Truck still backfiring

[shinnlinger]

Hi,
I have a 84 f-600 with a 370 v-8.   It is in the same family as the 429/460. 
I horse traded for it this summer to haul a house I was demoing to the grinder but it's not a bad rig and runs pretty good so I figured I will hold onto her for a bit

Anywho,  I finally replaced the rotted out/ exploded stuck muffler with two turbo mufflers.   Earplugs no longer needed and the cab no longer fills with exhaust.    But if I back off the throttle it will still sound like the guns of navarone and I don't want to blow up the next weakest part of the exhaust system if I can help it.
I got the truck from a guy who had picked it up because it had backfired thru the carb and blew it up.   He basically slapped on another carb just to move it and when I got it it didn't have an air filter.  It does now but it smells rich
It runs fine and for a once a month yard truck I can live with it,  but if it's an easy fix I would like to do that too
Any pointers?
Dave

[beenthere]

Computer? Fuel shut-off solenoid?

[POSTON WIDEHEAD]

My son will be getting his license in a few years.....with all that back firing, he'd want it as is. 

[shelbycharger400]

If the plugs, wires and cap n rotor are good , and it smells rich, it prob is.  Its kinda hard to explain but on the front of the carb at the baseplate their is 2 screws that a flat head will fit in.   
Screw them in and count full turns, but only light pressure!!!!  Most of them should be around  1 1/2 to 2 full turns out from light bottom.

Now when you adjust it, you need a tach on the engine to set the idle to around 600-650 rpm . I do it by ear In a jam.   Then you adjust the screws in or out til it purrs, then turn the screws back in about 1/8 to 1/4 turn, Idle will drop a bit, slight change in idle quality to slight rough. 
Now if you know someone with a 4 or 5 gas analizer you could get it right on the money.
An easy way to get to proper setup is  buy 2 , 4 wire oxygen sensors ($50 ea)  buy the weld in bungs from Jegs , and go to orileys and buy a lean/rich gauge with the 5 leds , their will be 2 sets in it, you only need one gauge and their is directions in it on how to hook it up. I bought 2, I think they are around    One wire gm sensors do work but their not accurate.  3 wire would work as well,  One power, One ground, One sense wire.    4 wire are power, sense wire, and 2 grounds.

equus gauge is $50, and you can hook up 2 sensors to it. and shows 2 seperate patterns.

18 x 1.5 thread is the O2's
jegs weld on bungs are $5
Clamp on no weld  are $38,   bore a hole, clamp on... sounds the way Id go!!   They are the 360 degree seal type too.  I loved those for doin cat converters when at chrysler!  No Leaks!
around 230-250 bux, You KNOW exactly what your doin!
c

[snowstorm]

Computer? Fuel shut-off solenoid?

computer?? in a 1984 truck    nope

[snowstorm]

like shelby says wires plugs cap timeing. if its way rich then its carb problems. holley carb? 2 or 4 barrel.?? holley made a very good carb if it was run without an air filter it may need some attention. dose it have a manual choke?

[shinnlinger]

The wires look good at first glance, not cracked or anything and I have yet to pop the rotor.  Timing was my first thought and adjusting the carb SHelbyCharger style is the second.   As I have said, it runs pretty good so it can't be far off the mark.  I just assumed the previous backfiring was due to the grenaded muffler.  It is a 4 barrel and it may be a Holley.  I don't think it ran long without an air filter.  The guy I bought it from just dropped it on (used) to get the truck running so he could sell it.  It does have a manual choke

I am NOT building a gas analyzer to set up my AG plated yard truck that I run once a month, but someone might and there may very well have someone around here who has one, so thanks for the tip.   Do you mess with the left screw first and then the right or is it hodge podge till it sounds good?  Is the richness the backfiring cause or the timing?  Again it runs good but doesn't start right away (too advanced?) With the flip nose its actually really easy to work on

And NO an 1984 unit does not have a computer....

[SPIKER]

Like mentioned check Carb and Ignition timing, my thought is the Advance is a bit too far ahead.  Check TDC to #1 on the distributor and put a timing light on it.   The Carb adjustment can make it a bit rich which will cause SOME backfiring under reducing RPM braking conditions.   

Not real familiar with the 370's but LOVE the 352/390 351/400 and 460's  8)

Next step is to confirm Cam Timing at TDC and advance springs are all working the correct way, not sure if that one has Mechanical advance or had gone all electronic advance.

Mark
Mark

[shinnlinger]

Thanks Spiker,

You confirmed my thoughts but it has been so long since I have messed with that stuff.  I even have a timing light just have to relearn how to use it.   As far as I know, The 370 is a destroked, debored 460.  It has a 429 crank and a smaller bore.  It is supposedly considered an industrial engine as it is overbuilt.  I believe other than that it is identical to the 460.

Dave

[North River Energy]

If you have a remote-mount hydrovac brake booster, maybe check the plumbing between there and the intake.  I have a pair of cabovers (C600, C750).  Both arrived with identical split mufflers, and both showed damage to the same plastic fitting.

If you have a small vacuum leak, this may account for the carby adjusted rich at idle to compensate, and possibly the lean out (with the higher vacuum) on decel.

If it runs rich to the extent you see black emissions, and assuming a Holley, the power valve diaphragm may have backfire ruptured.

