AlHewitt
Well-known member
I just bought a 94-ZR1-LT5 with 22K miles. It's a great car, but I don't think it runs right. That is, I'm disapointed in the performance of this engine. I also have a 96-LT4 and that is the basis for my questions. The ZR1 is a beautiful car but I have no experience with this engine. I've owned the LT4 for 5 years and find it superb in driving torque, smoothness and acceleration compared to the ZR1! I realize that the LT5 is a different animal, it is a high RPM motor, but looking at the torque curves the LT5 at any given RPM appears to be more touquey than the LT4. Based on this I would expect the LT5 to pull as hard as the LT4 does, I don't think it does.
OK, all that being said here is the question. The LT5 motor has a hesitation in free revving from idle to WOT and is this normal for this beast? It is noticable in simple driving and very apparent when first starting when it is cold. It makes down shifting when I sometime like to double clutch it, ugly. Step on the gas with the clutch pushed in and it takes a long time to get the RPM up to say 3000. The LT4 does not behave this way, that is, the responce is immediate with that engine. Very crisp, it's right now! Below 3000 RPM this LT5 is a pig, however above 3000 RPM the LT5 is a monster, it does pull very hard in the higher RPM's, probably harder than the LT4 does. So am I experiencing is an engine with a long cam that has lously low end characteristics? If this were 1965 I'd expect that to be the case but any more Chev has figured out how to make these things run well at all RPM's. I thing so at least.
I'm hoping to get some suggestions from this group as what I might do to make this thing perform well in the low RPM's. Here is a list of what I have done so far; I've had the plenum off twice, I'm getting good at that, I have had the fuel injectors out and serviced, the secondaries were dirty but cleaned up OK, the primaries were TU (so I was told) and I've replaced them. So I have new primary and cleaned secondary injectors. I have replaced the spark plug wires, the ignition coils (4 of them), the plugs were reportedly replaced 1000 mles ago and they (AC41-913) look to be OK, i.e. they are not foulded with oil. I've had it to two different shops, a Chev dealer and a FI specialist. The Chev dealer said the fuel pressure is normal so I assuming the fuel pump(s) are OK but there is a Service Information letter called (SAG OR SURGE ON A LIGHT THROTTLE ACCELERATION #57-65-14 9/18/1995) and he sold me a new and improved E-PROM (chip I assume) #12528772. After installing the chip it runs lously! Back fires through the intake on hard throttle operation, hesitates much worse than before and makes a popping sound in the exhaust during deceleration! I put the original chip back in and I'm back to the original problems. I then took it to the FI guy who did the work on the injectors. With his hand held computer attached to the car (reportedly the same unit that Chev uses) he was able to look at many parameters. He says it checks out OK as in all injectors are working, the timing is fine, etc.. however with the engine running he pulled the spark plug wires off of each plug one at a time to see how it ran on 7 cylinders. A noticable stumble at idle occures when a spark pulg wire is removed HOWEVER when he removed #3 wire the engine quickly dies with a arcing sound coming from beneath the plenum! His call was a bad ignition coil. I replaced all four of the ignition coils and the same thing still is occuring! So I'm not sure that this is a problem or not.
Any ideas where to go from here? Thanks...Al
OK, all that being said here is the question. The LT5 motor has a hesitation in free revving from idle to WOT and is this normal for this beast? It is noticable in simple driving and very apparent when first starting when it is cold. It makes down shifting when I sometime like to double clutch it, ugly. Step on the gas with the clutch pushed in and it takes a long time to get the RPM up to say 3000. The LT4 does not behave this way, that is, the responce is immediate with that engine. Very crisp, it's right now! Below 3000 RPM this LT5 is a pig, however above 3000 RPM the LT5 is a monster, it does pull very hard in the higher RPM's, probably harder than the LT4 does. So am I experiencing is an engine with a long cam that has lously low end characteristics? If this were 1965 I'd expect that to be the case but any more Chev has figured out how to make these things run well at all RPM's. I thing so at least.
I'm hoping to get some suggestions from this group as what I might do to make this thing perform well in the low RPM's. Here is a list of what I have done so far; I've had the plenum off twice, I'm getting good at that, I have had the fuel injectors out and serviced, the secondaries were dirty but cleaned up OK, the primaries were TU (so I was told) and I've replaced them. So I have new primary and cleaned secondary injectors. I have replaced the spark plug wires, the ignition coils (4 of them), the plugs were reportedly replaced 1000 mles ago and they (AC41-913) look to be OK, i.e. they are not foulded with oil. I've had it to two different shops, a Chev dealer and a FI specialist. The Chev dealer said the fuel pressure is normal so I assuming the fuel pump(s) are OK but there is a Service Information letter called (SAG OR SURGE ON A LIGHT THROTTLE ACCELERATION #57-65-14 9/18/1995) and he sold me a new and improved E-PROM (chip I assume) #12528772. After installing the chip it runs lously! Back fires through the intake on hard throttle operation, hesitates much worse than before and makes a popping sound in the exhaust during deceleration! I put the original chip back in and I'm back to the original problems. I then took it to the FI guy who did the work on the injectors. With his hand held computer attached to the car (reportedly the same unit that Chev uses) he was able to look at many parameters. He says it checks out OK as in all injectors are working, the timing is fine, etc.. however with the engine running he pulled the spark plug wires off of each plug one at a time to see how it ran on 7 cylinders. A noticable stumble at idle occures when a spark pulg wire is removed HOWEVER when he removed #3 wire the engine quickly dies with a arcing sound coming from beneath the plenum! His call was a bad ignition coil. I replaced all four of the ignition coils and the same thing still is occuring! So I'm not sure that this is a problem or not.
Any ideas where to go from here? Thanks...Al
