part throttle KR

Right. So the car was having this problem to some degree before it went into storage for 6 months. During its down time, I had a bunch of things planned and was hoping the *one* of the things done would fix this. Specifically I was suspecting the cracks in the exhaust manifolds. But, now that its all together again, the problem is still there, and seems like it could be more pronounced. The storage made things worse. To make it worse, I did have alot apart and back together when it was off the road, so its mostly impossible to tell what if anything made it worse.

Anyway, I don't want to shotgun parts at it , and I don't want to be wasting time dinking around trying to fix it, since I have some jobs for other people I need to be doing. Since the car is 2 hours away at the prototype shop, I'm looking for suggestions of places to check and things to try when I end up back there.

The symptoms:
Under load, usually second or third, KR spikes to 7-8*.
This occurs usually below 3k RPM, and will happen when not under boost too.
WOT and down-shift will *always* make it 7-6-5-4-3-2-1-0 and steady 0 at all times under WOT.
This occurs with all pulley sizes, 2.4, 2.5, 2.85.
WOT pulls really hard, KR free.
WOT from a stop will fire some KR under load at first, but once it gets going it drops like a rock to 0*.
No codes thrown.
Fuel trims seem to be all over the map, but i'm not sure if its due to having the batt disconnected for so long, or in response to the KR.
LT fuel trims are around 110-115 "normal" driving (128 is zero point for the series one)
ST fuel trims shift radically from 110-148 whilst the problem is happening.
At WOT, injector p/w is 22.1, at part throttle when its knocking is at around 10.8.
Fuel pressure *seems* to be 45-50 PSI, though it goes up slightly when the engine is spinning faster. I say *seems* because the pressure gauge I had has a defective sending unit that weeps fuel from its enclosure, so until I RMA it, I have to suspect its readings.
When it boggs and KRs, you can hear an audible sound.
Never sets any misfire codes, only the KR.
Engine temp is great, steady 180, transmission is 185 (has a cooler).
Idle is smooth.
From looking at the scan tool, there is no part throttle knock when the EGR is doing its thing, but the hits a point where the EGR stops commanding any pintle position and the KR usually occurs shortly after.
I tried disconnecting the EGR, same KR.(just the code of course)
There is no extra KR at gear changes. Shifts are smooth, no slipping. Trans fluid level is good.


Some thoughts:
Brand new battery and ground strap.
Tired a different TPS - no change
Front bank of plugs look great, no visible sign of detonation, haven't pulled rear bank yet.
Wire set is in new condition.
MAF, TB, entire intake, LIM tract, as clean as clean can be. (Was recently dismantled and polished/etc)
EGR tube had a leak, previously, but was fixed.
Manifolds had all cracks fixed.
Power steering pump does have a quite a wobble, spins ok by hand, but could be on the way out.
If its fuel related, then why is everything perfect at WOT?
I do have a Walbro fuel pump thats been sitting around for ages I could try, since it won't cost me anything to put in.
Before storage, it has thrown a torque converter clutch failure code when in low gear going up a steep hill. This has happed maybe twice ever.



Anyway, any ideas I can try next time I am over there are welcome. It runs so sweet at full out, just under load this is balls.

Quote :

This occurs usually below 3k RPM, and will happen when not under boost too.

If this is confirmed, the knock must be false. Maybe something is rattling on the engine. Check that everything is tight. Maybe a bad motor mount?

AA wrote:

Quote :

This occurs usually below 3k RPM, and will happen when not under boost too.

If this is confirmed, the knock must be false. Maybe something is rattling on the engine. Check that everything is tight. Maybe a bad motor mount?

Thats why this is really confusing me, because I was under the impression that any knock that does not increase with RPM is false. In this case, high RPM is great. Just its the bog under load. I did fill the front engine mount with polyurethane, which might have accented some vibration in the engine compartment, so I'll have a peek around.

So far things to try later:
change fuel pump (since i already have another)
I could swap the FPR.
Check rear plugs for detonation evidence.
Check plug wire routing.
Coil packs? Can they have weaker spark at lower RPM?

I do not agree that any knock that does not increase with RPM is false. I typically see more knock after shifts, because the load is greater. After the engine has a change to increase RPM, the load is less and KR goes back down.

However, it's very unusual to see knock when not in boost. Since you verified this, it has to be false.

Even after serious (audible) knock, I have never seen any evidence on plug electrodes.

In our engines, the coil packs are supposed to have weaker spark at lower RPM, because this is typically less boost, so the A/F mix is easier to ignite with less energy. Even so, if your coil was bad, I don't see how it would cause knock. A missfire, yes.

