I'm having a odd problem on my motor, and hopefully someone here can help--first, here's the motor/vehicle specs:
-1983 F350
-351W, bored .040"
-302 "RV" cam--not sure of specs, it was in the shortblock when I got it
-Timing currently at 8BTDC, Vac advance is disconnected (caused much pinging)
-302 heads, stock valves, just had the bolt holes enlarged for the 351
-Edelbrock Performer 351W intake
-Holley 600 CFM 4BBL, elec choke, vac secondaries
-Hedmann Hedders, dual exhaust w/no cats
-C6 Transmission, with shift kit
-4.11 Rear end (truck is 2WD)
The Problem:
When the engine is cold, the transmission shifts just fine at high RPM (~5K)--gives that nice, hard shift-kit-shift. But once the engine gets a little warmed up, when you hit the same RPM range, the tranny tries to shift, and the engine seems to hit a "dead spot"--almost acts as if the valves were starting to float or something; it "bucks" a little, but will finally shift if I let out of it just a bit.
Any ideas floating around out there? If you need more info, I'll try and get you what I can.
__________________
Jim
Belpre, OH
91 Bronco EB, 5.8/E4OD/4"/35s
I've heard of problems like this caused by dirt or deposits in the valve body of the trans. I have also heard that some of the cheaper shift kits can cause hang ups between gears. I would suggest getting ahold of the shift kit manufacturor and see what they think.
I would guess modulator. You may want to get a little beefier modulator, I forget what strip color to use, but talk to someone who knows trannies. Also, you may want to try to put the transmission vacuum on a port by itself to see if that helps the shifting.
Why is your vacuum advance disconnected? And I don't think it should cause pinging to have the advance disconnected. Did you plug the vacuum source for your vacuum advance?
Also, would it be possible for the RV cam to have enough lift and duration that you're not creating enough vacuum? The tranny needs the vacuum to work properly.
Why is your vacuum advance disconnected? And I don't think it should cause pinging to have the advance disconnected. Did you plug the vacuum source for your vacuum advance?
Also, would it be possible for the RV cam to have enough lift and duration that you're not creating enough vacuum? The tranny needs the vacuum to work properly.
'82 F150 2WD w/351W (orig 300 I6)
Slik
I guess I better clarify that point--with the vac advance connected, it pulls the advance to approx 60 degrees BTDC at 3500 RPM--causes a whole lot of pinging--by disconnecting it, we limited the total advance to approx 40 deg BTDC--no more pinging.
Oh, and yes--did plug fitting.
Cam is not that radical a grind, a vac gauge reads around 18, so I don't think thats it--the odd thing is this just started recently, but the engine has been in there for 2 years, the trans for 1 year--that's why I'm thinking there might be some validity to the modulator argument--seems like one of those things that could have just failed on me
__________________
Jim
Belpre, OH
91 Bronco EB, 5.8/E4OD/4"/35s
You might want to look into getting an adjustable vacuum advance module. I built a 351 with a lot of the same parts as yours and I also had a pinging problem, usually at part throttle when the engine was fully up to temp. My problem was caused a little too much compression (right at 10:1, but I live at 6000 feet) and I didn't reconnect EGR as the parts on the donner engine was completely useless and I didn't have the cash for new ones.
I did break down and buy an adjustable vacuum advance module. It didn't take a whole lot of adjusting to get the vacuum advance down to were the pinging was gone even on the cheap gas (no, that's not what I run usually!). And I get better fuel economy with the limited vacuum advance than I did with it disconnected or with the distributer retarded.
Roamer makes a good point about the EGR valve. That can cause a lot of vacuum related problems if it does not close properly under acceleration. Also, be careful with measuring total advance under vacuum. The vacuum advance can really only be measured under load which means you would have to rig some way to read your advance while travelling down the road or by using some type of dyno that adds resistance to your drive train. The only problem you should run into without vacuum advance is a drop in gas mileage.
Well, EGR isn't an issue since it's not installed (gotta love the lack of emissions laws in TN) and if I take a hit on gas mileage I'd probably never notice--the beast only gets about 10 as it is.
But I do appreciate all the help--thanks everyone!
__________________
Jim
Belpre, OH
91 Bronco EB, 5.8/E4OD/4"/35s
I agree with the modulator on the trans theory. You may have a hole in the line going to the modulator too. 5K is too high before shifting in my opinion, unless you have it floored, which would give you little manifold vacuum and thus make it shift higher which is the way it's supposed to work.
What I was implying on the EGR (and not doing a great job of stating) is that it does a GREAT job of helping your engine with ping resistance at part throttle by deluding the mixture with burnt exhaust gasses. When you step on it, the EGR valve closes (or it should anyway...) and you are back to pure mixture going into the chamber and not degredation in power. And when you don't have any vacuum (throttle open), there is no vacuum advance anyway, so you don't need it then. As far as emissions devices go, the EGR is one of the best in my books.
[font size="1" color="#FF0000"]LAST EDITED ON 01-Nov-01 AT 10:00*PM (EST)[/font][p]I'll have to disagree with the EGR statement. It does what it is supposed to do as far as bringing down emissions, and most of the time has to be retained legally, but any engine re-tuned to run without egr will run better. The reason you have to make sure it works on a stock engine is because the carb is tuned lean to work with it. If you eliminate the egr without compensation in the amount of fuel the carb delivers, pinging will definitely be the result. But the main reason I don't like it is because it's just something else to go wrong, and given enough time, it will screw up. That's why alot of vehicles have those timers that set the check engine light off, just so you will take it to the dealer where they are SUPPOSED to check the egr among other things to make sure it dtill works.
Make sure your vacuum line to the trans isn't getting weak with heat. My Olds had some clear tubing that when it got hot it collapsed and blocked the vacuum from getting to the trans. I learned the hard way to make sure there is a metal tube or thick vacuum line going that route. My trans eventually burned up. I had noticed it would shift erratically as it heated up, but I didn't think of the tube until I found it when I replaced the trans.
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