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Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
people have used the appropriate size deep socket or even the splined coupler to install these seals. IMHO you want a tapered end so the seal can initially slide on without folding the inside lip over which is why I use the one shown. Also goot to slightly rotate seal while installing it on the tool. Once seal is on tool you place over spline drive gear end and push flush with your fingers then use a deep socket the size of seal to go over this tool and tap the seal in with a hammer against the deep socket.
Kent Moore made a plastic version for GM to use. It is insane $ to buy but it came with the Kent Moore hub install/removal tool I bought several years ago on ebay. Those to are very high $ but back then I got it for a decent $50 IIRC
When the LT1 was assembled the seals were put in the TC first. The tool was then just put over the WP drive spline and the TC with seals was placed over that and bolted to motor.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
I just changed out my timing cover gasket and all 3 front seals. I have changed the water pump drive seal before (10 years ago) using a sharpie. I couldn't find one this time so I ordered that tool and it made putting the seal on pretty easy. I have a few hundred miles on the car since then without leaking a drop of oil. Hopefully it stays this way. It seems like my car has always dripped a little bit of oil over the 14 years I've had it.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
This is a review of your first data log. My intent was to walk you through the most meaningful columns. Many of the column do not apply to idle. And I noticed with a quick look at your second log that some of those results are different.
Date and Time (of day) are obvious.
Scan Time isn't really important.... engine run time is.
RPM - as you can see, with the engine not running, data shows as 45 RPM - Normal. As the starter cranks the engine, RPM rapidly picks up. Engine strated in 1.25 seconds.... good.
RPM Variation shows the departure of the actual RPM from the Target RPM. Only becomes meaningful when there are major difference.
A/C Pressure - ignore if A/C not "on"
Target Idle Speed is what the PCM is trying to control the engine RPM to. As you can see, the number starts higher, and drops as the engine warms up. There is a table in my scanning guide showing target RPM vs. Coolant Temp. Once your engine warms up, the idle, compared to the 800 RPM target is very stable. 800 RPM is the number for an M6 transmission. (I think you need to set up a signature - I looked back but forgot what trans you have.
IAC Position normally goes up at cold start to maintain the higher idle speed. Yours comes down to 44 at full warmup... a bit outside my recommendation of 20-40 counts, but in the next log it seems to be within those limits.
Minimum IAC position is (I think) just n indication of where the PCM parks the IAC motor at shutdown).
Coolant Temp and Intake Air Temp are obvious. Your CLT seems normal, maye a bit slow to warm up. The IAT should be close to ambient outdoor air temp. I would assume you had your hood open, because the IAT elevates very little as the engine warms up. With the hood closed, you can see IAT 10 - 20-degF above ambient air, due to heating of the intake duct and heat soak of the sensor.
EGR shows the duty cycle (% open) of the EGR vacuum solenoid. EGR is not used at idle.
Speed - car was standing still
Engine Run Time is obvious. I always look around 206 seconds to see if that is when the PCM transitions form open loop to closed loop. That is the "timer" function, which is only one of three items that have to be met for transition to closed loop. Others are coolant temp and both O2 sensors "Ready".
Ignition Volts - This is the voltage read by the PCM at the power supply terminal. The 8.5 volts while cranking looks weak, but the alternator props it back up to mid-13's rapidly.
Barometric Pressure is the pressure of the air column pushing down on all of us. Looks like you are located near see level, with a high reading. That's good.... high pressure means denser air, means more HP
TPS (throttle position sensor) volts are within spec. The PCM looks at the TP sensor at startup, and sets that voltage as 0% throttle opening, as long as the value is between roughly 0.25 - 0.85 volts.
TPS % shows throttle is closed.
MAF air flow in grams per second appears normal for an engine idling at 800 RPM
MAP (kilopascals) is normal for idle, indicating very good intake manifold vacuum (MAP - Barometer = vacuum). New engines will do that.
MAP volts is what the PCM sees from the sensor, and converts to kilopascals
A/C Pressure and Temp were ignored since system not in use.
Spar Advance is normal for stock programming at 800 RPM idle, ranging from 18 to 23 degrees advanced
No Knock Retard is normal. Seldom seen at idle unless there is a major problem.
Knock Count are "elusive". Knock Counts can increase when there is no knock retard. and there can be knock retard when knock counts are not changing. Counts field simply increments upwards until it reaches ~64,000, then resets to "0". The absolute value means nothing, only how fas it is increasing.
EVAP purge solenoid duty cycle - not used at idle.
BLM Cell # is at 16 for the entire log. That is where the long term fuel corrections are stored for idle.
