Misfire when revving, but not at idle

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ToeKnee805
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Misfire when revving, but not at idle

Postby ToeKnee805 » Thu Mar 05, 2015 10:49 pm

So the car has a recently rebuilt (by previous owner) engine. When i received it it had 0 compression due to the Exhaust cam being 180* off. I re-timed the camshafts and it fired right up. The car idles perfectly and is timed at 10BTDC.

Heres the problem when i go to rev the engine with anything more than super light throttle the car starts to misfire. And possibly even backfire? I can hear the misfire coming out of the intake tubing and the exhaust. It sounds like a muffled machine gun. Kinda like when you try to rev a motor that isnt timed and it starts to stumble the more you rev it.

Ignition Timing 10BTDC
Cam Timing: All 3 timing marks line up
Replaced TPS
Replaced Coil/Igniter
Replaced Dizzy, Dizzy Cap, Rotor
Replaced Wire-set
Replaced and Gapped Plugs
Replaced ECU
EGR Has been removed (misfired when it had the EGR)
1-3-4-2 Firing order on wires

The only thing i have not tried is replacing the AFM because i dont have a spare, and removing the cat to see if the exhaust is clogged. Theres is also no registered codes. I tried seeing if maybe the injectors plugs where on wrong and they arent. If i unplug a spark plug wire it will miss worse, same if i remove an injector plug. I do notice that the resistor box doesnt seem to get hot (im not sure if its supposed to get hot to the touch) The exhaust manifold does have a small hairline crack, but i dont think thats the culprit. The only vacuum lines i still run are TVIS, Small Green valve next to AFM, and FPR. If i unplug the AFM the car dies. If i unplug TPS it seems like nothing happens. I am stumped guys, and im not sure where to go from here. Any help is appreciated.
1986 Corolla GT-S -- Unmolested -- Now Resto Project
1985 Corolla GT-S -- Turbo Levin Track Car
1982 Corolla 1.8 -- Sitting collecting dust

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allencr
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Re: Misfire when revving, but not at idle

Postby allencr » Thu Mar 05, 2015 11:20 pm

What's the compression?
Same equal effect on all 4 when removing a plug wire or EFI?
Pinch off the FPR's return hose to see if more fuel pres. will make a significant difference.
Move the distrib. back & forth to see its effect, ignore the pully timing marks.

totta crolla
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Re: Misfire when revving, but not at idle

Postby totta crolla » Fri Mar 06, 2015 2:51 am

Does the ignition timing change much when you rev the engine ?
10 degrees BTDC is the timing setting with the diagnostic shorted and it should be around 16 degrees BTDC at idle without it shorted.

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Re: Misfire when revving, but not at idle

Postby yoshimitsuspeed » Fri Mar 06, 2015 6:37 am

Time to break out the FSM and start going through the troubleshooting and diagnostics.

Do all their suggested tests for missing and related issues.
Test AFM, TPS, fuel pressure and anything else the book suggests.
Check compression. This will tell you if there was anything wrong with the rebuild and should also confirm your cam timing is correct.
You said you unplugged a spark plug but have you done so on each cylinder? If so did the idle drop the same amount on each cylinder?

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ToeKnee805
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Re: Misfire when revving, but not at idle

Postby ToeKnee805 » Fri Mar 06, 2015 9:05 am

Yessir it misses equally on all 4 cylinder if I remove an injector or a plug wire.
My timing is at 10btdc shorted and 16btdc non shorted.

Haven't tried pinching the return, testing the AFM, or a compression test. I think that's where I'm headed next. I'll post results as soon as I get them in!
1986 Corolla GT-S -- Unmolested -- Now Resto Project
1985 Corolla GT-S -- Turbo Levin Track Car
1982 Corolla 1.8 -- Sitting collecting dust

allencr
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Re: Misfire when revving, but not at idle

Postby allencr » Fri Mar 06, 2015 9:32 am

ToeKnee805 wrote:...equally on all 4 cylinder...


OK, then don't bother with a compression test yet, just move the distributor.

yoshimitsuspeed
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Re: Misfire when revving, but not at idle

Postby yoshimitsuspeed » Fri Mar 06, 2015 11:20 am

allencr wrote:
ToeKnee805 wrote:...equally on all 4 cylinder...


OK, then don't bother with a compression test yet, just move the distributor.


