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Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Originally Posted by Chimera96
if it is a "stock" rebuild it should run fine with stock programming.
If it won't run on its own you need to find out why. Motors with vacuum leak typically have a high idle
If your gas is crap, it should not be if the car has been sitting since June, adding some additive will not "fix it".
Doing a engine R&R there can be several things causing it not to idle. Maybe the IAC is sticking, could be anything.
Trying to log a new motor that will not run on its own while also going through all the initial motor start up stuff, bleeding the coolant, etc. and logging while the car comes up to temp it may show all kinds of "not ideal" readings. If it threw a code that could lead to some idea wtf may be going on. A 0300 code for example would me misfire but a engine not running right because, for example, valve lash is all F'ed up won't throw a code saying "your valve lash is screwed up"...it will just throw 0300 or some non related code because the motor is shiating itself trying to run. You need to methodically go through all connections, plug wire on correct, fuel pressure check. Those kind of things to see why your "stock" rebuild is having problems idling. From this side of the internet we can only guess based on your general descriptions. We can't hear what is going on or monitor fuel pressure, etc from our end.
Did you mean to say I probably don't have bad fuel? Is there a way to know other than draining close to 10 gallons out of the tank? I would prefer not to do that.
I went through all the connections, went thru shbox and double checked the harness diagram as well as looked for any leaks. I don't see any bad connections, nothing with the MAF, IAT, etc. All the spark plugs, plug wires, cap and rotor are new also.
I guess the next step is to get a fuel pressure gauge and monitor the pressure and see what's going on.
EDIT: I want to mention that the PCV hose that goes to the throttle body is cracked and I used Gorilla Tape to wrap it around multiple times. It seems secure but I thought I'd throw that out there in case that could be suspect
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Twice during my attempts to start the car the car abruptly lost all electrical power a second after it started up. I had to move to key to off and on back a few times and it came right back.
I'm now considering maybe it's a bad ground or vats? My security light has been on solid and the previous owner said it doesn't affect the driving but solid while driving means there's an issue somewhere.
Bad ground doesn't seem likely since the car doesn't lose electrical power randomly just when I crank it.
I already bought a pack of resistors to bypass the vats and I may just do that now to see if it resolves anything.
Kind of weird that it will start the car but will not stay alive..
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Originally Posted by ridiqls
Maybe it's entirely two different issues
I am a bit lost on what you did and what the problems are...but if this car has ? history you bought with a blown head gasket...likely several other "issues" going on. Tedious and difficult to diagnose and fix.
Since the VATS is in ? you need to resolve that in/out as the/or contributing factor. The later being difficult as if you do bypass it and it still does not start/run you now need to find the why for that. However you will at least resolved and eliminated VATS as being a issue if you are able to duplicate the resistor value to the chip on the key
Fuel pressure check is one of the very basic checks to rule fuel pressure in/out as a reason car won't start. You have a 20+ year old car which you will be better served if "you" can do diagnostics and repair...otherwise your wallet will need to be very thick
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Read Shoebox's PASS-Key (VATS) guide. It explains what the SECURITY light being on all the time means. Sounds like the system is in “fault enable mode”.
I'm pretty sure Chimera meant the gas needs to be replaced. Siphon the old gas out.... maybe it will work in a lawn mower. Put in 3 gallons of fresh premium grade fuel.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Originally Posted by Chimera96
I am a bit lost on what you did and what the problems are...but if this car has ? history you bought with a blown head gasket...likely several other "issues" going on. Tedious and difficult to diagnose and fix.
Since the VATS is in ? you need to resolve that in/out as the/or contributing factor. The later being difficult as if you do bypass it and it still does not start/run you now need to find the why for that. However you will at least resolved and eliminated VATS as being a issue if you are able to duplicate the resistor value to the chip on the key
Fuel pressure check is one of the very basic checks to rule fuel pressure in/out as a reason car won't start. You have a 20+ year old car which you will be better served if "you" can do diagnostics and repair...otherwise your wallet will need to be very thick
That video shows what is going on. Car will start, but will not remain running and will die a second after it fires up. Fires up every time. The reason why I thought it might be VATS related is because I also happened to have lost electrical power when the car dies a few times.