Or not.

[Holmes]

I opened the hood at night on one of my cars and was surprised to see all the  wires and dist. cap sparking.  It's an easy way to check them,they were no good, also spray a mist of water on those parts and see if that makes it run rough.

[snowstorm]

vacuum leak could be some of it also. the 370 and 429 were a real truck motor 460 was used in f250, 350. 352 ,390 same basic block along with a 428. as far as the 351 and 400 being a great motor. depends on what year. 351 clevland yes winsor yup. the 351,400 junk that they made in 77 thu80 no. i bought a new f250 in 84 the first yr of the 351ho. the ho had roller timing chain different cam 4v holley it went real well

[moosehunter]

My recollection of the "FE" block Fords is that the the FE family includes 352-360-390-427-428. The 429 and 460 is a different block. I don't remember where the 370 fell.

mh

[reride82]

Pull a few spark plugs and see if it is running rich. If it is, and I am guessing it is, then I would bet it needs smaller jets. The screws that Shelby mentioned are for idle lean/rich adjustment. The spark plugs always tell the story, they just aren't as quick as O2 sensors.

[shinnlinger]

Well replaced the plugs when I got it home but the old plugs looked pretty good so I guess I'll start with timing. 

[bill m]

I had a bucket truck ,1981 F700 with a 370 4v. Would idle all day long no problem. The back firing on mine was caused be the manual choke not opening all the way sometimes. I would check that first if the plugs looked good.

[snowstorm]

My recollection of the "FE" block Fords is that the the FE family includes 352-360-390-427-428. The 429 and 460 is a different block. I don't remember where the 370 fell.

mh

those are all car or pickup motors. big truck gas= 330  361 391 475 477 534 may have missed one or two. i had a 534 you could find gas enought in 2 towns to run that thing. was in a lt900 5an a 4 trans 1.5 mpg

[snowstorm]

along with the later 370 and 429 i think the last of them were fuel injected

[lumberjack48]

It could very likely be the ignition switch is bad, i had this happen to a couple of my Fords.

Timing being to far advanced is another, or maybe the ignition control module.

[shinnlinger]

MOre info on the truck

Last week I decided to take a pile of scrap to the recyclers vs plowing around it all winter (if we get any snow) and netted a surprising $800! and I had a narrow window to get there from school and when the yard closes and this weekend I got an offer of free logs (most are pretty nice!) I went for it w/out fixing the problem ( I have looked into it a little bit, the choke seems to be fully open,  but couldn't adjust the distributor easily or find the adjusting screws on the Holley carb). I will say that if I feather the gas as I let off I can significantly reduce the backfiring as  does slipping it into neutral from high gear and allowing it to coast down vs downshifting helps as well.   Going down a hill of course I will slow down first and keep it in a lower gear but the brakes are decent in this rig.

I will tackle this problem again someday soon I hope but for now I can live with it as the truck only sees occasional use.  All that said, does this new info help with an interweb diagnosis???
Dave

[swampbuggy]

I don't know if this engine has an A.I.R. pump but if it does on the back of the pump or even remotely is a controller valve. The valve can go bad and it will cause the engine to backfire upon deceleration. Block off the vacuum line to the controller to see if it stops or reduces the backfiring. Swamp

[tractormanNwv]

1968 F-600  330 v8  5spd 2spd
1973 F-700  361 V8  5spd 2spd

We had drilling rigs mounted on both trucks, so they were loaded all the time, both trucks would scare the dickens out of people on the big road, especially running down a grade and easing off the fuel. One time we got in a lawsuit because of the 68 model, running through Charleston, WV with lots of traffic, backed off the fuel and nearly lost the muffler, 2 days later got a call from an Insurance company saying his customer said that a crib timber fell off our rig on the Interstae and hit his car........
But anyways, we had a 74 GMC 366 BBC V-8 5spd 4spd 2spd that never gave any problem, Our 1960 IH B-160 with a 392 IH V-8 5spd 2spd would accaisonally crack a little, but not like the fords.

Jim

[JOE.G]

It sounds as if you don't want to put much money into this truck, What I would do is
1. Tune up and check timing.
2. Adjust carb.
3.Check for exhaust leaks, air getting in will light off any unburnt fuel in the exhaust causing the pop.
4. I would also check for Vac leaks prob do this the same time as tune up.
5.How long is the exhaust, if it is short you may have to extend it a touch.

[Al_Smith]

The 370 was the smallest of the 370,429 and 460 Ford big blocks .It's not an FE engine which stands for Ford-Edsel .

The were compitition for the GMC 366,427 and 455 engines .

About the only thing that will cause a back fire is either a faulty rotor cap or an air leak .If it has a Holley double pumper carb they are known to leak on the power side after a while .

The Holley is a good carb if everything is correct but they can just as big of a nuisance as a GMC quadra jet if something is awry .

Another thing I might make mention of would be the carb base gaskets which can warp a tad bit and leak under the secondaries usually .Trust me they can about drive a person bonkers trying to find an air leak .

[JOE.G]

If the carb is of know back ground, i would buy a rebuild kit, they are not that much and not that hard to do, Holley carb is pretty straight forward, You need to do one step at a time to track down your problem, even though I myself would do them all just so the truck is in good running cond, You can prob do all of the above for fairly cheap.