Can’t get over 3800 rpm period 460
#1
04-01-2018, 02:54 AM
Can’t get over 3800 rpm period 460
Hello everyone I have a 1989 Ford F-250 with the 7.5/460 and c6 transmission. I’d like to start off with what’s new on the truck new in tank lift pump, fuel filter ( fuel pressure is about 3 psi lower than spec but still raises 5 psi with the regulator vacuum line disconnected), new distributor, plug wires, spark plugs ( timing was set at 10 degrees), and new four hole fuel injectors. The problem im having with the truck is sluggish performance and primarily it starts popping out of the exhaust mildly at 3k rpm and progressively gets worse until 3800 rpm where it will not wind up any higher, this is an issue because at wide open throttle to shift to the next gear it needs to hit 42-4300 rpm before the the transmission shifts out of passing gear. Over all the truck starts good and doesn’t misfire otherwise, it’s only getting about 6 mpg with 32 inch tires and 4:10 gers driving normally at no more than 55mph
any thoughts on why It starts popping/backfiring at 3k and progressively getting worse until it hits 3800 where it won’t go any higher ? (IT DOES THIS IN GEAR AND IN NEUTRAL)
any thoughts on why It starts popping/backfiring at 3k and progressively getting worse until it hits 3800 where it won’t go any higher ? (IT DOES THIS IN GEAR AND IN NEUTRAL)
#2
04-01-2018, 10:15 AM
Welcome to the site..
Timing was set with the spout removed? Have to ask
With a pressure tester on the rail, what values are you seeing at WOT?
How does it run with more timing advance?
When did the mill start running bad? Prior to all the replacements?
Timing was set with the spout removed? Have to ask
With a pressure tester on the rail, what values are you seeing at WOT?
How does it run with more timing advance?
When did the mill start running bad? Prior to all the replacements?
#3
04-01-2018, 08:31 PM
yes the timing was set with the spout removed
I haven’t checked the fuel pressure at wide open yet because my fuel pressure tester hose is too short to see driving down the road, next weekend I’ll Take a video under hood of the fuel pressure at wide open throttle to see if it starts dropping in the higher rpm. I don’t believe the fuel pressure is dropping because it pops the same way in neutral when reving it up with no load on the engine.
I haven’t advanced the timing yet but will next weekend (I’ll try 12 first then 14 degrees)
i bought the truck a while back with a bad in tank lift pump and the previous owner put the new distributor in a tooth off, so personally I’ve never had the truck running 100% but well enough to drive reliably. The previous owner had only replaced the distributor I have replaced the rest on the list.
(P.s. I had to replace the injectors because because the fuel filter had broken apart on the inside and allowed all that trash into the injectors plugging them up)
#4
04-01-2018, 11:35 PM
Whats the miles on the clock?
That's kinda where I was going,, if the distributor install was off a bit, or if maybe a new timing set was installed prior.
After the blown filter was dropped, the line/rail was flushed? Meaning any chance residual debris was reintroduced into the new injectors. If its popping in neutral on a hard throttle snap, probably not going to exhaust the available volume of fuel without an extended load/demand, pressure may dip a bit, but I like to prove out pressure and volume in a return-to- tank regulated system or rule out what its not before moving ahead. During a misfire, do the vacuum values flatten or fall off? Converter/s?
Was it ever comp tested?
Sounds like the idle is stable/balanced, doubt its a base engine issue (cam/spring etc) but just good to know the base is healthy..
That's kinda where I was going,, if the distributor install was off a bit, or if maybe a new timing set was installed prior.
After the blown filter was dropped, the line/rail was flushed? Meaning any chance residual debris was reintroduced into the new injectors. If its popping in neutral on a hard throttle snap, probably not going to exhaust the available volume of fuel without an extended load/demand, pressure may dip a bit, but I like to prove out pressure and volume in a return-to- tank regulated system or rule out what its not before moving ahead. During a misfire, do the vacuum values flatten or fall off? Converter/s?
Was it ever comp tested?
Sounds like the idle is stable/balanced, doubt its a base engine issue (cam/spring etc) but just good to know the base is healthy..
#5
04-02-2018, 09:48 AM
Whats the miles on the clock?
That's kinda where I was going,, if the distributor install was off a bit, or if maybe a new timing set was installed prior.
After the blown filter was dropped, the line/rail was flushed? Meaning any chance residual debris was reintroduced into the new injectors. If its popping in neutral on a hard throttle snap, probably not going to exhaust the available volume of fuel without an extended load/demand, pressure may dip a bit, but I like to prove out pressure and volume in a return-to- tank regulated system or rule out what its not before moving ahead. During a misfire, do the vacuum values flatten or fall off? Converter?