I just bypassed the VATS with the appropriate resistors and tried again few moments ago. The problem remains. Fires up, dies immediately.
The car was bought as a project car so I don't mind learning. I just went to autozone and rented a fuel pressure tester gauge so that will be the first thing I do tomorrow to see if I can narrow which part of the fuel system is possibly causing the issue.
Originally Posted by Injuneer
Read Shoebox's PASS-Key (VATS) guide. It explains what the SECURITY light being on all the time means. Sounds like the system is in “fault enable mode”.
I'm pretty sure Chimera meant the gas needs to be replaced. Siphon the old gas out.... maybe it will work in a lawn mower. Put in 3 gallons of fresh premium grade fuel.
I bought a siphon today so if fuel pressure testing doesn't show any faults, I plan on removing the fuel and replacing it
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Originally Posted by ridiqls
I am wondering if it is old fuel. I didn't do anything to stabilize the fuel because I hadn't foreseen how long the car's rebuild would take. It sat without a start since early July of this year but who knows when the previous owner originally filled it up with gas. So about 4 months. I unfortunately don't have a fuel pressure gauge but I could buy one if I can't fix this simply.
As I mentioned I was getting a little lost in what your issues are.
My earlier comment about fuel was assuming the gas was no more than 4 months old. Your post above says July which makes that 4 months unless the gas was in a non running car before you got it for "X" more months. IDK how much ethanol you have in your gas there but I have stored gas I rotate every 6 months in my DD. My SS I have had gas in tank for 3-4 months without a problem.
IDK how old gas has to be to not even start a car. As Injuneer notes it would be good to at least drain 3 gallons and add fresh if you gas smells foul. In my experience I have and do store gas in 5 Gal cans I keep for emergencies that I rotate every 6 months in my DD vehicles and never had a problem and have been doing that for decades
If I understand you correctly the car does not even start now, but did. I would check FP.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Originally Posted by Chimera96
As I mentioned I was getting a little lost in what your issues are.
My earlier comment about fuel was assuming the gas was no more than 4 months old. Your post above says July which makes that 4 months unless the gas was in a non running car before you got it for "X" more months. IDK how much ethanol you have in your gas there but I have stored gas I rotate every 6 months in my DD. My SS I have had gas in tank for 3-4 months without a problem.
IDK how old gas has to be to not even start a car. As Injuneer notes it would be good to at least drain 3 gallons and add fresh if you gas smells foul. In my experience I have and do store gas in 5 Gal cans I keep for emergencies that I rotate every 6 months in my DD vehicles and never had a problem and have been doing that for decades
If I understand you correctly the car does not even start now, but did. I would check FP.
Yep, it was a running car before the old engine got pulled. The new engine is in and I went through and double checked all the connections, vacuum, etc. and it is firing up and dying abruptly.
I will check Fuel Pump tomorrow.
I'm reading through a lot of old threads and also shbox and will explore the possibility that it is VATS related. I did bypass the ignition key but apparently that signal goes to the BCM and then the BCM goes to the PCM. I'm reading a lot of folks who had their car start and then abruptly die just like me because of VATS. The PCM turns off the fuel injectors if it doesn't get a signal from the BCM. In this case, you have to get bypass the entire system and not just the ignition apparently..
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Your 94 does not have a BCM. Only 96 and newer. As clearly described in the Shoebox writeup, and shown in the system wiring diagram he links, your car has a theft deterrent module. Same function, but if you go looking for a BCM, you're not going to find it.
There is an aftermarket gadget that will supply the 50 Hz fuel permit signal to the PCM, bypassing the VATS interlock for fuel.
The VATS system does not cut off all power the car. It interrupts the starter solenoid circuit, and prevents fuel flow.
If you are losing all power with thekey in the “start” position, could be a problem with the ignition switch, not uncommon in these cars when thy reach 20+ years of age. Shoebox has info on that too.
Last edited by Injuneer; Oct 26, 2018 at 10:11 AM.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Originally Posted by Injuneer
Your 94 does not have a BCM. Only 96 and newer. As clearly described in the Shoebox writeup, and shown in the system wiring diagram he links, your car has a theft deterrent module. Same function, but if you go looking for a BCM, you're not going to find it.
