Motor won't rev over 5200-5300rpm... WTF???

[yullose]

I'm about out of ideas now.

I've been screwing with this car for 2 weeks now and still have the same problem.

5200-5300 the motor falls on its face and sputters... like a soft-touch rev control hits it.

I've gone over EVERYTHING.

Cam sensor re-adjusted/confirmed dead-on.

Crank sensor replaced - gapped at .025".

Brand new AC Delco coilpack and module.

MSD wires are good.

Autolite AR3935 spark plugs.

Tried multiple chips.

Brand new A1000 fuel pump.

Brand new Magnafuel regulator.

All grounds and ground wires have been checked and doublechecked.

Compression checked - all 6 between 145-155lbs.

I'm running Sunoco 112 leaded race fuel + straight meth

I've tried both alky and race chips, with and without meth injection.

I've had cronic KR problems too... and I wonder if it's related to the valvetrain. I was getting 15 degrees KR just free-revving in the driveway... I went over all the valves and tightened them another 1/4 turn. That helped a little, but not completely.
When I adjusted the valves, I set to zero lash, then another 1/2 turn. After the re-adjustment, they are now at 3/4 turn in from zero.


I'm starting to wonder if this is a mechanical problem now.

Before replacing the entire top-end of my motor, it would rev clean up to 6200 no problem. That was with ported irons, beehive springs, stock rockers and 214/.548 hydraulic roller.

The changes I made were:

TA SI aluminum heads, complete with their springs.
Springs are: 140lbs on the seat and 325lbs @ .584 lift
1.65 T&D roller rockers... (increasing lift from .548 to .584)
Champion aftermarket intake & plenum

I'm not running an RJC plate... (yet)

So that leads me to two possible conclusions...

A) The 1.65 rockers are too much for my cam/lifter combo and are collapsing the lifters at high RPM.

B) The Champion intake & plenum have airflow distribution issues and need the RJC plate between them.


A few things I HAVEN'T tried yet:

1) Replacing the ECM (I only own this one with modded drivers for the 83's)
2) Replacing/inspecting the injectors (they worked fine in the old combo)
3) Tightening the valve lash even more...


Any other suggestions ??? I just don't know WTF to do... and I'm running out of ideas.

Here are two PL files from this morning...

The 2nd one is with the knock sensor unplugged, just for comparison. It made NO difference whatsoever.

 

[Dabigguy]

Did you install/test the valve springs yourself? They may not have the proper install height, causing low spring pressure and valve float. Maybe a broken spring?

 

[86WH1turbo]

I agree about it possibly being the valve springs. Is 325 what the cam calls for? I have a 218/218 roller and if I am not mistaken the open pressures were in the 420 range. Of course I had to go to +.050 keepers to get that. I dont know a ton about cams and springs but its a place to start.

I also had that problem years ago with a BBC. Would die at about 5800 and the cam was good to 7000. It turned out that the springs were to weak. I went with a more reputable spring at the time.

 

[TurboBuRick]

Hmm, thinking maybe to loosen valve lash. Maybe some valves are hanging open a little at higher rpm's. I would try re-adjusting.

 

[DailyDrifter]

I'm going to say valve springs also.

 

[yullose]

Hmm, thinking maybe to loosen valve lash. Maybe some valves are hanging open a little at higher rpm's. I would try re-adjusting.

Funny you mention this...

I just spent 10 minutes on the phone with Jason at RJC...

What a super cool guy... very helpful and patient.

I ordered a powerplate from him... but in the conversation he offered several great ideas... one of which was... loosen up the rockers to zero lash.

He said depending which lifters I'm running, some of the Comps (885's) need to be @ zero lash. He said if you preload them, they will pump up at high RPM and cause all kinds of problems.

THAT makes alot of sense to me... I think I'll try going that direction next.

 

[yullose]

The heads were built at TA Performance, to my specs... I gave them all the cam info... and they matched it to my combo. Everything is brand new...

I think I'm going to go with the looser valve adjustment idea for now... The lifters were put in by the car owners previous engine builder, so I'm not sure which they are. If they are pumping up at high RPM's, that would explain the problem.

The RJC powerplate will be here tomorrow... so that will eliminate one more possible problem once I install that....

 

[TurboBuRick]

Keep us posted.......

 

[yullose]

Keep us posted.......

