LT5 technical problem

[8upZR1]

Hello all, you may remember my previous posts, I had a no start problem a few months ago. Much has happened since, but still no action. well sort of. I have not touched the car for about 2 months now. Last night I pulled the passenger valve cover to see if I could find any problems. None to be seen. I then put the plug wires on the plugs and cranked the motor without the valvecover on. It fired, and ran, and spewed a geiser of oil. But it did run. I put the valve cover back on and.....no luck. Still the same problem. Anybody have a clue? Should I just run the motor sans valve covers? Maybe Ill make the switch to mineral based oil first.

My wife suggests swapping valve covers (typical woman) but I think Id rather not. My theory is as follows.....Oil pressure is pumping the lifters up and causing valvetrain to stick open. Is this possible? Are there any oil restrictors in the heads? If anybody knows, Ill be nice to you.......

[Peaven]

You ran the LT5 without the cam cover on? :jawdrop: I'm no expert, but you don't want to do that again, as the cam covers more or less act as bearings to keep your camshafts from flying off of the heads.

The cam covers are l/r, and matched to the heads anyway, so swapping them isn't an option. Jeff, Johnny, or one of the other more knowledgable guys can chime in here.....:eek:

[Jeffvette]

I'm no expert, but you don't want to do that again, as the cam covers more or less act as bearings to keep your camshafts from flying off of the heads.

The cams are held in place with reatiners. Not just the cam covers.


Interesting tactic. Messy, but I like it.

I assume all the spark plugs were put back in on that bank when you started it? If it was a oil pressure issue, you would think the motor would run until excess pressure caused the lifters to stop functioning.

Also which side of the motor was this on. I'll run it through the master wheel and see what I can come up with.

[Peaven]

The cams are held in place with reatiners. Not just the cam covers.

There's a reason noobs are noobs, but at least we can learn:o ....I stand corrected, thanks Jeff.

And after reviewing 8up's posts, i was obviously duped by the swapping valve covers comment....nice one, 8.:)

[jonszr1]

wow, a deal like this could make one eat nails!!!! just tossing stuff out there . Could the valve cover some how be hanging a valve or valves open. I don't know the clearence. Does the motor spin over easier with the cover off? did you look on the underside of the cover maybe somethings hitting or moved.when ya put it back on? just thought to throw some stuff out there????????:icon_scra

[leonardpower]

There are no restrictors in the oil ways to the valve gear. Running the engine with the cam covers off (not recommend) with just the retaining caps in place will allow the camshaft to lift away from the head slightly as the retaining caps are a bigger bore the the camshaft line bore. This may let the valves down on to the seats if the tappets have become jacked up i.e. solid.

[8upZR1]

The cover I pulled was the passenger side cause it only takes 8 minutes to remove with everything in the car. I expected to see that the clearance between the lifters and cams was non existant even when you push down on them. But I had plenty, so I figured that wasn't the issue. I ran a compression test on cylinder 6 and it was good, 140 or something. This shocked me. I was just thinking that there is no reason why this motor should not run. So I put the plugs back in and wires on without the valvecover and tried it. SURPRISE!!! Even my wife came into the garage. I even started it a second time just to make sure I wasn't hearing stuff. The motor sounded perfectly healthy, just slightly different with no valve cover.

You can imagine how incredibly angry I was when I put the cover back on and its back to step 1. I have thought about my own theory, and have concluded that most likely oil pressure is not the problem as I remember thinking this a few months ago and trying to start the car without the oil filter attached to see if it would fire without any pressure on the lifters. It did not. And besides, behavior like this is childish and borderline stupid.

So now I sit here and wiat for intelligent thought...............Still waiting............

[tccrab]

Just a thought...
Probably way off base, but...
It's mechanical or it's pressure.
Mechanical could be that somehow the cam cover when tightened onto the head causes the cams to push harder on the valves and not allow them to seat. On just one side.
That just does not make sense though, as there are cam retainers under the cam covers, so...
Lifters, is there any way that yours are damaged? On the wrong cams? The intake is different than the exhaust.

Pressure. Hmmm...
Somehow you're getting so much blow-by from lower in the engine that it's pressurizing the area under the cam covers and that air pressure is holding the valves open? That's just plain crazy. I must be a nut.
Maybe something to do with too much oil pressure?

Gosh, I'm just pulling ideas out of my butt, I can think of dozens of reasons why none of the ideas is even close.

I remember that you've had the heads off a few times, what condition are the head gaskets? Is it possible to put them on the wrong side?
Did you do anything with the lower end at all? Rings bad, maybe?

Here's my thinking,
Cam cover off, engine starts.
Cam cover on, engine won't start.
Problem is something to do with the heads being sealed.
Either oil pressure or air pressure is keeping valves from sealing in head.
Have you tried starting the engine with the oil filler cap off?
!!!
That would tell you if it was air pressure or oil pressure holding the valves open.
Wait a minute, have you measured the tolerences in the Cam Covers where they act as cam bearings? What if you've got a bent cam or one of the holes is slightly out of round, allowing the cam more movement that it should have? It wouldn't need much to keep a few valves open.

My brane (mis-spelling intentional) hurts. Must be overworked.

Just tossing out some stupid ideas...

Good luck!

