Major malfunction & I can't find it.

[TurboJim]

Could you be sucking the air filter shut?

 

[Fasstcars]

I had a car once that was doing the same thing and it ended up the tach was shorting out. It would wonder just a little on the face of the gauge like it had a plug miss, but it ended up being the gauge.

 

[BoostKillsStres]

Check the orange wire to the ecm make sure its not about to break or have a bad spot in it at the BAT. Is the + BAT cable burnt anywhere or getting up against something at that point? Check ti all the way to the starter to be sure. Sounds kinda like your either loosing power to the ecm or ign so could be power or grounds, check them all.

 

[wiked87gn]

worst case is a cam gone bad, at idle it will work and rev just fine but under load it will be quite obvious specially on be big top end, could be a bad cam just thinking here.. hope it turns out something that is not that complicated, I also had a similar problem like that turned out to be the Coil pack, put in a new one gapped the plugs at 28 and problem solved..

 

[turbolou]

Reply

With that many miles on the engine. I would suspect weak or broken valve springs or some thing else in the valve train. Could there also be any rev limiting device that could be causing it?

 

[wiked87gn]

Re: Reply

Lou if you read his post he has new beehive springs, and new cam, so it could be that his cam went south.. i would also agree with you about the limiting device if you have any install in the car check settings on it.

Originally posted by turbolou
With that many miles on the engine. I would suspect weak or broken valve springs or some thing else in the valve train. Could there also be any rev limiting device that could be causing it?

 

[turbolou]

Re: Reply

Originally posted by turbolou
With that many miles on the engine. I would suspect weak or broken valve springs or some thing else in the valve train. Could there also be any rev limiting device that could be causing it?

I missed the new cam & spring part! Is the spring tension correct for cam application? Thats critical with roller cams.
Checking seat press. isin't enough. Over the nose press is also important.

 

[azgn]

may want to check the valve lash?

 

[jswmotor]

I agree with Doug Jacobson.

Check the plug gap. My old GN did this. The gap was just a little too much and did this "sputtering up" at the upper RMP range under full throttle and my plugs were new. Perfect running car everywhere else. I thought it was everything else also. I found it last!!!!

Good luck.

 

[buzzman]

it has already been said but, I would pop the valve covers and make sure that i had complete movement of all valves, sounds like one i had with two bad lobes

 

[wiked87gn]

i am going with whipped cam lobes, the spring may have been too much for the cam.. just my 02's.

 

[Ed Valvo]

Crank sensor hitting? Seen it before where crank flexes under power and hit the ring. Won't happen just revving it because there is no load....

 

[86gn]

Check the cam sensor for the tab missing or the metal disk under the cap could be loose..

 

[turboclam]

How old is the gas that's in the car?

 

[Slowhawk]

Could be valve float.Try turning down the boost and see if it still happens at the same spot.

 

[MeanBuicks]

UPDATE

OK folks. For sh!ts and grins I purchased a fresh set of CR43TS plugs. As BJM suggested, this time I bought eight and measured them all. They ohmed as follows: 7.6M, 4.6M, 4.6M, 4.9M, 4.5M, 6.7M, 5.0M, 3.8M.

I was surprised at the variance. I didn't use the 7.6M & 6.7M plugs. I gapped the rest at .030 and installed them with new Crane 8mm silicone FireWires. Results...

No change.

So, it's time to look elsewhere. Jim mentioned the air filter possibly sucking closed. Funny thing because that's really what the car acts like come to think of it. It just looses power & noses over really hard right at 4000. I have the standard setup consisting of a 9" K&N attached to a chrome Kirban MAF tube. Doesn't appear that anything is causing an actual blockage.

Looks like I'll delve further into examining the crank/cam/TPS sensors, wiring harness and valve train.

Thanks for all the suggestions folks! It is helpful.

 

[gnsrule]

Greg,
What kind of module you got in there ? I dont wanna beat a dead horse, but many will tell you a non GM module is crap. I've gotten 2 crap aftermarkets in a row. Beat my head against the wall for 2 months over that.

Good Luck

 

[gnsrule]

Under a load it runs real clean until 4000 rpm and just hits a wall. The engine just breaks up and stutters real quickly just like the stutter box on a bracket racing car. Won't do it at all below 4000 rpm or if there is no load. In park/neutral, it'll wing right up to 5000 rpm quicky & cleanly

Jim mentioned the air filter possibly sucking closed. Funny thing because that's really what the car acts like come to think of it. It just looses power & noses over really hard right at 4000.

Hmmmmm,
2 differant things here. The first leans me towards a module or spring problem, the second maybe your fuel filter is cloged or a pump problem or ??

Keep up posted

 

[MeanBuicks]

Actually, I'm not sure of the ignition module origin. It's a Red Regal T special which he says he tests before shipping. The one I took off in my quest for a fix was an Echlin from NAPA that's been working fine for a good while now (unlike the Wells junk from Auto Zone that preceeded it.)

I replaced the fuel filter last week with no change. Could be a pump problem I suppose as the current pump has over 100,000 miles. I have a hood mounted fuel pressure gauge but it's hard to go by that when the problem occurs since fuel pressure is tied to boost. When the motor noses over, RPMs drop, boost drops back and so does fuel pressure. Chicken or the egg first syndrome.

Craig, those two symptoms do seem contradictory but the problem seems a bit worse now and has more of an air/fuel starvation feel to it. Friggin' weird! This car has pulled some stunts in its day but this one about takes the cake.

Oh, and turboclam3, the gas in the car is about five to six weeks old.

 

[wiked87gn]

I bet my money on whiped cam lobes, maybe just a couple u better catch it before its too late..