Engine vibrating 3K+ rpm.

Chenn2389

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My new engine (250 miles) recently started vibrating at 3k+ rpms. It does it in gear, in neutral, and in gear with clutch in so its not a drivetrain issue. I checked my timing its at 10* where I set it so I don't think its a spun balancer. I am guessing I am dropping cylinders, or pinging. I can't hear the typical pinging noise over my exhaust note and there is no popping from backfires. I checked my fuel pressure I was running rich. Fuel pressure on the regular was at 48 psi, from when I was running 19# injectors. I currently have new freshly bench tested motorcraft 24# injectors with a bbk maf for 24#. I put the fuel pressure back to 39 which is what my tune was set up for. Didn't change the issue. All my temp sensors, IAC, MAF are new. Throttle body is new. I recently swapped out the IAC for a new one, I used break cleaner to clean the TB, some of it may have gotten into the TPS. Could a bad TPS cause engine to misfire/ping at higher rpms? I am going to check the voltage on that tonight. The IAC and TPS were the only thing that potentially changed. Anyone else have any other ideas or things I could check?
 
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07GtS197

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Is your car tuned for those injectors? Testing fuel pressure only at idle isn’t the best test, you’ll need to rev it to see where it’s at in the upper rpms or better yet keep the tester attached and drive with it so you can watch it under load.


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Chenn2389

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Is your car tuned for those injectors? Testing fuel pressure only at idle isn’t the best test, you’ll need to rev it to see where it’s at in the upper rpms or better yet keep the tester attached and drive with it so you can watch it under load.


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yes it is tuned for it. I didn't reset the FPR when I initially installed it.
 

skidoo

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That's a good idea, idk how accurate my cheap laser thermometer is but I will give it a shot.
Try it at different engine speeds, you're looking for a difference of more than 70 degrees, so doesn't have to be extremely accurate. Won't be as accurate as a thermocouple, but should show any glaring problems. Are the rocker arms adjustable or just bolt down pedestal style? Tight lifter could cause a misfire.

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Chenn2389

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Try it at different engine speeds, you're looking for a difference of more than 70 degrees, so doesn't have to be extremely accurate. Won't be as accurate as a thermocouple, but should show any glaring problems. Are the rocker arms adjustable or just bolt down pedestal style? Tight lifter could cause a misfire.

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They are crane 1.6 full roller pedestal mount. Fresh edelbrock performer heads. I want to rule out the fuel and electronics before I take top end apart and need to buy all the gaskets.
 

Chenn2389

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I tested the TPS. 1.0v at idle, 4.7v at WOT and a nice leaner curve from idle to WOT with no dead spots or spots that hang. I’m seriously lost.
 

Chenn2389

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I started it without the accessory belt to rule out any of the pulleys. It’s definitely misfiring. It’s idling like shit and car is shaking. Is there a way to test the coil and plug wires? I can’t narrow it down to which cylinder today. My IR thermometer batteries dead go figure.

I don’t really wanna just throw more parts at it.
 

ttocs

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checking for bad plug wires can be as simple as grabbing the wires while its running and waiting to get shocked or by listening for a ticking noise that is made when it arcs. Its also not a great way to look if it does not happen to be a bad wire but if you have a bad wire and unplug it the motor will not change as much as if its a good wire/plug. The final and craziest, I mean the safest way to check is with a mulitmeter
 

skidoo

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I started it without the accessory belt to rule out any of the pulleys. It’s definitely misfiring. It’s idling like shit and car is shaking. Is there a way to test the coil and plug wires? I can’t narrow it down to which cylinder today. My IR thermometer batteries dead go figure.

I don’t really wanna just throw more parts at it.
Check compression on all 8 cylinders? Did you double check the firing order? Standard 302 and HO use a different firing order. You can briefly touch each header tube as it's warming up from dead cold or spit on each tube. If the cylinder is not firing at all, it'll be cold. Or like was mentioned, pull individual plug wires off as it's running one at a time. Listen for no change and that's your dead cylinder. Then you can swap plugs, injectors, wires with a known good cylinder and see if the dead cylinder follows the plug, injector or wire. If it doesn't then check the wiring harness with a noid light in the injector harness. If that's good then it's mechanical. Rocker arm, valve spring, pushrod bent.

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Chenn2389

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Check compression on all 8 cylinders? Did you double check the firing order? Standard 302 and HO use a different firing order. You can briefly touch each header tube as it's warming up from dead cold or spit on each tube. If the cylinder is not firing at all, it'll be cold. Or like was mentioned, pull individual plug wires off as it's running one at a time. Listen for no change and that's your dead cylinder. Then you can swap plugs, injectors, wires with a known good cylinder and see if the dead cylinder follows the plug, injector or wire. If it doesn't then check the wiring harness with a noid light in the injector harness. If that's good then it's mechanical. Rocker arm, valve spring, pushrod bent.

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The fire order is correct I checked that. I haven't done a compression test yet. I will try the noid light thing this weekend, can you rent those at the part store? I did unplug the MAF last night and the car died immediately, not sure if that's normal. Is there a way to test a MAF? Its brand new I have a hard time believing it shit itself after 200 miles. I had the injectors flow/bench tested and and put new o-rings on prior to installing them too. The fuel filter is new and new diaphragm on the fuel pump. I have a hard time believing they clogged up on me in that short distance as well. Wouldn't a bad spring, loose rocker, or a bent pushrod make a shitload of noise?
 

Chenn2389

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I put my timing light on all of the plug wires, and I noticed a few of them would barely blink and be super dim weak blinks, but others were nice and strong. Ordered a new cap, coil and plug wires. Does the MSD HEI cap come with a rotor? I didn't see any replacement rotors.
 

Wmac

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If you are referring to MSD kit #8482, it does indeed include a rotor.

In one of your posts, you mentioned installing a DUI coil and distributor. If you do have an intermittent high rpm misfire and the new plug wires don't help, try the stock coil and dizzy if you still have them.

The oem coil and distributor (guts) are far superior to any aftermarket. And don't rule out the BBK mass air meter as a source of your issue.
 

Chenn2389

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I noticed at the same time I got vibrations/misfires my instrument lights stopped working. Well I pulled the cluster and the dimmer switch and found the plug burned up. You think this short would be significant enough to give me ignition problems??D8F9D3CD-2C35-40C7-B738-C803C2934DD3.jpeg
 

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