Jc803

iTrader: (2)

I changed my spark plugs before I went to the track. I go to the track and notice a loss of power/slight vibration/rich air fuel ratios after 4k rpm and I'm running .8 tenths slower than normal in the 1/4. So I figure it must be the plugs since thats the only thing I changed. I change the plugs and that didnt work so I kept checking things.

Plugs - replaced
Plug wires - replaced
Coil Packs - Bought a new one and swaped it one for one, test drove, did that all 8 times
Fuel pump - checked and fuel pressure is fine
Fuel filter - replaced

Its not the tune, just tuned it days before the plugs
I also dont have a single check engine light.
Also tonight I data logged and I'm not getting any knock at all.

trw427ssrs

Have you checked the crank thrust? (end play) If you have to much thrust the reluctor will misalign with the crank sensor. We have see that on a few engines when the crank thrust wears.

poltergeist 02

iTrader: (65)

What valve springs do you have and how many miles are on them?

Jc803

iTrader: (2)

I haven't checked the crank thrust end play or valve springs. I have PRC 650 double springs. I'm going to try to check those today.

So it could be springs or thrust bearing, is a bad fuel injector a possibility and something i should add to the list of things to check

redbird555

iTrader: (14)

i'd also check the crank sensor and swap it for a known good one. I had a high rpm misfire over 4500rpm. would only do it under load, no CEL and the car drove perfect. ended up the crank sensor was bad

ez2cdave

Or you have more than one bad coil pack and swapping one didn't completely identify the problem . . .

Jc803

iTrader: (2)

Ok so i just checked the springs and none of the inner or outer are broken. As for milage and age they are 3 to 4 years old but have about 8k miles on them. As i said they are PRC 650s. Anyone think i should replace them anyway?

For the coil packs, you're right. It could be multiple bad ones. Not likely since it was running fine one day then bad then next, but possible. I'm going to buy a timing light and test each one that way.

Thanks for the info on the crank sensor. I'll replace that just because. Won't hurt to and they're cheap enough.

Now no one has mentioned lifters. Could that be a possibility? I have ls7 lifters also with about 8k miles on them. That would obviously be the last thing i want to change but i will if i have to.

I suppose push rods are a possibility too but doubtful. They are aftermarket hardened ones, not sure what brand. But if i replace the valve springs I'll check those while I'm there

poltergeist 02

iTrader: (65)

I would have the spring pressures checked. After that I would check the compression.

poltergeist 02

iTrader: (65)

How old is your battery? Also, you could check the alternators output.

Jc803

iTrader: (2)

If i take the springs out they're getting replaced. I'm that lazy lol. Checking compression isn't a bad idea. Battery is 6 months old and doesn't get any hot temps to wear it down because it's in the trunk. Voltage is over 14 volts so shouldn't be a problem there.

But first thing tomorrow I'm going to take a look at the crank sensor. Engine has 8k miles on it and first two oil changes had metal shavings on the pan bolt from break in. I'm thinking because the crank sensor is magnetic maybe it got some shavings on it throwing it off only at high rpms

Jc803

iTrader: (2)

I think i might be on to something. Although I'm not getting any crank position or can position codes i decided to pull them out and replace them.

But when i reached my hand to the back of the intake i felt a sensor just kind of flopping around but still in its hole. I pulled it out and look what i found. The MAP sensor was placed in with black RTV and had worked is way loose.

Normally i wouldn't think this would effect anything but i don't have a MAF sensor. I tune purely in speed density off the MAP. And with it partially in place that would explain why cruise is fine but wot is sucking because it's not getting a good reading /vacuum leak.

Going to clean everything up and put it back in. Cross your fingers

Jc803

iTrader: (2)

Well that didn't work. Not any better. Guess I'm going to buy a cam and crank sensor and new PRC springs. I just hope i don't have to tear down into this motor

trw427ssrs

Did you check the crankshaft end play to see it the crank is moving back and forth?

Jc803

iTrader: (2)

No. But I'll check it now

I did just replace the crank sensor and no change. Still doing it

Jc803

iTrader: (2)

Actually i don't have a dial indicator right now so I'll just have to eye ball it for now

Edit: i do have a feeler gauge. Took it with me. But didn't even use it because the crank is barely moving at all. I'd say somewhere between 0.005 and 0.010. Looks good to me.

Plus i was reading where guys were getting crank codes from too much run out. Between the run out that I'm getting and a new crank sensor and never getting one code about the crank sensor i think it's time for me to move on to something else

trw427ssrs

Ok just something to check I've seen that problem with on codes.

Jc803

iTrader: (2)

No you're right. It's good to check everything and i appreciate you reminding me about the end play. I'm starting to get flustered.

I'm not even going to worry about changing the cam sensor. I think it would be pointless. I think this has to be a mechanical problem and not an electrical. Next up is to replace the valve springs and check push rods while I'm there. I just hope its not lifters or a head gasket or something.

Jc803

iTrader: (2)

One more thing. When it starts missing at 4k rpm and up, it goes very rich. Normally it's around 12.5-12.7, but now its anywhere from 11.2-12.0. So something is effecting combustion. My guess right now is maybe weak springs, valve not opening all the way, not getting enough air throwing the af ratios off.

But what do i know. I've been wrong about the last ten things I've checked.

Just ordered new PRC 650 springs. I read a couple threads where some guys were only getting 6k miles out of them. Hopefully this does the trick

dr_whigham

iTrader: (49)

Cracked plugs? I know you said you replaced them but it DOES happen. I'd pull them all and check them... Again.

HioSSilver

iTrader: (8)

Do you have a udp? I have seen them go bad and cause a high rpm miss fire.