Oh, I will... lol

I tried throwing money at the problem... and it did nothing.

Now I will try some common sense and see what happens.

It will be a few hours before I can update... Fedex just dropped off the rest of my nitrous parts... so I 'gotta get that stuff on too. lol

 

[ttypewe4jim]

If you cant get it figured out by the weekend... I will be up that way, and could swing by and give you a hand shoot me a pm if you want some help.

 

[pressured]

rev trouble

had same problem. sputtering at 5400, almost sounded like hitting a rev limiter. turned out to be 3 month old beehive valve springs. car now has k motions and revs and pulls hard to 6k+

 

[1of1547]

Hmm, thinking maybe to loosen valve lash. Maybe some valves are hanging open a little at higher rpm's. I would try re-adjusting.

I had the valves in my old Redneck truck to tight and had the same problem. It was very sluggish and would not rev past 5000 or so. I took it to the local motor head and he helped me adjust them properly. It was literally night and day difference. It revved twice as fast way past 6000.

 

[9SECVSIX]

Lifter Preload..

I have been messing around with the 885 lifters on a 224-224 cam in my motor, I have found the valve train to be very noisey with 0 lash (warm motor) but it's the only way the motor will run strong and not knock. Even with 1/4 to 1/2 turn with 180 psi seat presures the motor just rattled from knock at light throttle...I put them back to 0 lash warm and the motor once again stopped knocking and pulls very strong. Am using GN1R heads and 1:65 rockers. I think when you set the valves at 0 lash your going to see a big change in performance...of course the valve clatter going to be there. For those think my cam is to big it's in a 278" motor Good Luck.

 

[yullose]

Well... I just finished going over all the valves. I set them at a tight zero. Turned them to zero lash, then snugged down the locknut while holding the adjuster with the allen wrench, letting it budge just a cvnt hair clockwise (tight).
It's about as close to zero as I'm 'gonna get. The motor was still warm when I set them.

I fired it up a few minutes ago and it's still fairly quiet. Didn't get to test drive it yet 'cuz I still have other stuff going on the car (nitrous system) and need to let it sit overnight.

FWIW... all my valves were exactly 3/4 turn in from zero. I checked every one of them when I went over them... just to confirm where they were before.

I did one cylinder at a time, bumping the motor to TDC with a remote button. It was a piece of cake.



I'll take it for a ride tomorrow after the RJC plate goes on... and if it's all good to go, I will load it in the trailer and try to get a pass or two at Maple Grove.

 

[Reggie West]

Did you call TA and see what they have to say about it?

 

[John Wilde]

I am not saying that your car has this problem but I had those symptoms with a bad cam.
If the problem continues disconnect the power to the ecu and have a friend crank the motor over while you watch the rockers go up and down.
In my case one lobe was more than half gone...

 

[bison]

Could be a module problem too. Does the tach needle go backward really fast as it sputters?

 

[yullose]

Could be a module problem too. Does the tach needle go backward really fast as it sputters?

Nope... and I just replaced the coilpack and module with brand new AC Delco units...(new crank sensor too)

I'm really starting to think its the lifters pumping up at high RPM... causing the valves to hang open... It really does feel like a rev limiter or valve float.

I'll know for sure tomorrow when I test drive it again...

I'll probably run it w/o the RJC plate first... and again after installing it... just for comparison.

And no Reggie, I didn't call TA... I did some research and confirmed via my head build sheet that the springs on these heads are perfect.
140lbs on the seat and 325 open...

The only thing I *don't* know about my motor, is which lifters are in it...

Jason at RJC told me the 885's will pump up and do exactly what I'm experiencing... so that's the direction I'm going at the moment.

All the valves are zero-lashed right now... and the motor still runs/idles quiet... so at least I don't have the excessive valvetrain noise I was expecting.

 

[yullose]

I am not saying that your car has this problem but I had those symptoms with a bad cam.
If the problem continues disconnect the power to the ecu and have a friend crank the motor over while you watch the rockers go up and down.
In my case one lobe was more than half gone...

The cam is a hyd roller and is cherry... I just had it out of the motor for inspection and it still looks like new.

 

[Reggie West]

I would not add any more parts to the mix until you isolate whats causing the problem.

Did you get a reprogrammed chip and injectors checked out OK?