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1983 G20 Van Pre-Ignition, baby won't die
#769378 January 06th 2021 1:22 pm
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Hey!

My van was a barn find. I bought it with carb issues and took it to a shop to get the carburetor rebuilt. 

The van was used in a stunt in a movie (an independent film so there's no insurance or anything for this) and there was a small, but very real, fire in the dog house. 

After the fire I started having pre-ignition problems. This thing won't shut off. I read online that if I kill it in gear that could be a temporary fix, but if I let the van idle for any significant amount of time it will take anywhere for 2-5 minutes to die after I kill the ignition. 

Any suggestions of where I should look first? 

I'm far from an expert (see: lit my van on fire stupid), but my suspicions are
1. When the van was sitting in the barn and occasionally running on 6 out of 8 cylinders that there was carbon build up and now that my carb is rebuilt, it's firing on all cylinders and the carbon is causing detonation.
2. The electrical/computer run choke is acting up, or
3. The fire messed with a vacuum line. 
4. Maybe the shop tuned the idle too high and my air/gas mixture is off

Where should I look first? I'm trying to not spend any more money at the shop...

 

Re: 1983 G20 Van Pre-Ignition, baby won't die
Olivia #769381 January 06th 2021 1:50 pm
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The shop may have set the idle tooooo high just to keep it running and thus able to charge you for work that had nothing to with whats really wrong ..........

Id do a trace and replace the wiring and Vac lines.

Dont take it back to that shop ! Let me guess they charged you $600 ...


SUNSHINE VANS-VAN DIEGO
ADRENALIN BY THE GALLON & CHASIN RACIN
ONE FOR THE DIRT & ONE FOR THE STREETS
'93 CHEVY G30 454 4X4 SPORTVAN EXT 146" WB
'92 CHEVY G30 454 BEAUVILLE EXT 146" WB
Re: 1983 G20 Van Pre-Ignition, baby won't die
Olivia #769382 January 06th 2021 2:51 pm
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2-5 minutes of run on sounds preposterous, I’ve never seen more than a few seconds. Not knowing what this fire entailed, I’d be checking electrical. Make sure the ignition switch is allowed to do its job, and chasing any damaged or poorly replaced wiring.

Re: 1983 G20 Van Pre-Ignition, baby won't die
Olivia #769384 January 06th 2021 3:27 pm
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Yeah my dad and I went to work on it over the holiday. I think it was parked and idling for 15 minutes cuz it was super cold out and we wanted to run the heat while we messed around with the interior. I shut the van off in gear sort of anticipating pre-ignition and it just kept going, it felt like forever.

Should I take it to a shop or try to DIY it?

Re: 1983 G20 Van Pre-Ignition, baby won't die
Olivia #769386 January 06th 2021 4:27 pm
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I've never witnessed dieseling occuring that long after key shut off...The carb must be leaking or there is just tons of fuel left in the intake.

Find someone who can work on a carb using logic and experience, rather than bravado while watching that clock spin.

Also look into a water decarbonization, knowing that hydrolocking, and a destroyed engine is a possibility if done incorrectly.

Fuel system cleaners with PolyEtherAmines are said to be best at decarboning the cylinder heads.
redline sI1 and
Gumout regane
Crc Guaranteed to pass are just three
FCS's which contain PEA

Re: 1983 G20 Van Pre-Ignition, baby won't die
Olivia #769390 January 06th 2021 6:29 pm
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Preignition is Pre, theoretically firing horribly out of time, should be a poor idle and not the healthiest thing for engines. I don’t know how shut down in gear could be helpful, aside from stalling it if it’s manual. I’ve never heard of it going on that long. Is it a rough idle or normal? Verify it’s not getting spark with key off.

DIY can cost much much less, but throwing parts at it, breaking plenty during and getting no where can add up also(no guarantee a mechanic won’t do this at their own rates).

A keen eye properly fixing everything obviously fire damaged is a start. A volt meter to make sure everything is working as intended. Inspecting plugs/wires/vacuum leaks. A shop will have to chase the basics before digging deeper, worth a shot.

Re: 1983 G20 Van Pre-Ignition, baby won't die
Olivia #769391 January 06th 2021 6:49 pm
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Still trace and replace the wiring after a fire is a MUST ... next is switches and melted vac lines ... set the timing to factory spec and tune from there.


SUNSHINE VANS-VAN DIEGO
ADRENALIN BY THE GALLON & CHASIN RACIN
ONE FOR THE DIRT & ONE FOR THE STREETS
'93 CHEVY G30 454 4X4 SPORTVAN EXT 146" WB
'92 CHEVY G30 454 BEAUVILLE EXT 146" WB
Re: 1983 G20 Van Pre-Ignition, baby won't die
Olivia #769393 January 06th 2021 7:42 pm
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When the van is on the idle is normal. After it has been idling for a while I turn key off, no more spark, and then it sputters, shakes, occasionally backfires. Not pretty.

Re: 1983 G20 Van Pre-Ignition, baby won't die
Olivia #769395 January 06th 2021 9:00 pm
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That is a carbon build up thats still hot enough to ignite the gas ... its called dieseling

https://www.howacarworks.com/ignition-system/curing-running-on

Letting the van idle for long times can cause this problem as the burn is not the most efficient in idle. Thus not burning all the carbon out of the system. Take it out on the freeway and romp on it to clear out all that carbon.


SUNSHINE VANS-VAN DIEGO
ADRENALIN BY THE GALLON & CHASIN RACIN
ONE FOR THE DIRT & ONE FOR THE STREETS
'93 CHEVY G30 454 4X4 SPORTVAN EXT 146" WB
'92 CHEVY G30 454 BEAUVILLE EXT 146" WB

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