91REDZ28VERT

Hello all, I have a 91 Z28 5.0 TPI convertible that I parked for a few years( 2yrs. approx.)...... I know, I know (didn't even treat the fuel). I drained the fuel tank and put fresh fuel and a new battery in it. I put the key in to start it, it turns over (approx. 150 rpms) then jumps to 400 rpms or so then drops to 150 then back to 400. it does this back and forth for as long as I turn it over.


So I searched the web/forums and began testing everything I could find info on...... TPS is good (from .30 to 4.53v wot) , ICM tested good (tested several times) pickup coil is good (790 ohms constantly), the coil is good (I also checked to make sure it gets 12v) so then I checked spark and its good. as far as I can tell the ignition system seems fine.


So next I have my wife turn the key while I listen at the rear of the car and I can hear the pump working, I go to the valve on the fuel rail and there is pressure, so I went to the parts store and barrowed a fuel pressure gauge. it was at 40-42 with the ignition switch on and jumped to around 50 when I tried to crank the engine over. so its getting good pressure.


Next I sprayed fuel down the intake turned it over fired up then died. So I am thinking its the injectors are not working. Set my multi-meter to 2k ohm, #3 read 12 and #7 read 6 the rest read 17. I checked each injector plug one at a time had 12v to both wires (except 8 it had 12v to one wire). I disconnected all of the injectors and checked the plugs and got 12v to one wire but as soon as I connect one injector both wires on all plugs get 12v.


I am thinking the injectors all went bad from sitting with fuel in them but I don't know..... I ran out of searches so I decided to register and post this. I appreciate any help Thank you.


the car has 32k original miles and has been garage kept, so no corroded wires or plugs it ran very well until now. I know its my fault but I had several unfortunate events take place and that's why I let the car sit without starting/driving for so long. BTW this is my first post so sorry if its too long.

1MeanZ

iTrader: (9)

I believe what you are seeing voltage wise is normal. next two prime suspects in my book are the ECM fuse and the VATS module. With key on you should have the check engine light. If you don't the ECM is not getting 12v and won't fire the injectors. Do a search on the VATS module as well. I don't know how to trouble shoot them because I just eliminate them from the chip on all my cars.

91REDZ28VERT

Thanks for the reply, I would like to eliminate the vats since I hear they can be troublesome....... How would I eliminate the Vats?


The check engine light is on when I turn the key and crank it over. Does that eliminate ECM as a suspect? If not can it be Tested/Checked?


Thanks

91REDZ28VERT

It turned out I had 5 bad injectors, I called Southbay and ordered new ones, once installed ( a week ago) it fired right up. Thanks South bay!!!

Hawgtied

Thanks for posting this. I am having similar issues with my car. I haven't eliminated the fuel pump just yet. But it is getting spark and thee is some fuel pressure at the Schrader valve on the fuel rail. I'm picking up a gauge today and will see what the actual pressure is. My car also sat for an unknown period of time. Judging by the title, it has sat for at least four years.

1MeanZ

iTrader: (9)

I believe both of you guys' cars had the later style Multec injectors from the factory, which are known to be problematic. I had a set one time that would start and run just fine, but once hot they would stop pulsing and shut the motor off. That was a challenge to diagnose!

Moral of the story is, if you have the Multec injectors, replace them, period.

91REDZ28VERT

Although mine is still not running right, I started another thread about that issue .... it stutters to accelerate and feels like a V6

Hawgtied

I checked fuel pressure yesterday and with the key on, after the pump primes, I show 43 psig on the rail. Next I will get a fresh battery and try to crank it a couple times and what happens. I am now highly suspicious of the injectors.

91REDZ28VERT

I put a fresh battery in mine and it would "want" to start but would not. So I sprayed fuel in the intake just to make sure everything else was working and had a noid light in a injector terminal. I would get a signal at the terminal and it would fire right up. So that was enough for me to order a set of injectors.

Hawgtied

Excuse my ignorance, but I've read it a few times and I'm still scratching my head; What is a noid light?

