detonation/pinging problems 400m
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detonation/pinging problems 400m
Hello, New here, but far from new in the message forum world.
about three days ago, I picked up a 78 bronco with a 400m and a c6. I've JUST started to get into it a little, but noticed SEVERE detonation under full throttle. At first, I thought it was just the sound of the flowmasters, but then I saw several others with the same problem on fullsizebronco.com. It sounds like a diesel it's so bad.
I did a good amount of research last night on these motors last night and found that the 351 2v heads used on these motors are quite the garbage, and because of them, the motors are quite prone to detonation, and from what I've heard, is not capable of tuning it out.
so the question goes out to all of you, what's the best way of tuning out the detonation? how far should I retard my timing? any upgrades that can be done on the fairly cheap to help tune it out? will it be necessary to run premium WITH octane booster to get rid of this??
thanks for the help all!
about three days ago, I picked up a 78 bronco with a 400m and a c6. I've JUST started to get into it a little, but noticed SEVERE detonation under full throttle. At first, I thought it was just the sound of the flowmasters, but then I saw several others with the same problem on fullsizebronco.com. It sounds like a diesel it's so bad.
I did a good amount of research last night on these motors last night and found that the 351 2v heads used on these motors are quite the garbage, and because of them, the motors are quite prone to detonation, and from what I've heard, is not capable of tuning it out.
so the question goes out to all of you, what's the best way of tuning out the detonation? how far should I retard my timing? any upgrades that can be done on the fairly cheap to help tune it out? will it be necessary to run premium WITH octane booster to get rid of this??
thanks for the help all!
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First off Welcome to FTE!
second : The 400 is simply a 400 (No M after it)
The 351M is the only M motor.
The 400 was built first
In 1977 The 351M was a de-stroked 400 making it a 351M.
They (engines) are both referred to as the M block...that's all.
I suspect you have removed the EGR from the engine which will cause pinging.
My suggestion: go to the FTE 335 engine series forum where 400 discussion is done.
second : The 400 is simply a 400 (No M after it)
The 351M is the only M motor.
The 400 was built first
In 1977 The 351M was a de-stroked 400 making it a 351M.
They (engines) are both referred to as the M block...that's all.
I suspect you have removed the EGR from the engine which will cause pinging.
My suggestion: go to the FTE 335 engine series forum where 400 discussion is done.
Last edited by Mil1ion; Apr 30, 2007 at 05:02 PM.
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Welcome to FTE!
Dennis already told you, -no M...
Maybe you have read too many Chevy biased hotrod magazines?
Initial timing, sticking advance mechanisms, wrong/mis-tuned advance mechanism, no EGR, carbon deposits...
The heads are OK. They are not as resistant to detonation as the quench chamber design when used with quench or modern swirl combustion heads but they are not garbage either.
The engines can be tuned easily to operate without pinging as long as the compression has not been altered. Many people rebuild with too much compression. Many people think more is better with timing or compression and many other things. -WRONG!
Dennis already told you, -no M...
Maybe you have read too many Chevy biased hotrod magazines?Initial timing, sticking advance mechanisms, wrong/mis-tuned advance mechanism, no EGR, carbon deposits...
The heads are OK. They are not as resistant to detonation as the quench chamber design when used with quench or modern swirl combustion heads but they are not garbage either.
The engines can be tuned easily to operate without pinging as long as the compression has not been altered. Many people rebuild with too much compression. Many people think more is better with timing or compression and many other things. -WRONG!
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wow, ok, my vacuum is all messed up on this beast, and my bronco book is useless. to describe how it's hooked up right now:
my vacuum advance from the dist is going straight into the BACK port of the factory 2bbl carb. (btw I can't feel vacuum coming at of this port at all, is this normal?)
additionally, the pass side of the factory 2bbl carb has a port, and this is hooked into a 3 way valve coming off the upper radiator hose, but nothing else is connected to that. the only other vacuum hooked up is at the throttle cable pod, it's got vacuum going straight into the intake.
I'm trying to decipher that above pic, but not sure what the "pv5" is.
