New guy needing some help, no power 86 305 SWB

[69long bed]

Hi guys, I just picked up a 86 SWB. It apperes to be all stock 305 TBI with smog. I have two differant things going on, Idel goes up and down, and has a major loss of power.And it seems to be using a lot of gas

Any ideas of what to look at or for first?
I have checked for lose wires and vacume leaks, plugs wires all look good.
When its running good it has great acceleration and kick down/passing gear works. When running bad it has no power or acceleration and no kick down or passing gear.

It still has the catalytic converter and all smog equipment.

Thanks in advanvce.

[Corts60]

I may be wrong but I thought '87 was the first year for TBI. If the idle is going up and down and it is TBI, I would maybe check the throttle position sensor.

[69long bed]

I'm new to these trucks so it may not be TBI, but its not a carb.

[69long bed]

Ok so I must have been asleep when looking under the hood. It does have a Q-Jet. and looks to be stock.
Not sure what to look for and check,

Thanks in advance agian.

[Rogue_Alphonse]

If it's a Cali Q-Jet, it'll have a Throttle position sensor on it still. That or the electric choke module is sticking or confused.

As for the loss of power, well... it's like any other carbed engine. Millions of little adjustments, maybe the ignition system, fuel filter... they've proven to me to be a bit more touchy than TBI engines.

[85Bowtie]

You may want to check the condition of your ignition system. I've had similar problems where my truck would be fine one day and crap the next. Turned out it was a problem in the dist. cap (coil button failure)

[69long bed]

Thanks guys, drove it to and from work today. It was about 50/50 split of running good and bad. I will check all the things sugjested. Just wondering has anyone ever had a cat act up, hit and miss like this. So when theres no power I can hold the gas to the floor and nothing changes, no black smoke, no back fire or reving up. I pulled a coupe plugs when I got home they where tan and even burn.

[motornut]

check the vac advance weights in the distributor are loose and swinging,and the hose is on the right spot
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[406 Q-ship]

Originally Posted by motornut

check the vac advance weights in the distributor are loose and swinging,and the hose is on the right spot
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No weights on a computer controled HEI Dist. I would look at cap, rotor, wires, plugs, and all the vacuum hoses. Start with the basics and work deeper.

[69long bed]

Thanks for all in put guys. So I thought I found the problom, I zip tied the choke up almost all the way before i left work. It had a super high idel but it ran great no loss of power. I was thinks that was it. I let it sit for a few hours ran up to the store on the way back it was down on power. Held the gas to the floor and nothing, no power no reving up just nothing.

So can anyone tell me what the vacum / sending units are on the t-stat housing and the other one next to it. both have multiple vacum lines.

One last thing its really bad when cold.
Thanks guys.

[ramz]

Pull one of the spark plugs (#8) and see if its not covered in oil or gas. Mine does the same thing. I have a 86 SWB GMC and its going to shop today to get carb rebuild which prob one of the issues. If you see oil on the spark plugs then the valve seal guides are leaking. Or if has a lot of gas then the carb might need to be rebuilt.

[jdheff1982]

Def. an exhaust restriction. I would have to agree on the cat being bad. Once those cores melt, they will block exhaust passage. Has the truck been running rich? If the cat has been bad, you should have been smelling something like rotten eggs.

Good luck.

[Cue-Ball]

I would say it's NOT the catalytic converter. When they go bad it's not a "sometimes good, sometimes bad" thing. Generally, the engine will run okay at low RPM and consistently worse as RPM increases.

You could be running extremely lean on the left bank, which would cause hotter than normal exhaust. You need to start with the basics. Replace all of the plugs, drive 50 miles, then check them one by one to see which cylinders are running rich/lean. Check all of your vacuum hoses. Check/replace your fuel filter (you may have more than one). Check your distributor cap and rotor and replace if needed. Ohm out all of your ignition wires. Go through ALL of the basics before you jump into anything bigger. Once you check all of that stuff you can check the carb. You might have a stuck needle or a blocked passage. Since you've got a computer controlled carb things are going to get really tricky really quickly. If it were me, I'd throw all that crap away and put in a basic HEI with vacuum and centrifugal advance and pair it with an Edelbrock 1406. Easy peasy.

[kmerrill1993]

could be the smog flapper on the manifold stuck closed

[69long bed]

Thanks for all replies, I have checked and double checked all the vacuum lines. I changed all plugs last night. All 8 plugs had even burn lean color. I always though if a cat was bad it was bad. I have asked a few other buddies about cats they have had experience with cats, that did very similar things. Are there any sensors on these motors that would cause it to run very lean.....

Thanks guys
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[69long bed]

Well I bought put a new Carb on last night plug the vacuum line's and port hooked the distributor advice direct to manifold vacuum. It seemed to idel better but when I put it in gear hold the gas pedal down it losses power and wants to die.

Anyone have any ideas
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[69long bed]

So I just pulled the cap and rotor, the advance unit seems very still. It that right?

Is there a way to check all of that is working correctly?

[Cue-Ball]

Glad to hear you got it fixed! Most of the time it's something simple, which is why I always check the basics when problems like this crop up (timing, vacuum hoses, fuel filters, etc).

[69long bed]

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[69long bed]

Yeah put a new distributor in, and have been driving all week with no problems. Thanks to all of you.
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