TomC
'90ZR1 #792

[8upZR1]

I have tried starting it without the oil filler cap and it makes no difference. The engine turns over nice and all sounds are normal, even when it ran it sounded good. After it did not start with the valve cover put back on I checked the compression on #6 and it was 0. I have never heard of a problem that causes varying compression but it obviously exists. The lifters are the originals. After the head gasket blew I removed them and put them in a plastic bag full of oil. Never touched them. The 3rd time I took the engine apart I noticed they were locked in the fully extended position. Through the use of extreme force I managed to unlock them. Afterwards they seemed to be in good shape. They rotate and slide in the bores beautifully.

When I have a minute I will remove the cam cover again and re-measure the clearance between the lifter and the cam. If all else fails I will instal a new set of lifters.

[petefias]

Did you check the compression in 2, 4, and 8? Are they good? If 6 has good compression without the covers the answer is in the valvetrain.

My guess is that the camshaft is broken, I know it doesn't make much sense. Maybe with the valve cover installed there is too much drag on the cam and won't turn, with the cover off it just turns enough to run.

Another possibility is what was suggested before: the lifters/pushers are "overextended". With the cover off the cam lifts off enough to not matter.

Good luck and let us know...

[jonszr1]

Here is a young man that might be able to help you out. He is without a doubt one of the most knowledgeable Lt-5 guys around. plus he is one of the most kind and helpfull people I've ever met. Run your problem by him. tell him I sent you . Opps I'm brad his name Corey Henderson ph# 210 867-6286. He owns hpt in New braunfells tex . I just know he can figure this out . Good luck.

[8upZR1]

Thankyou for the phone #. I will give him a call today. Initially I only checked compression in #6 cause that was the cylinder that happened to be on the power stroke and therefore both cams were riding on the base circle. I had a theory that the valves were open on the base circle but that was just not the case. I only checked the compression of the other cylinders after the motor failed to start with the valvecover removed. The cams are good, and correctly installed (L,R,I,E). The cams are held perfectly in place by the small caps that go on before the valvecover. There is no play. If the caps were pressing down on the cams they probably would not turn easily, but mine do. I thought the lifters were over extended, however, they are completely empty of all oil and can be compressed slightly by hand. When I had the valvecover off I pushed against the lifter and this created a measurable gap between the cam and lifter. This tells me that the valves are completely seated, as the valvespring would be pushing against the lifter and the gap would be closed if the valve was not on the seat. I checked the valve job seal by pouring water into the intake and exhaust ports to CC them. The ports hold water without any leakage. Also I believe that this is mostly intake related as I was seeing combustion occur inside the injector housing ports when I tried to start the motor without the plenum, and minimal flow coming from the exhaust.

I just don't know anymore. I will call this Corey fellow, perhaps he has experienced this. I hate the LT5, and everyone who owns a working example. F you all.

[8upZR1]

just kidding ya'll are true gentlemen

[jonszr1]

Left corey amessage about your problem. Told him this could be the ultimate brain teaser. I just got afeeling he can solve this. If not I suggest a car exosisum. I know of a couple of preachers!!!! just kiddin . Good luck my heart goes out to you

[8upZR1]

Thankyou, I haven't had a chance to call yet, so Ill probably call him Monday. If I get a chance between house work today I will remove the valvecover again and check out the cylinder that showed good compression and then lost it. I am assuming that without compression any slack in the valvetrain will be taken up and the valves will be open. Who knows?

[jonszr1]

Coreys going to be at the sema show in vegas till fri I believe. I'll pm you my E-mail. WHy don't you write up everything you have done and I'll foward it to him and see If he can come up with an answer.

[8upZR1]

Its been a while, but I have excellent news, my LT5 fired and runs. In the end it was the lifters. I installed a new set and they seem to do the trick. I have never heard of compression varying like mine did but it is absolutely possible.

Now it seems that I have an even bigger problem. The motor will fire but it takes forever to crank and ussually you have to floor the throttle for it to fire. The mixture is crazy rich so I am guessing that the ecu goes into flood clearing mode when the throttle is floored. When it runs it will nit idle by itself, you have to give it gas. Performance is awful. It feels like a small displacement big turbo car in 5 th gear at 20 mph. It literally cannot keep up with traffic. But once the motor passes about 4K RPM it starts to run normal. But getting to 4K is a serious struggle. Full race engines have snappier low end torque. I refuse to believe I lost this much low end torque from porting the intake. Its just impossible. So what could it be? Fuel pressure looks great, the O2 sensors are new and they look like they are behaving normally, except that they show rich for the first 4K rpm. My secondary throttles are removed, but they always have been. No SES light or codes to be found. I was thinking maybe Idle air control but then why would everything be OK up top. I have tried 2 computers, one with haibeck chip, and the other with a GM piece. No difference. Engine key doesn't make a difference either. Why so much fuel? I just dunno. This Lt5 has been a mission to say the least.

But at least I can cruise aroubd town in my vette. I thank everybody who gave me input and helped my figure out this machine.

[jonszr1]

Patrick, give Corey a call!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 2108676286

[tccrab]

Congrats on getting it running again!
What a long and painful road you've been on.
If the hose to the MAP sensor isn't sealing it will cause the engine to run rich. The MAP sensor input is the number one contributor to pulse width.
Check the hose, then check the sensor.

Good luck!

TomC
'90ZR1 #792