Have something i have never run into prior-when cold under ANY load it backfires

[stlbob]

Now this is odd.When cold any type of load casues an almost constant very small backfires.I felt it before i heard it,had to roll the window and listen.Really robs of power.NOW all that being said as i drive it and it warms up it will still do that DAMN pop-pop-pop-pop .BUT if i go in to lets say the store spend just a few minutes get back in..no backfires and runs super strong..

???????????????????????

i did automotive forever and this has me stumped,it started this right after i screwed with the carb trying to lean it out a bit..SO i put it all back but it is still mad at me..If it was a customers truck id do a coolant combustion test to see if it had popped a head gasket but i know i have not done that..It pops thru the exh ..I had even Seafoamed it a month or so ealier and i was very happy that it did not smoke much at all...

So if anyone has ever run into this please jump in,anyone have an idea of what youd do if it was yours or hell at this point if you have a good joke jion in this thing has really wrecked my sense of humor...

 

[austinado16]

Replace your spark plug with a QUALITY well known brand, and since you're there, replace the plug wires, distributor cap, rotor, and coil wire. You'll be glad you did.

I'll warn you up front. Use only OEM parts.

 

[RThiel]

I wonder if the lifters could be pumping up due to cold, thick oil and holding your valves open just slightly?

 

[87scotty]

Sounds fuel related to me! my sleds just the opposite when its extremly cold runs great when it hits 20 and above it starts over fueling! you require more fuel the colder it gets!

 

[1987 GMC Jimmy]

I had this problem when I first got my Caprice. It'd pop whenever I gave it gas, and it was an absolute dog. It ran really half ass and would act like it wanted to die whenever I'd pull to a stop. It was not a gas problem but an ignition one that replacing the ECM fixed. Yours is TBI so you have the ECM and the ESC module. The way I checked my computer was to pull the codes. Well, the computer didn't even self-test and my SES bulb was good so I pulled the ECM, opened it up, and it was burned. I replaced it with a reman, and it's not had that problem since. I will say that I had first made sure there were no vacuum leaks in the mile long emissions catalyst, and I had done a full tune up of the fuel system and ignition system. See if you're getting any fault codes, make sure you don't have any vacuum leaks, and it would probably be a good idea to do the plugs and check the cap and rotor like the guy above suggests. You can either use smoke from a cigar or cigarette to smoke out the leaks or you can spray an aerosol combustible (i.e. starting fluid). The smoke only work for the stuff connected to the TBI. Pay special attention to the TBI base gasket and the throttle shaft area of the TBI. The throttle arm will be wiggly if needs to have a bushing put in.

 

[1987 GMC Jimmy]

Sounds fuel related to me! my sleds just the opposite when its extremly cold runs great when it hits 20 and above it starts over fueling! you require more fuel the colder it gets!

How are your CTS and O2 sensor? They won't always give you a trouble code when they're bad and replacing them may net some improvement if you haven't done so yet. Vacuum leaks will naturally lean the AFR, but your O2 sensor will compensate for that which can cause that super rich condition. Also, if you can advance your ignition timing a little, that may help, plus inspecting a plug on each bank to see what they look like and clean/replace if needed.

 

[stlbob]

the lifter thing really interests me because when u shut it off i get a quick heat soak and that could explain a few things.To be honest if thats it would be a first for me..i know its not anything to do with computers...lol...should have read my info.

no computer or tbi its a barry grant street demon 750cfm vac sec on a 454 .030 edelbrock manifold and comp cam set up headers Accel and Msd Run only AC Delco plugs.Just did a very serious tune up about 5k ago.BUT you have me thinking going to pull a cple of plugs see how they are burning.

And here is why i think it is something simple,it just came on like from one day to the next.And after i get it warm..then shut it off go do something and fire it back up.NO pop pop pop pop and runs A+

thats the weird part that is making me nuts..i mean wth .dealt with some real odd ball stuff in almost 30 years of doing automotive ..but this , this is going to make me feel like i have done something when i figure this one out.

 

[austinado16]

The reason why I think it's ignition, regardless of when you last put those AC's in there (there are many other components in an ignition system, as you know) is because it's a cold issue only, and you have popping out the exhaust....or at least "think" you have popping out the exhaust.

It is hardest for spark to occur in cold conditions, so any fault in the ignition system will be most pronounced during cold running. I've seen the resistors in spark plugs fail in a way that it seems to delay firing to the point that it's igniting the exhausting gases, creating a pop in the exhaust.

I'm not a fan of aftermarket ignition parts, especially what appears to be crap sold by Accel and MSD. I put an MSD in mine, thinking it would be sooo much better than the original that had 250k on it. The MSD lasted maybe a year, before it started randomly shutting off spark, out on the freeway at 65mph. One minute I'd have a running engine, and the next minute I had dash light on, and the engine was shut down completely. It was impossible to diagnose because it would either light back up and be fine for X amount of time/days/weeks, or if it was so bad I had to pull over, it would start right back up. I finally said to myself, "What's the last thing I did to the engine, and what's not OEM.......The F-ing coil." I threw the original one back on, and the problem went away, permanently. I've since replaced that old coil with a new AC, but kept the old one as a back up.

The reason why I don't think it's something like vacuum leaks, etc. is that those are permanent, and not affect by temperature. Same would go if you had an O2 sensor (which you don't). O2 sensors don't come alive until they get very hot, so they have no effect on cold running.

Since you have a carb, I'd take the air filter off and confirm propper choke function throughout the warm-up cycle. If have proper function, I'd move on to replacing plug wires, cap and rotor, and coil, with OEM, and because plugs are cheap, I'd put a set of plugs in it at the same time.

 

[Rusty Nail]

After it warms, it makes or breaks a sensitive connection.
Wire insulation expanding and contracting, forcing you to make or break a connection.
I have seen this, we covered it on this board?

Hidden, broken wire of the distributor plug.

Anybody remember that thread?
This is duplicated by wiggling those wires.

I don't get paid to throw parts...I actually fix stuff.

 

[stlbob]

Thanks guys , i have a direction to go now and start cking..Going to ck timing also just to ck it i shouldnt be effected by the engine being cold or at temp.Good thought on that electric choke..that HAS been a PITA since new.

 

[stlbob]

OKAY
UPdate it has been in the 70's here..YEP in the middle of winter..and the truck runs hard..no pop pop pop..got cold next 30's ( yeah we have some odd weather) had to warm it up again or pop pop pop...so im thinking fuel now or choke issues..what do you guys think..?

 

[Rusty Nail]

I think cold shrinks the insulation and causes a bad connection at the distributor.

 

[RThiel]

what do your plugs look like?

 

[austinado16]

Doesn't sound like you've actually done any diagnostics and are still just guessing.

 

[Rusty Nail]

lol!