Bob88GTA

iTrader: (2)

Tool set for checking the presence of on-off signals at electronic fuel injection components. Little lights that connect to your injectors for checking pulse

Hawgtied

Okay. Thanks!

91REDZ28VERT

Hawgtied, Any updste?

Hawgtied

No, no updates yet. I was on yard duty this weekend. My VATS bypass should come in today and I'm picking up a new battery as well. I got my fingers crossed that it will start. If it does start, I will likely replace the injectors anyway just because I'm sure they will need cleaning and since I have to take it all apart, I may as well replace with better parts. I'll update with any breaking news!

Hawgtied

Eliminated the vats with a bypass. Installed the new battery and tried to crank. I actually got the car to run but it was definitely not right. Sounded like it was running on four cylinders. Unplugged the injector one at a time and got the same result. Checked the firing order and traced plug wires out just to eliminate that. Pulled cap and rotor and all that looked good. So now it sits with the plenum and runners removed and the fuel rail and injectors out. I guess I'm gonna be contacting Southbay for a set of 22#'s. Meanwhile, I guess I could polish all that mess since it's out of the car!

Hawgtied

Replaced the injectors with new ones from South Bay. Runs better but still won't idle. Also I noticed a big fuel leak running off the back of the motor. So now I have to take all that stuff off again to see what is leaking. I suspect the injector o rings or the crossover tube o rings, but what do y'all think if the diaphragm was ruptured in the FPR?

Bob88GTA

iTrader: (2)

did you follow the directions of installing the injectors into the manifold first, then into the fuel rail?? If not you may have a leak with that.

A ripped diaphragm will send fuel into the plenum then down the runners, then into cylinders. Crossover tube o-rings may be bad.
Remember........fuel on top of HOT intake is NOT GOOD. I'd get that taken car of. Just turn the key on and let it pressurize the fuel rail and look back there for leaks. If the o-rings are leaking, you'll see it

Hawgtied

I'll have to pull the instructions back out for the injector installation, but I thought they went into the manifold first and then the fuel rail goes on top to hold them down. I did lube the O rings with dish soap as suggested. I think I'm gonna pull the plenum so I can see better and then cycle the key to check for leaks. Definitely not going to try to start until this is resolved. The car was sitting in a huge puddle of gas with the starter just inches away. I could have burned the car, my garage and house and myself to the ground-not good. Thanks for the input.

Bob88GTA

iTrader: (2)

"manifold first and then the fuel rail"

That's what I meant, sorry,long day! I changed it above.


As per SouthBays instruction:

"The complaints that we have received throughout the years with the bosch lll's is that fuel leaks from up top if the injectors are installed into the rail first and that's an installation or an oring issue. We have found that when they are installed into the intake first it alleviates all leakage from the rail side, has to do with alignment. The reason why the oring is square is that we have them custom made for our adapter and for proper fitment. When we first designed the adapter for the bottom of the injector we did R&D for about 6 months to make sure fitment was perfect before we started selling them. They are specific for the adapters and yes you are correct, they don't sit as far down into the intake as the stock, but it is ok. Guarantee you will not have a vacuum leak. Will tell you that the injectors will more than likely leak if they are not installed properly."

Hawgtied

That's good info to have. Hopefully I can pinpoint the source of the leak. I can see it dripping down the back of the motor on the driver's side.

dtees

1meanz Thanks for your comment about multec injectors. I have a 90 tpi vette. Starts and runs ok. When it gets to operating temp the car wont start. A real pain with the 6 speed if you happen to not operate the clutch properly. After the car sits for 30 min it starts just fine again. I'm going to try the FIC bosch gen III injectors. I am a professional tech and installed some in a customers TPI 5.7. The engine ran terrific. I removed accel injectors. I haven't read up on vats lately. I'm pretty sure it just keeps the starter from operating. When my vette won't start I have injector pulse and good spark. I used a noid light to check injector pulse. I guess the pintle inside the multec injectors sieze when the engine gets hot. I agree with you. Anyone with multec injectors should get rid of them.