Left and Right O2 sensors start around 0,450 volts, since that is the bias voltage the PCM supplies. The O2 sensors have to warm up before they can start to add to, or subtract from the bias voltage. As they warm up, the readings increase slightly, and then start to drop as the PCM reduces the cold start A/F ratio, and the effects of the raw oxygen in the air from the AIR pump kick in.
Long Term Fuel trims start at 128 after a PCM reset. They stay ther until the PCM kicks into closed loop. Then the PCM uses the short term fuel corrections to toggle the O2 readings back and forth between rich (above 128) and lean (below 128), which is required for the cat to work. If the PCM sees the short rems are staying mostly on the low/lean side if 128, it will increase the long term correction to richen the mixture. You can see that happen on the left bank, right after it goes into closed loop. No bidg problem here.... 130 left / 128 right indicates the PCM is getting the A/F ratio right with minimum (left side) or no (right side) corrections. This is excellent, but I noticed it does change in the second file.
Gotta take a break as this point.... I'll cover the rest of the columns in another post. Still looking at log #2.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Thank you so much for the explanation, that's really what I needed so I can learn and retain this info for the future.
I'm glad you mentioned it because today, I took a quick drive to the gas station to fill up the tires and got stranded.
The car is having an issue where if you drive it and it warms up, and then you turn it off and try to restart it, it will have a very weak SLOW crank. It will not start back up and I have to wait 10-15 mins before I can get it to start up again. Even on a cold start up, it does take maybe 3 full Mississippi seconds to start.
Note, it's a slow crank meaning it will crank....pause, crankkk.... pause.... crankk pause.... and then "catch" to start the car up. Not a consistent crank, crank, crank, crank.
This was an issue with the old engine so it's not mechanical.
But I noticed you wrote this: "Ignition Volts - This is the voltage read by the PCM at the power supply terminal. The 8.5 volts while cranking looks weak, but the alternator props it back up to mid-13's rapidly."
So is this indicative of a weak battery? Would this be an indirect way of load testing the CCA on the battery?
If I'm not mistaken, I think you want at least 9 volts when cranking right?
I'm trying to figure out if it's the battery or starter.
- Battery is dated June 2017 so it's not that old.
- Voltage measured at 12.37 when I got back home after being stranded
- Lights on the dash dim when I try to start the car
- When doing my compression test, the Starter had no issue with cranking. It was cranking at a very normal, fast cadence. Same situation when I also used it to prime the oil pump on the new engine. It is however a different result when actually trying to start the car up.
So ... after what you provided about Ignition Volts, I'm leaning toward a weak battery.
I had the battery tested at Autozone and they said it was good which is why I'm confused. She just showed me the screen that said 100% charged, I don't think they did a load test on it.
Video of me trying to get the car started back up at the gas station parking lot: https://imgur.com/GYTgOLa
Pretty sure its the matter now that I'm paying attention to the volts dropping so drastically. thanks for pointing that out. I'm going to autozone again to see if I can get a replacement
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
I looked back at the log. Appears the start procedure may have lasted closer to 2 seconds. The PCM is seeing 12.1 volts, and stable. Assume nothing is happening. Over a period of 0.36 seconds the voltage drops to 11.7 over 3 frames of data. Then in the next frame, 0.14 seconds later, the reading is 8.7 volts. That's probably when the starter motor statrted drawing current. Elapsed time exactly 1/2 second. RPM is still reading 45.
At that point there's a significant inrush of current, which could result in lower voltage. Over the next 5 frames of data (0.6 seconds), the voltage is:
9.5
7.7
7.2
7.2
8.2
....and the RPM is still at 45.
Next frame the RPM has risen above 45, and the readings, about 0.14 seconds apart are:
This is interesting. I’ve never had any reason to look at the starting process in this level of detail. I wish I had this software 20 years ago so I could have saved the records of what my Formula did, and could relate first hand to what it sounded like, when it was still “stockish ”.
After I had the stroker built, my starter (stock replacement under warranty, with about 30,000 miles on it) was struggling, causing extended cranking. My thinking was OK, this is the result of the heavier parts and higher compression on the stroker. But the shop told me they measured cranking torque and it was less than my stock engine. Figured that 30,000 miles being toasted by my shorty headers might have damaged the starter. I bought a CVR Pro-Torque starter, that could be rotated to move the solenoid away from the headers. The difference was amazing. Just like when the car was new..... turn key, engine starts immediately. The electrical drag of the starter, dropping the voltage (car had a brand new AC Delco Professional Battery) had been affecting things like the injectors and making the engine hard to start.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Originally Posted by Injuneer
I looked back at the log. Appears the start procedure may have lasted closer to 2 seconds. The PCM is seeing 12.1 volts, and stable. Assume nothing is happening. Over a period of 0.36 seconds the voltage drops to 11.7 over 3 frames of data. Then in the next frame, 0.14 seconds later, the reading is 8.7 volts. That's probably when the starter motor statrted drawing current. Elapsed time exactly 1/2 second. RPM is still reading 45.
