POS stalled out on me again...luckily it was close to home and I got it started back up. I think it's the cold weather, but it's warmed up now and it still doesn't sound quite healthy. Where do I look next, the carb?

Mark