bronco stutters at 190 +/- (UPDATE)

[green73brc]

(UPDATE AT BOTTOM STILL HAVING PROBLEM)


okay so warmer weather is upon us and yesterday the bronco got up to 190 ish. When it did the bronco would stutter like the timing was off... and miss slightly at idle the harder i accellerated the worse it was... if I got the temp below 190 it would run just fine. I checked my timing that is dead on at 10 degrees... the advance was working and the accelerator pump was doing just fine. Once i got it up to 50 mph or so it would run just fine. It is VERY temp specific I can predict exactl when it will happen just based on the temp needle. I could not determin if it was worse at higher temps since it would only get to 190 ish. Any ideas on what could cause this? Thanks...

I have a stock 302, c4 and 2bbl carb.

 

[Sharkman]

I'll make a guess. How are your fuel lines running in association to your exhaust manifold and pipes. You may be heating up the fule in your lines creating vapor lock.

 

[RangerRob]

This is a long shot, but how are your vacuum lines to the dizzy hooked up? The original lines went through some temp sensing chingadera's (technical term) by the elbow that goes to the heater core from your intake. These routed vacuum differently depending on coolant temps. If you are still running through that but have one side open, it could be messing with your advance.

Mine are bypassed and go from ported vacuum at the carb directly to the dizzy advance.

Like I said, it is a long shot. Worth a look though ?:?

Good Luck

 

[green73brc]

they are guided through that temp block thing... i will grab some longer line and try that out... that is a great idea... as far as my fuel lines... they are routed exactly the same as they always have been... i will check again (and have) for vapor lock.. but the symptoms are directly related to engine temp within a few degrees of being to hot that it occurs...

 

[RangerRob]

Any success with fixing your problem?

 

[green73brc]

Nope no success... i thought I had some success but Yesterday it got so bad that the bronco shut down and did not want to restart There had been a series of start ups and shutdowns.... in 100 ish degree weather. It looked like I had a spark... but it acts like it is missing (to me it feels like) I got it started again after it cooled a bit... i had to put it into low and coast/ 10 mph the 2 miles i was away from home after letting it cool for about 20 mins with the hood up.

So here are the symptoms.... The more I get on the gas the more it will studder. I do not feel the bronco shake but it feels like the timing is off. If I floor it I will kill it. It seems to get worse the hotter it gets (now realize that when running it hits 190 tops but sitting it gets to 200 +/-) It seemed not to be so temp dependent this time. I could not just predict when it was going to happen.

I re-routed my vacumm lines but it sure seems like that did not work... so vapor lock... never had it before but that does not mean i Can not... how can I tell if I have it next time it happens?

 

[rlh1976]

I have had this problem twice 2 diff causes.First if you have a mechanical fuel pump when they get hot you can havr this problem.Second what carb are you running with my old holley the floats were low and at certain temps this would happen till it cooled down.It really sounds fuel related to me.Next time it happens you need to check for fuel and spark.

 

[green73brc]

I have a stock carb... and mech fuel pump.... so it sounds like 2 things could be the problem... vapor lock and spark... but what would cause the spark to die when it gets hot... coil i presume? I checked with the dist and when i fiddled with it i could get a spark at the points....

just tyring to get ideas...

 

[RangerRob]

On the spark side of things, what are you running for ignition (electronic or points)? It is starting to sound like bad points or a bad coil. If you still have points, get some new ones or switch to electronic ignition (Pertronix is easy but so is DuraSpark). Do you have any spares that you can slap on there and test it out?

Good Luck!

 

[green73brc]

stock points and a coil..... i had petronix but went back to points... mabey it is time to switch again... keep the ideas coming... i know we probably can not diagnose it right away but i just want a direction to head

*Edited for content* I dont know why i typed msd ????

 

[74BroncoCO]

Sounds like vapor lock to me. Buy some 1/2" copper tube insulation and wrap your fuel lines wherever you can to try to keep them cool. Maybe install temporary shields between the fuel line and exhaust. Also you might consider a set of Hood vents
The best thing I did to help mine was install an electric fuel pump just in front of the aux. tank. Make sure it's for a carb'ed motor.

J.D.

 

[green73brc]

i just got some 280z hood louvers can i buy this insulation at lowes/home depot?

 

[Cooter_76]

Is there a way to test the MSD box?

Totally different setup, but I had an 89 F150 w/6cyl. that had the same symptoms. Every once in a while it would just die once the engine was warmed-up. After a while it would cool off and run just fine. After weeks of changing fuel pumps & filters, and a lot of "$*%(^"s it turned out to be the ignition module, which would fail once it got hot.

 

[Socal Tom]

Newer fuels boil at about 250 degrees, it's even lower for ARCO gas, and high altitudes. My guess is that when the engine is 190, the carb heats up enough ( check your fuel line routing too) that the fuel in the bowl is boiling. This means that you don't get enough fuel into the jets, and the EB runs lean. The more you open the throttle, the leaner it gets. Mine used to act that way when the engine got to 210, but I had a big hole in the hood. It was worse when I parked it for a few minutes after it got warm.

Try rerouting your fuel lines so they stay away from the radiator hose and the exhaust system, maybe even insulate them. It could also be vapor lock meaning that the boiling is in the lines between the pump and the tank.
Tom

 

[74BroncoCO]

Yes, the insulation is gray in color and comes in 4ft (?) sections. Should only need one, maybe two. Then I just used zip-ties to secure it every 6".

next time, if you're in town and going slow...pop the hood up and let it ride like that and see if you get any problems. I had to wheel like that so it would allow heat to escape. I hope you get to the bottom of it!

Check out this article:
http://groups.msn.com/ATexasOklahomaJeepClub/ouraycotopic.msnw

Also my dad said put in 1/2gal of diesel in each tank with every fill up. I can't remember what it does, but it won't hurt anything either. Replace any old fuel filters also.

J.D.

 

[green73brc]

thanks for the tips and the links... i have stock coil... dont know why i said msd ignition... musta been day dreaming

 

[raharr3]

Mine started acting strange yesterday also (HOT DAY) Temp guage said it never got over 192 though. Hope you figure out what the problem is and let us know. I was down to a couple of gallons of gas so maybe it was one of the causes of my problem. I filled it up today and when I took the gas cap off it almost sucked me in LOL. I have a vented gas cap so I dont know why it had soooo much pressure.

 

[green73brc]

Mine started acting strange yesterday also (HOT DAY) Temp guage said it never got over 192 though. Hope you figure out what the problem is and let us know. I was down to a couple of gallons of gas so maybe it was one of the causes of my problem. I filled it up today and when I took the gas cap off it almost sucked me in LOL. I have a vented gas cap so I dont know why it had soooo much pressure.

Ill let you know what i figure out... i do know the arco gas sucks... i have switched to cheveron for about the past 3 months... mabey it is just me but i like it better... i am going to try and get that insulation tonight and re-route the (aka bend it some) lines and see if that helps.....

 

[74bob]

How old is the fuel pump? I'd go with the others on vapor lock. With the crap for fuel nowdays more and more problems are fuel related. The low fuel tank problem is probably related since the fuel may be getting quite warm in the tank. A cup of water will boil sooner than a quart of water.

 

[green73brc]

How old is the fuel pump? I'd go with the others on vapor lock. With the crap for fuel nowdays more and more problems are fuel related. The low fuel tank problem is probably related since the fuel may be getting quite warm in the tank. A cup of water will boil sooner than a quart of water.

it is about 3 months old (fuel pump)