At that point there's a significant inrush of current, which could result in lower voltage. Over the next 5 frames of data (0.6 seconds), the voltage is:
9.5
7.7
7.2
7.2
8.2
....and the RPM is still at 45.
Next frame the RPM has risen above 45, and the readings, about 0.14 seconds apart are:
This is interesting. I’ve never had any reason to look at the starting process in this level of detail. I wish I had this software 20 years ago so I could have saved the records of what my Formula did, and could relate first hand to what it sounded like, when it was still “stockish ”.
After I had the stroker built, my starter (stock replacement under warranty, with about 30,000 miles on it) was struggling, causing extended cranking. My thinking was OK, this is the result of the heavier parts and higher compression on the stroker. But the shop told me they measured cranking torque and it was less than my stock engine. Figured that 30,000 miles being toasted by my shorty headers might have damaged the starter. I bought a CVR Pro-Torque starter, that could be rotated to move the solenoid away from the headers. The difference was amazing. Just like when the car was new..... turn key, engine starts immediately. The electrical drag of the starter, dropping the voltage (car had a brand new AC Delco Professional Battery) had been affecting things like the injectors and making the engine hard to start.
This is super interesting. So I went to Autozone and they replaced my battery for free under warranty. It's got 875 CCA and a full charge.
And as expected, first start cold it starts up. Still slow though, took about 5 seconds this time. Then I went for a quick drive, got the car up to temp and came back home. I turned the car off, and then started to datalog and tried to start up the car again now that the car is warm. Does not start.
The ignition voltage starts at 11.6 and when I try to start the car, it drops to 9.0, then 8 and then all the way down to 6.6 and hovers around 6-8 for a while as it tries to fire up the car.
As I'm trying to crank, all the lights on the gauge cluster and the dome lights start to flicker and dim as it seems like the car is struggling to get the car started.
If you have a bad starter, is it possible that it would put such a load or draw on the battery that it would cause that?
I can replace the starter but before I go ahead and get one, I'm trying to rule out anything else electrical.
ICM and Coil, I'm still unclear how they work and whether or not I need to consider this as a potential cause of this problem.
Injuneer, in case you wanted to take a look I attached the datalog of the warm crank after I got back home from the test drive. It's about 50 seconds and most of it is just me trying to crank the car in the beginning. No pressure to spend a lot of time breaking down everything unless you feel like it.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Don't know if they have the starter's expected amp draw in the factory manual. If they do, and you can borrow a clamp on DC ammeter, it might show if the starter is drawing high amps. Might be worth reviewing the starting section of the manual.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Originally Posted by ridiqls
Yep the cables are original.. they look good but I might replace them. I'm down to either doing the starter or battery cable or both
20+ year old anything on the car may need attention. Battery cables being one of them.
If your motor is rebuilt with higher compression than stock the original starter can have difficulty especially when that motor is at operating temp. Certainly if that starter is defective....or the battery cables are crap.
Many of us switched to the Corvette starter at autozone. It is a gear reduction type vs the stock one, smaller and cheaper than stock starter. When I went 383 my original starter, with engine hot, would struggle. Vette starter has been in for years now. Auto zone will want a core....so you might want to return your core a few days later as it won't look like the vette starter
I would also confirm you have a ground strap from rear of motor to fire wall
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Starting my car would be intermittent. Turn the key start fine, next time turn the key and nothing would happen. Wait a few minutes and try again and the car would start. I didn't think that would be the starter but it was. I upgraded to the corvette starter and it has never happened again.
I have also upgraded my battery cables too (this was a few years before the starter upgrade). The cable between the alternator and the battery went bad, when everything got hot the resistance would go way up and my battery wasn't getting charged. This would show on my gauge by going down to 8 volts. Jump start the car when cold, gauge/battery would read 13 volts until it got hot again. I would recommend upgrading the cables to anyone. Don't remember where I got them from though.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Chimera, I don't recall a ground strap from the rear of the block to firewall. I don't think there was one when I removed the engine either. Which one are you referring to?
I have the ground strap on the driver's side they goes to the ICM. Then there's one on the battery harness that goes to the passenger motor mount stud.
And then another small one for the PCM that mounts from the harness to the side of the passenger block stud near the knock sensor
I can't find battery cables anywhere that don't cost like $120+. I think I will make my own. I think the wire gauge for they terminal are 2/0 gauge?
10-31-2018, 11:48 AM