There is an aftermarket gadget that will supply the 50 Hz fuel permit signal to the PCM, bypassing the VATS interlock for fuel.
The VATS system does not cut off all power the car. It interrupts the starter solenoid circuit, and prevents fuel flow.
If you are losing all power with thekey in the “start” position, could be a problem with the ignition switch, not uncommon in these cars when thy reach 20+ years of age. Shoebox has info on that too.
Thanks for the correction, sorry I meant to say TDM.
I've been trying to troubleshoot this all day and I'm at an impasse.
So far I have:
1) Tuned out VATS - Just wanted to eliminate the chances the PCM is cutting fuel from the injectors.
2) Bypassed VATS under column using resistors.
At this point, the car cranks and Security light is now gone so vats is eliminated as a possibility.
3) Cleaned ALL battery terminals including the ones that bolt to the body of the car. Cleaned all ring terminals, checked 12v and ground at both, as well as ground on the passenger side motor mount stud.
This got rid of the electrical power cutting out. Eliminated that as a factor.
4) Hooked up a fuel pressure gauge.
Key On Engine Off - 43 PSI, no leaking. I left it for 30 mins + and the pressure has not gone down.
When I start the engine, the pressure drops to around 33 PSI, maintains until car dies few seconds later. When car dies, it returns back to 43 PSI.
I am going to buy starter fluid and if the car stays alive, then we know that it is a fuel problem and nothing wrong with the pressure, which would point to bad/old fuel.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
FP is good. Injuneer is way more qualified than I am to discuss/review any data log
I would think if the car starts the fuel in it would be good enough for the motor to continue to run. You could drain out some and add new gas to see if there is any improvement
Your work today at least eliminated VATS, FP and battery ground as suspects.
One ignition item that is known to see a car start then shut off is the ICM...but generally the car will not restart. However I did have one fail that exhibited none of the usual symptoms like that. Car would always restart but I had to spoon feed the gas pedal to keep it running which is a symptom not generally associated with a failing ICM. Since I had a old known good spare I swapped it in and bingo all is good. Auto part stores have a way of testing them but often they fail when hot so they "bench test" good.
Anyway not saying it is your ICM...but until you find the "why", it's on the list of possibilities
Ideally data log will reveal a clue Injuneer can assist you with
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Oh man, the problem is solved and the car is now idling!
I had someone suggest to unplug the MAF sensor. It idled right away. Apparently if you unplug the MAF sensor, the car runs it from a memory bank somewhere enough to get the car to a service center.
Wow, I was troubleshooting everything. I'm never forgetting that one for the future
Time to bleed the coolant and datalog it for real to see what the PCM sees for temps.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
When you disconnect the mass air flow sensor, the PCM defaults to speed-density mode. It can calculate the mass air flow from the manifold absolute pressure (MAP), absolute inlet air temperature, (IAT), engine RPM and a stored table of volumetric efficiency (VE).
Dropbox requires an account to download the file. Just upload to this site it in a post. “Go Advanced”, “Manage Attachments”.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
Still riding on that high from getting the car to idle. I was concerned I had to drop the tank and do a fuel pump job.
I went to clean the MAF and look at what I found: Intake Underside Split Open, not visible and actually can't even feel it when it's aligned
Right in front of the MAF. The entire rim of the plastic is rotted away and crumbling. I had to cut it out and trim it back about 1/2" with a dremel and I gorilla taped it like crazy. Will be replacing the intake in the future anyway
Injuneer, I'll attach a new data log tomorrow that I'll run while I bleed the cooling system and check temps. Really interested to see what this car will do with the cooling fans.
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
If that crack is "before" the MAF it would not matter much other than unfiltered air entering engine...if after than it is "un-metered" which will certainly mess up air/fueling
Re: Looking to buy a 94 Z28 with head gasket problem, what to look for?
That looks like the pre-MAF intake ducting. It could have caused a really dirty MAF.
You can by cleaner at the parts store for the MAF, but will need to remove the screens to clean it. Be EXTRA careful with the spray and a q-tip, then let it dry for 10-15 minutes before reinstalling.