A compression test will still help confirm cam timing is correct or not and tell overall system health.
Hell the previous owner could have done something stupid like install GZE pistons with a 2mm HG or could have adjusted all the valves too tight or who knows.

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SR85DET
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Re: Misfire when revving, but not at idle

Postby SR85DET » Sat Mar 07, 2015 7:26 pm

Did you verify that the ignition is advancing when you rev up the engine?

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ToeKnee805
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Re: Misfire when revving, but not at idle

Postby ToeKnee805 » Sat Mar 07, 2015 8:11 pm

Ok guys an update:


Ignition is advancing like it should
CLeaned MAF - No Change
Tested MAF per FSM, MAF is Good
Pinched off Fuel Return - No Change
Found vacuum leak @ Cold Start Injector - Fixed Lead - No Change
Deactivated TVIS (To Lean Car out) - Seems to rev a bit better, but still misses
Cat is Not Clogged
Compression Tested - 182 lbs. all across the board (A bit high for a Largeport??)

When i pulled the 3rd Cyl spark plug it was fouled out, like super black.

So im leaning toward a stuck open Injector?? Leaky Injector?? Bad wiring?? Am i heading to the right direction?


Videos of the misfire: WIth Cat on first and WIthout cat (More noticeable)

Image

Image
1986 Corolla GT-S -- Unmolested -- Now Resto Project
1985 Corolla GT-S -- Turbo Levin Track Car
1982 Corolla 1.8 -- Sitting collecting dust

totta crolla
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Re: Misfire when revving, but not at idle

Postby totta crolla » Sun Mar 08, 2015 4:08 am

A diagnostic test should rule out the TPS and it may point you in the right direction.

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ToeKnee805
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Re: Misfire when revving, but not at idle

Postby ToeKnee805 » Sun Mar 08, 2015 3:27 pm

I pulled the injectors and #3 was cracked in half. I replaced the injector and the misfire is now gone. My problem now is that the engine won't rev. It will idle fine but it it just doesn't want to rev when I blip the throttle. It will choke out. If I put a can of brake cleaner on it it will rev amazing. Could it be that my other 3 injectors are clogged? Starving me of fuel? I've tried checking for vacuum leaks and I'm good. And also pinching off fuel return with no change. My fuel pump is good because the car ran fine with the old setup.
1986 Corolla GT-S -- Unmolested -- Now Resto Project
1985 Corolla GT-S -- Turbo Levin Track Car
1982 Corolla 1.8 -- Sitting collecting dust

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ToeKnee805
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Re: Misfire when revving, but not at idle

Postby ToeKnee805 » Sun Mar 08, 2015 7:00 pm

FIXED!!

The fuel rail feed regulator was stuck closed, starving me of fuel. This is what happens when engines are stored outdoors I guess
1986 Corolla GT-S -- Unmolested -- Now Resto Project
1985 Corolla GT-S -- Turbo Levin Track Car
1982 Corolla 1.8 -- Sitting collecting dust

AE86_INL
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Re: Misfire when revving, but not at idle

Postby AE86_INL » Mon Mar 09, 2015 1:12 am

I had that same issue. My igniter was the problem since i was running red top injectors on a blue top engine. Did you check that?

allencr
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Re: Misfire when revving, but not at idle

Postby allencr » Mon Mar 09, 2015 7:57 pm

ToeKnee805 wrote:...fuel rail feed regulator was stuck closed, starving me of fuel.


What is that?
The fuel line from the filter banjo bolts to the rail with or near a little round accumulator/pulse damper thingy that is threaded into the rail IIRC. It should not control fuel.
The fuel regulator has 2 bolts and 2 hoses going to it, 1 for vacuum & the low pressure return to the tank that you've pinched.
//
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OK. Thanks.
I didn't think that a damper thingy would be designed to kill flow if it fails.
Last edited by allencr on Tue Mar 10, 2015 12:22 am, edited 1 time in total.

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ToeKnee805
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Re: Misfire when revving, but not at idle

Postby ToeKnee805 » Mon Mar 09, 2015 10:17 pm

Yeah the pulse damper wasnt bouncing up and down with my revs that was causing me to starve.(Big ass banjo crew)
1986 Corolla GT-S -- Unmolested -- Now Resto Project
1985 Corolla GT-S -- Turbo Levin Track Car
1982 Corolla 1.8 -- Sitting collecting dust

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