LT5 technical problem - Page 2 - ZR-1 Net Registry Forums

jonszr1 · 10-25-2006

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 · 10-27-2006

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 · 10-27-2006

just kidding ya'll are true gentlemen

jonszr1 · 10-27-2006

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 · 10-29-2006

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 · 10-30-2006

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 · 11-15-2006

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 · 11-15-2006

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

tccrab · 11-15-2006

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

10-25-2006	#11
jonszr1 Join Date: Sep 2006 Location: lone pine and mammoth lakes Posts: 1,407	Re: LT5 technical problem 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.

10-27-2006	#12
8upZR1 Join Date: Jun 2006 Location: Thunderbolt, Ga. Posts: 253	Re: LT5 technical problem 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. __________________ IT IS THE FATE OF THE INNOCENT TO MEET WITH DEATH!!!

10-27-2006	#13
8upZR1 Join Date: Jun 2006 Location: Thunderbolt, Ga. Posts: 253	Re: LT5 technical problem just kidding ya'll are true gentlemen __________________ IT IS THE FATE OF THE INNOCENT TO MEET WITH DEATH!!!

10-27-2006	#14
jonszr1 Join Date: Sep 2006 Location: lone pine and mammoth lakes Posts: 1,407	Re: LT5 technical problem 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

10-29-2006	#15
8upZR1 Join Date: Jun 2006 Location: Thunderbolt, Ga. Posts: 253	Re: LT5 technical problem 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? __________________ IT IS THE FATE OF THE INNOCENT TO MEET WITH DEATH!!!

10-30-2006	#16
jonszr1 Join Date: Sep 2006 Location: lone pine and mammoth lakes Posts: 1,407	Re: LT5 technical problem 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.

11-15-2006	#17
8upZR1 Join Date: Jun 2006 Location: Thunderbolt, Ga. Posts: 253	Re: LT5 technical problem 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. __________________ IT IS THE FATE OF THE INNOCENT TO MEET WITH DEATH!!!

11-15-2006	#18
jonszr1 Join Date: Sep 2006 Location: lone pine and mammoth lakes Posts: 1,407	Re: LT5 technical problem Patrick, give Corey a call!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 2108676286

11-15-2006	#19
tccrab Join Date: Oct 2004 Location: Folsom CA Posts: 1,654	Re: LT5 technical problem 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 __________________ TomC '90ZR1 #792 Honorary Pirate [B]If it ain't FUN, you're doing something terribly WRONG. [/B]