Is this the valve coming off of the upper radiator hose?
I've got three ports coming off of that radiator hose valve, which goes to which, and which goes to the egr?? thanks again in advance, I wish these haynes manuals had a full vacuum diagram in them.
my vacuum advance from the dist is going straight into the BACK port of the factory 2bbl carb. (btw I can't feel vacuum coming at of this port at all, is this normal?)
additionally, the pass side of the factory 2bbl carb has a port, and this is hooked into a 3 way valve coming off the upper radiator hose, but nothing else is connected to that. the only other vacuum hooked up is at the throttle cable pod, it's got vacuum going straight into the intake.
I'm trying to decipher that above pic, but not sure what the "pv5" is.
Is this the valve coming off of the upper radiator hose?
I've got three ports coming off of that radiator hose valve, which goes to which, and which goes to the egr?? thanks again in advance, I wish these haynes manuals had a full vacuum diagram in them.
Last edited by v8only; Apr 30, 2007 at 05:53 PM.
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From: MD
The vacuum routing is incorrect, that's for sure.
Does the Bronco has its original vacuum diagram present? It's under the hood on the driver's side on '79s, not sure on '78s.
Mil1ion has several diagrams where you can correct the routing.
Does the Bronco has its original vacuum diagram present? It's under the hood on the driver's side on '79s, not sure on '78s.
Mil1ion has several diagrams where you can correct the routing.
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For a quick fix you can disconnect the vacuum adv all together, Then time the truck at full mech advance to 38* (you'll have to measure and mark on dampener). I had a hell of a time getting my adv working good, I finally replaced my distributer/vacuum adv pot and bam it was perfect.
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I put up a post in the other section for engines as suggested, but could still use some help here too...I'm using this diagram
http://i69.photobucket.com/albums/i44/ihateminimumwage/351M400x2-1.jpg
however my vacuum is not like that pic exactly. I don't have 4 ports coming off the front of my motor, it's only a 3 valve port coming off of the thermostat housing. one goes to straight vacuum at the manifold, the other two are empty. I also don't have that big solonoid (for the egr?) pass side front of the engine, so I'm not sure I have anything to hook the egr too, can I hook that straight to vacuum, or should I hook it up to the other port on the vacuum tree up front?
http://i69.photobucket.com/albums/i44/ihateminimumwage/351M400x2-1.jpg
however my vacuum is not like that pic exactly. I don't have 4 ports coming off the front of my motor, it's only a 3 valve port coming off of the thermostat housing. one goes to straight vacuum at the manifold, the other two are empty. I also don't have that big solonoid (for the egr?) pass side front of the engine, so I'm not sure I have anything to hook the egr too, can I hook that straight to vacuum, or should I hook it up to the other port on the vacuum tree up front?
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If this is a 78 California Bronco 400 A/T
your calibration code is 8-62T-R10
Don;t use the one you have as the 351M is different.
I'll get you this one I mentioned above if I have it.
your calibration code is 8-62T-R10
Don;t use the one you have as the 351M is different.
I'll get you this one I mentioned above if I have it.
Last edited by Mil1ion; Apr 30, 2007 at 08:09 PM.
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it is a 78 cali bronco, and worthy of mentioning, I was told it was originally a 351m motor until rebuilt, then he built it into a 400 motor. I'm not too worried about having exactly everything factory as far as the vacuum, just as long as somehow I can get the vacuum advance and the egr working properly. Thanks so much!
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Originally Posted by v8only
it is a 78 cali bronco, and worthy of mentioning, I was told it was originally a 351m motor until rebuilt, then he built it into a 400 motor. I'm not too worried about having exactly everything factory as far as the vacuum, just as long as somehow I can get the vacuum advance and the egr working properly. Thanks so much!
Ok, the vac port on the pass side of carb is "timed" port, It gets vac at all times other than idle. This port needs to feed the vac adv pot on the dist and the EGR,However you need the little restricter valves in line for the two Or else the EGR will open too soon and make your engine stumble on excelleration and your vac adv will come too soon.