Was it ever comp tested?
Sounds like the idle is stable/balanced, doubt its a base engine issue (cam/spring etc) but just good to know the base is healthy..
That's kinda where I was going,, if the distributor install was off a bit, or if maybe a new timing set was installed prior.
After the blown filter was dropped, the line/rail was flushed? Meaning any chance residual debris was reintroduced into the new injectors. If its popping in neutral on a hard throttle snap, probably not going to exhaust the available volume of fuel without an extended load/demand, pressure may dip a bit, but I like to prove out pressure and volume in a return-to- tank regulated system or rule out what its not before moving ahead. During a misfire, do the vacuum values flatten or fall off? Converter?
Was it ever comp tested?
Sounds like the idle is stable/balanced, doubt its a base engine issue (cam/spring etc) but just good to know the base is healthy..
yes I flushed the rail, twice actually.
the truck only pops on hard throttle snap if the engine speed reaches 3500 ish otherwise it’s normal.
i can take a video under hood of the vacuum and fuel pressure this weekend for sure
i took the converter off to see if it was plugged up a couple months ago and found that someone had already punched out the core so it was just a hollow shell at that point, right now the exhaust is open at the converter flange
no I haven’t checked compression yet but I can if a fuel pressure test doesn’t reveal a problem and advancing the timing doesn’t help.
Last edited by Archer; 04-02-2018 at 09:55 AM.
#6
04-06-2018, 08:21 PM
So today I bumped the timing up to 15 degrees before top dead center and it definitely made the truck run better, but it still has the issue in the higher rpm
tomorrow I should be able to get vaccum and fuel pressure readings
tomorrow I should be able to get vaccum and fuel pressure readings
#7
04-07-2018, 03:49 PM
Today when I did a vacuum test the idle vaccination was a solid 20 and everything seemed normal until it got into the higher rpm (where I’m having issues) and started getting erratic and bouncing around, from my understanding this is a sign of weak valve springs does this sound correct?
#8
04-08-2018, 10:46 AM
Possibly, but I’d think you’d see an erratic needle at 2k+ or so. So,, the vacuum remains 20ish and stable ‘up to and right at 3800’ then the needle begins the bounce or vib?
I think I’d still comp test it and make sure all the cylinders are fairly balanced. A flat lobe, bent push rod/s or any other components may show up contributing less while cranking, and may cause or aid in a contribution drop out at higher RPMS. Springs can cause a valve float at high RPM, or a combo of failed lobe/spring, push rod could cause reduced perf.
Timing, incorrect gear indexing etc, generally will affect normal reading values, but the continuing exhaust backfire at more top end would seem to indicate a float, valve/hang or? Exhaust restriction would rapidly drop the vacuum value, so that doesn’t seem the case.
But your busted fuel filter pollution keeps coming to mind.
If you can duplicate the misfire stationary, although pretty high RPM’s, have you tried isolating /disabling each cylinder for contribution checks by removing a cap plug wire or injector connector to determine the cylinder dropping out? It sounds like it’s just one, and if so may streamline a point to the cause, or reduce work pulling covers etc looking for possiblities...
I think I’d still comp test it and make sure all the cylinders are fairly balanced. A flat lobe, bent push rod/s or any other components may show up contributing less while cranking, and may cause or aid in a contribution drop out at higher RPMS. Springs can cause a valve float at high RPM, or a combo of failed lobe/spring, push rod could cause reduced perf.
Timing, incorrect gear indexing etc, generally will affect normal reading values, but the continuing exhaust backfire at more top end would seem to indicate a float, valve/hang or? Exhaust restriction would rapidly drop the vacuum value, so that doesn’t seem the case.
But your busted fuel filter pollution keeps coming to mind.
If you can duplicate the misfire stationary, although pretty high RPM’s, have you tried isolating /disabling each cylinder for contribution checks by removing a cap plug wire or injector connector to determine the cylinder dropping out? It sounds like it’s just one, and if so may streamline a point to the cause, or reduce work pulling covers etc looking for possiblities...
#9
04-11-2018, 07:11 AM
The needle on the vacuum gauge starts bouncing at 2900 and progressively gets worse. When I was doing the testing I was giving the truck about 1/2 throttle so it was only pulling about 10 inches of vacuum when the needle started fluttering.
the engine sounds happy below 2900, idles/drives smooth
the engine sounds happy below 2900, idles/drives smooth
Last edited by Archer; 04-11-2018 at 09:20 PM.
#10
04-11-2018, 09:25 PM
Another thing I forgot to mention, when I “beat” on the truck (I.e. get the rpms up high enough to pop) more than 3 (or so) times in succession it picks up a nice lifter knock that goes away after 5-10 more minuets of driving normally.
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