Tough one..

[Razor]

Help a fellow Buick brother out. I dont know what else to do to help him. maybe someone reading this can make heads or tails.

Car has a 221 cam. The problem is once the RPM's hit 5K, the car stops pulling until the rpms go past 5400-5500 then the car screams to 6k. It has this big flat spot at around 5K that clears up then pulls strong.

this is what has been done. See if anything has been missed.

MAF swapped out for known good GM,
Coilpack+ignition module replaced with known good one.
New plug wires MSD's
new plugs double changed in case of bad set
ECM swapped for known good one.
6 different chips.
Heads and cam were swapped thinking problem was valve springs
All numbers at idle and while driving are withing normal limits. vacuum is low due to cam.
Grounds to motor solid
Fuel pressure stable per boost being run.

It feels electrical.. like if it was running out of juice.


Can a bad cam do this condition? Bad turbo? what else besides springs.. and if springs were to be bad, why does it clear up after 5400-55 rpms.

Does it in 1st, 2nd, 3rd gear

whew..

Any help opinion welcome.

 

[turbot2496]

What kind of boost control is he using? Does it stop building boost or loose pressure when he has the power drop off? I guess I would start checking around the turbo and the boost control if I'd checked everything you've checked already.

 

[Razor]

Stock WG solenoid. Boost is stable and we're running only 14 PSI to isolate the problem. Feels like an anchor was thrown out of the car.

Will also do it in neutral, but not as much, if we rev the motor. So its RPM based not boost related. Tho its scary to hear our motors rev'd in neutral above 5k.

Keep the ideas coming

 

[turbo nasty]

Double check system/alt voltage output for stablility throughout the range.

Gnds are important but so are the +POS connections.
Check for wire secure mount at the back of the alt and all the fusible links/wires at the pos connection on the starter stud.

Roller valvetrain ??? If so, are lifters correct ??

When did the problem arise ?

One thing I can see, if you get the car figured out at 14 PSI with a certain heat range of a sparkplug. Then if you run high boost the motor may like a colder plug...something to think about ?

Sure you don't have some crap gas and have a fresh fuel filter?

Even though it is hard to find a place(other than a track) with enough room to wind the car out to 6k in a couple of gears, it is still best to drive it to test so the engine is underload so the ECM is working to like it was meant....spark, fuel, KR, O2, all the data streams are inputting with the engine loaded.

As far as revving the motor that high without load, that freespinning/unloaded inertia on the recip assem. is not good best to have some load on it.

 

[Razor]

The voltage reading on the direct scan recordings have been stable, that doesnt discount any RFI noise that the alternatior may be producing. One neat test may be unplugging the alternator and running the motor on battery.

Its a HYD flat tappet cam. Non roller.. good thought..

Problem has been there for quite some time, probably a year, tho you know some Buicks sit dormant with issues for a while. Just that its starting to get critical with this one.

many changes in gas, and the gas is fresh. Fuel pressure is stable, hence why I didnt think filter. If fueling was dropping off, or O2's were crashing, then I would suspect fuel, but thats not the case. Good thought/input.

Plugs are stock heat range 43's. No reason to run colder plugs or high boost till the car runs correctly on low boost. I agree with rev'ing in neutral.

I think you know why I said "Tough one"

See ya this weekend at BMP.. hope you can make it.

 

[turbo nasty]

It is quite a bit of load for the battery to handle without the alt. Different if it was points only, these EFI suckers have all the sensors, ecm, tach, fuel pump, gauges, ign, etc.

You are going to get voltage drop, and even if it did not fall out of range to still run decent, that volt drop will cut the fuel pump output and the ign will not be as hot so that will not help narrowing it down.

I would steer clear of that test.

Double check all the connections at the ECM plugs ...all the pins.

Naw, will not be able to make it to the meet...Have to work this whole weekend. Love to though.

I know,... it is the high speed muffler bearing yuk yuk yuk

Does sound like a bad connection/electrical. Maybe the crank and cam sensor for adjustment.... a good visual of every sensor and wire on the whole flipping car. Make sure the wires are plugged in good, no pinched wires, old repairs that have crapped out, etc.

 

[TS6]

Bad spot in the TPS?

 

[ijames]

Cam sensor setting or maybe the sensor itself? Unplug it after cranking and see how it pulls.

 

[RobR]

Were the springs the same part numbers on both heads? If so, change to different springs. Could be a harmonic problem where they float until it passes that condition.

Just a guess...

 

[Razor]

Ok.. I will add silicone lube to the muffler bearings and top of the blinker fluid reservoir.

As far as I can tell, the wiring is original and "unmolested" I will get a couple wires added for additional grounding just in case, and have him change the fusible links... in case the coilpack is losing power through them.. A well charged battery ought to run the car in first gear at low boost just for revs.. so i'll still play with this one. Worst thing that can happen is no change.

TPS doesnt drop out on the DS recordings. So that ones ruled out.

Carl.. great idea.. unplug the cam sensor..

Rob, the springs were brand new from Champion. But hey anything is possible.

I'll add these to the suggestion list

 

[Reginald West]

I had this problem with my stage 2 car hafe way down the track the car would fall on its face and then begin running like hell the rest of the way. I chased this problem for almost a year and one day a friend walked up to the car and said your starter shield is loose. Sure enough the shield was loose and falling down and shorting out the starter. It only happen when the car was accelerating hard. Get another set of eyes to look at it sometimes we don't see whats under our nose.

REG

 

[87tr4u]

my 2 cents

get your hands on a ocliscope (sorry for spelling) and see if your spark is falling off at 5k and picking up at 5500

the scope will also let you see maf range and patterns and will work on almost all sensors and show, range, patterens,graph,spikes and drops,etc


if you have scanner see if it has wiggle test,most snap on 2500 scanners have this function


good luck

 

[HellOnWheels]

Sounds like the fuel pump "sock" filter collasping momentairly?

Good luck,
HellOnWheels

 

[QuickWrench]

First...I'd love to see the Direct Scan file(s) on this. Zip 'em and email to Quickwrench@Runbox.com. Happy to take a look.

Let's address this stuff:

-> What do the injector DC/PW's look like before/during/after the flat spot(s)?

-> Has this happened since day one with this camshaft? Is this camshaft using non-stock pushrod lengths? What kind of lifters are they? If this engine's gone through several changes, what were they?

-> Again with the DS file: is the car going into AE/DE mode at WOT, or anything else goofy?


Thanks.