Well, I'm not sure what to try next. I've done the following:

-Walbro fuel pump - It was lying around waiting to be installed
-Fuel pressure is sweet.
-Cat sounded like it was full of rocks, got it changed, exhaust sounds sweet, but still the KR
-Calibrated the TPS so the WOT point is exact, this very slightly allows the engine to get into Power Enrichment mode a little sooner in the throttle
-Checked the engine bay for knocking things (heat shields, bits and pieces), found a couple of odd things, secured them down, no change
-Un-plugged MAF, exact same symptoms with MAF unplugged.
-Modified plug wire routing- none are touching each other or the o2 sensor wire
-Took out the transmission hoses left over from the trans cooler- (they *could* have been rattleing against the engine), no change
-Check for bad FPR by unplugging vac line at idle and smelling the hose connections for fuel smell - all is good.
-Check vac line on Trans modulator for sucking up trans fluid into vac system - no problems
-Check out engine mounts, appear to all be in great shape, no engine rock when reving
-replace o2 sensor
-swapped out all 3 coil packs with 3 known good ones from the wife's 98 - no change
-brand new EGR valve (old one had been throwing a code for ages and I just kept clearing it) - made things a little more responsive part throttle and better MPG, but part throttle KR still there
-Checked harmonic balancer for cracked rubber etc, all good.
-Raised the BCA to uppermost position - This actually made the most impact, the "window" of throttle that would cause the part throttle KR got much smaller - The car became drivable at this point cause I can drive around the part that causes KR

At this point I'm wondering about a tune?, the KR shows its face at two points. If revved in neutral, it maybe kicks 1-2 deg when its blipped into boost. The main time is when driving in any gear, and giving it some gas, but not enough to make it down-shift. With just a very little throttle I enter boost. With the BCA lower, I enter more boost at the same throttle.

Am I hitting boost too soon for the computer to go into PE mode? I'm starting to wonder if my custom output plate and ported outlet shape on the supercharger is working too well?

When it KR's at part throttle its usually no more than 7 deg, and the timing goes to -4, which it really felt. But if you hammer it, it might start at 5 then drop like a rock, and the thing rockets.

If no one has any other ideas, I might find myself a datalog cable and see if sending a scan to Sinister Performance can shed some light on things. Maybe it just needs a custom tune, I have done alot on the stock PCM at this point...

I should mention, that the SC mods I made are incredible, with the silencer ports blocked there is NOTHING subtle about driving this. It hits boost very fast, and sounds like an exotic.

This is tough because of all the things you have done to the engine, but it reminds me of the "flash KR" created when doing the free Boost Bypass Mod. Like you say, the boost ramps up too quickly. So maybe doing the reverse in order to delay the boost might help?

just a thought but do you have any lifters that are ticking?

I don't own a scan tool to get all the reading but my 95 did the same thing when the boost control solenoid went bad. It actually started happening before it registered a code, and yes like AA said it acts kinda like the boost bypass mod. You said a code came up for the TCC right? Which code was it? What I found when researching my problem was that the bcs and tcc often show as the same code. if it was P1640 a new bcs might do the trick, but they can be tough to find.

Derek: the bcs is brand new within 2 years. So it *better* still be good...(though I do have another one from a different SC I could try) I can't remember the TCC code, as it was cleared and never came back a while ago.

Anyone know how to diagnose ticking lifters? I have no clue what to look for or listen for, there are no out of place sounds....

This weekend I am going to pull the VCs and check out the roller rocker alignment and torque, though its my understanding that if they are out things would have been destroyed pretty past, and the KR would increase with RPM.. but can't hurt to look.

I suppose I could rig it so I'm boost-less and see if KR still shows its face under mid throttle load...

Ticking lifters would be very noticeable. It would drive you nuts. They'd have to be banging together pretty hard to cause false knock.

As for "rigging" it, remove the little filter on the BCS and cap it with a vacuum cap. Viola! No more boost

Good call on how to rig no boost, I hadn't given it any thought yet on how to do it. Just to see, I'll do a compression check on all cylinders this weekend too, since Ive had the compression tester for ages without using it.

I can't remember if I mentioned it previously, but another symptom is that when under load and part throttle, the RPMs fluctuate up and down a little, with the exact same throttle position. You can noticeably feel the car bogging up and down and sometimes it will all of a sudden "rev freely" again. Like there was some resistance that comes and goes...


things are actually very similar to this:
http://www.gmforum.com/showthread.php?t=246743

Abaddon wrote:

As for "rigging" it, remove the little filter on the BCS and cap it with a vacuum cap. Viola! No more boost

Actually, I'd suggest unplugging the BCS electrical connector, or disconnecting and plugging the Actuator hose. As others here will attest, if you mess with that delicate and aging filter: Viola! No more filter...

Ugh, well still got this problem.
its not anything accessory related, and from using an auto stethoscope, its louder when the rear head is touched. But not when the LIM or VC is touched.

Gonna pull the VC to see about loose rocker, but.. Searching I found this thread:
http://www.w-body.com/showthread.php/46056-Stuck-lifter/page14

Looking at the previous pages, xtremerevolution is describing *exactly* what I am seeing. Also the info on how the knock sensor for the series one is different on the two is interesting too. His was a grenaded roller lifter. Doesn't make me feel good since I don't know when I can get to replacing the lifters, probably not till the snow flies and the car is stored.