Timing Question
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5th Wheeling
Joined: Dec 2008
Posts: 34
Likes: 1
Timing Question
A little background...I have a 1991 F150, 4.9 inline 6 with a hesitation problem. I had previous codes for EGR problems and found that the EGR valve was stuck. I fixed this and now I'm getting 111 (system pass) codes now. When I slam the gas from a dead stop, the truck hesitates, sucks air, and sometimes backfires thru the intake. At highway speeds everything seems ok, until I need to pass someone and then I still get a hesitation.
So here's my question. How much can I advance my timing? I tried setting it at 14 degrees BTDC but I still get the hesitation. I know it's ridiculous, but when I advanced it to 20 BTDC, the truck responded beautifully and I didn't get any pinging at highway speeds. Is it safe to leave it this far advanced?
Recent tune up including new plugs, fuel filter, PCV valve, air filter and breather. Vacuum lines are fine, cylinder compression was within specs, fuel pressure was within specs. I pulled each injector, cleaned them, and replaced o-rings, filter, spacers, and pintle caps.
Does anyone know what else could be causing my hesitation problem?? I would really appreciate any help. Thanks.
Darren
So here's my question. How much can I advance my timing? I tried setting it at 14 degrees BTDC but I still get the hesitation. I know it's ridiculous, but when I advanced it to 20 BTDC, the truck responded beautifully and I didn't get any pinging at highway speeds. Is it safe to leave it this far advanced?
Recent tune up including new plugs, fuel filter, PCV valve, air filter and breather. Vacuum lines are fine, cylinder compression was within specs, fuel pressure was within specs. I pulled each injector, cleaned them, and replaced o-rings, filter, spacers, and pintle caps.
Does anyone know what else could be causing my hesitation problem?? I would really appreciate any help. Thanks.
Darren
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Joined: Mar 2002
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From: Bonita Springs FL
+1 on disconnecting the SPOUT first. Your "base timing" of 20 BTDC will certainly cause huge problems. Either you left the SPOUT in while setting the timing (did you notice the pointer bouncing around while you were trying to set it?) or the balancer is spun, making the pointer useless.
Lead Driver
Joined: Nov 2002
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From: Concord, NC
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5th Wheeling
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Thanks for that information. I've never been under the timing cover, so I wasn't aware the 300 used only timing gears. So, do you have any other ideas of what could be causing my hesitation issue? The only thing I haven't replaced was the coil. It's still origiinal on the truck? Could this be causing the problems? Also what about something with the exhaust system? Thanks.
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What is the condition of the thermactor system(air injection)? The lines and valves can develop cracks and rust holes which tend to create a lean burn problem, and that shows up as a stumble under load.
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5th Wheeling
Joined: Dec 2008
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Thanks. Haven't checked that yet. Time to bust out the Haynes manual again. 
Would a problem in the thermactor system normally throw a code, because I'm not getting any codes right now? I appreciate all the help!
Would a problem in the thermactor system normally throw a code, because I'm not getting any codes right now? I appreciate all the help!
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5th Wheeling
Joined: Dec 2008
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Yeah, I've been running fuel injector cleaner in the gas tank, but I did one better than that. I pulled each injector out, soaked them in injector cleaner overnight. Then I blew out all the gunk with an air compressor and throttle body cleaner. Also, replaced the filters, o-rings, and pintle caps. When I tested them in my harness, they seemed to show a good spray pattern.
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5th Wheeling
Joined: Dec 2008
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Quick update Conanski: I checked the thermactor system and it all checks out. I'm getting air flow from the smog pump and also getting flow after the air bypass/diverter valve. Flow increases as I increase the engine RPMs. The vacuum line going to the air bypass/diverter valve are functioning also.
I also checked the primary and secondary winding resistance on the coil and they were 0.9 ohms and 9.5 Kohms, respectively, which is within specs.
I'm at a loss...help!
I also checked the primary and secondary winding resistance on the coil and they were 0.9 ohms and 9.5 Kohms, respectively, which is within specs.
I'm at a loss...help!
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5th Wheeling
Joined: Dec 2008
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Well, I wouldn't say completely useless. I am ruling things out (ignition coil and thermactor system), which is helpful. No, I haven't checked the harmonic balancer yet. I'm waiting for some help to do that (mostly to get the belt back on), so I'll probably do it Friday. What's the best way to tell my #1 piston is a TDC? When I crank the engine by hand, is it okay to turn it both directions or should I only spin it the correct way?