Hey guys looking for some help here. I have an 85 vette, got some bad gas last year and pulling it out of storage this year had really low gas and barely made it to the station. it has been spitting and sputtering, I put a new fuel filter in it, came back to life 100 percent and by the end of my 30 minute drive it was back sputtering and not firing great, the fuel filter was disgusting and so i thought maybe it got plugged again with crap, put another filter in it and it did the same thing, started running really good then progressively got worse. now when i first go to drive it it goes pretty decent then again get worse as you drive. just looking for some direction and where to turn next. at its worst driving it sputters pretty good pops occasionally but isnt running cleanly at all almost hesitating. i put injector cleaner in twice with 93 octane because i was thinking injectors but have no idea now. please help and thank you!

 

Best thing you can do is pull the fuel pump and sending unit drain the tank and clean it out. Remove the filter clean the lines unhook the fuel rail clean lines. basically clean everything fuel related.

 

if nothing else, check the sock on the fuel pick up tube.

 

Might as well check fuel rail pressure as well, see if the pump is doing okay.

 

hey guys thanks a bunch apparently the fuel pump was done and sock last year?? any other ideas?

 

A LOT of things can happen when you store a car and don't drive it regularly. Me and the other mechanics at work agree that we'd rather have a decent condition 150k mile classic car vs 30k mile classic car. More problems seem to arise from the ones that sit vs the ones that are moderately used. The deterioration of cars when they sit unused is outrageous, and not worth it, IMO. Anyways...

I would seriously look inside the gas tank! gas after it has sat inside a metal tank will leave a residue (brown in color) on the sided of the tank. The residue will INSTANTLY contaminate new gas. Another way to check for this is to smell the gas, if it doesn't smell anything like gas then that's your problem. In that case the tank can be cleaned maybe replaced. Please don't assume the fuel filter is bad, test it. Take your mouth an blow through it, it should flow as free as if the filter wasn't even even in front of your mouth.

One question, What is with the 93 octane? I have an 85 and it does not benefit from that stuff. unless you have a modded engine. I am just curious.

 

I gotcha. yes it was 93,,, there has been a lot of back and forth between 91, 87, 93 octane gas. I do believe the tank is ok as well but willing to try anything.

 

also I bought the car last august and drove it alot... over winter started it every 3-4 weeks. but previous to this the car was sitting for a bit

 

Even with a brand new pump, installed yesterday, have to check the pressure. It may be a bad pump out-of-the-box, or has gone bad, fuel killed it, etc.

 

 

Anything? Goat sacrifice?

I'm guessing you have air so that kinda leaves fuel and spark. It seems like a problem when it goes into closed loop so at that point, check the fuel pressure and the spark quality. It should be a steady blue flame. Are the plug wires leaking? All it takes is a dark garage and a fine mist of water around the plug wires. How is the cap and rotor? When it happens, is the pressure still good and the spark quality still there? Also rap the ECM if it is easily available. I'm not sure for an 85 but in a 91 it is in the engine bay.

 

That is what I have been thinking. If the fuel tank, filter, and pump are fine like you claim then spark would me my go to. Missfires can come and go, trust me I have chased them many times. My guess would be a problem with plug wires. Possible burnt spot some where that grounds out at random times. I'd suppose a spark plug or cap and rotor problems can do it too. It is not exactly easy to diagnose without seeing it in person.

ECM is defiantly not in the engine bay. It should be under the dash on the passenger side. I have not taken the time to look on my 85, but it is the only place I have not been, and I have not seen it anywhere else. It is what I am told, though.

 

Quick update!!! Put regular gas back in the car and it started driving better immediately. I think plugs and wires will be the next thing on the list.... Very strange tho it will change while driving.. at one point today driving it came back 100 percent full power then 5 min later it start stuttering again... keep ideas coming I really appreciate it

 

my friend thats a mechanic says that if it was plugs or wires that it would create a misfire and the check engine light would come on... is this true? no check engine light on...

 

Kinda makes me wonder if you have an electronic issue. One that comes up when the car gets warm. I'd definitely check ignition and fuel

 

gotcha thanks

 

The OBD1 system on the 85 will not flag a specific misfire. It can see irregular readings and set a trouble code (manifold pressure I think), and a misfire can be the cause of that. Some OBDII cars will indicate specific cylinders that misfired, and when the miss last happened.

As for your issue, what the others have said seems right. Check that you have fuel pressure when you are driving, I had to do it by taping the pressure gauge to my windsheild. OReily's sold me a bad fuel pump, which at first just had the car sputter, and after ~3 minutes of dying at idle the pump gave out. If you pulled crud out of the fuel filter, there is a chance that the pump/sock are contaminated as well.
The 'random-ness' of your issue would tend to make me suspect spark over fuel, however. Check the cap/rotor/contacts. Bad wires/plugs could definitely cause this. I have long tube headers, and they would melt my first two sets of wires, so it would run fine when cold and new, then worse and worse as the plug got hot/deteriorated.
It might also be worth checking timing - My girlfriend's 86 would miss at random, and it turned out her dad had the distributor loose when he passed. So when I was working on getting the car running for her again, it would miss some, and backfire/frontfire (in the intake) seemingly at random. Turns out that bumps were changing timing, oops.

Lastly, I'd suspect that a sensor is causing this issue. You'd have a trouble light on if a sensor was way off, so without the light, I think that it would be unlikely that the car misses due to a bad sensor. But, check the MAF sensor to make sure it's wires (the wires inside the tube) are intact, it could cause bucking/missing if it mis-reported. You can clean the MAF as well, dad's F250 will buck unless the MAF is cleaned every oil change or so. He uses brake cleaner.

I hope you manage to fix it! These kinds of issues can be super frustrating.

 

Maybe he can unplug the MAF when it happens? IF it is the MAF, it will default to table values and if it goes away, perhaps that can be the new direction to look?

Why? I would be curious unless he has a K&N and dunks it in oil. That or there is something that gets left behind in the brake cleaner.

 

He can try to unplug the Mass Air Flow sensor, the car will not like that considering that is the sensor the computer uses to determine engine load, but if it runs consistently then that may be it.

A few weeks ago my 85 would start and run fine, but a minute after taking off down the road it would loose almost all its power. Trying to accelerate it would hesitate with some sputtering, but WOT it worked fine. The check engine light came on most of the time claiming MAF circuit High voltage and low voltage. It would idle just fine though.

I highly doubt that it is MAF if it idles misfires at idle. If you want to test if it is a MAF, "borrow" one from the parts store and use it to test the problem. Return the part if it is not fixed. You seem like you are describing a misfire, but I have had people wrongly describe problems to me. Which makes fixing the car harder when it is not doing what they describe. Honestly, it's due to non-mechanics not knowing the lingo of the mechanics.

Can confirm that your car will not throw a code for misfire. Though, as someone mention it may cause other code to be shown that are not the actual problem.

 

Our conclusion on the truck was that is able to pull just enough dirt past the filter that it will get dirty. Could also be that the burnoff system isn't working right. I was hesitant to suggest the brake cleaner cleaning, we use one that is zero residue, but I know some leave a film.

An oily K&N could do it, a friends F-Body blew black smoke out of the tailpipes after 'installing' a K&N. Needless to say, it was oily, and you could trace the oil all the way down into the intake.

Disconnecting the MAF is a good call though, the same F-Body in question ran better with it's MAF unplugged - I imagine that the burnoff + oil didn't treat the MAF very well. OP could give that a try and report back.