so whats the deal here .. please anyone "throw me a bone or something" After all of these troubleshooting techniques, It boils down to ... Only start with starting fluid. Then it will stay on perfectly .. I can run it and turn it off and then turn the key to start it again and it starts just fine. If I let it sit for an hour or so or till the next day Forget it, I'll need to spray again.

whatcha think. I have no clue what the psi is at the fuel rail .. I hear the pump nice and perfectly .. I changed the fuel pump about a yr ago so its not that old. Fuel filter been changed. Plus I think I have a bad ground or something somewhere ... If I really let the motor get warm / heat up when I turn the key I get NOTHING at the start ..not a click nothing .. it must cool down to work again . Im starting to hate this car but I really love it since its a 91Z convertible.

thanks for your time
robert.

 

1St Problem Ideas:

Bad Fuel?
Coolant Temparature Sensor?
Throttle Body Needs Cleaning?
Plugs poorly gapped or just bad?

2nd Problem:

You're certainly aware that your VATS was modified to bypass the KEY chip resistor.
IS the resistance used well within the resistance Range of your Key? If you don't
have a chip key, unplug and measure the terminating resistance and determine if it fits one of the 15 Resistors found in the chart found here:
https://www.thirdgen.org/vats_passkey_system

If you're at one of the Maximum or Minimum of the chart then that could be the
problem. Try to get closer to the Design Resistance. If you don't have a VOM meter
you can get one for less than $5 at Harbor Frieght Tools.

I hope this is helpful.

 

very helpful !! thank you .. tell me something , How did you know my car was bypassed on the vats .. lol but its got some real nice pig tail almost dealer like installed .. it even has the #3 on it to tell you its the number 3 key. Would a bad or loose ignition switch cause this too ?

 

How did you know my car was bypassed on the vats

Incredible powers of deduction! ...............no.....I needed more info and
did a search of your previous post.

Another gentlemen had trouble with his Camaro starting and only running with
starter fluid....you may want to check it out. Particularly the end of post #7.

https://www.thirdgen.org/forums/tech...art-story.html

 

hey topfile thanks for your replies and for the links to the other posts. Wow what a detailed post. wish I was that detailed.

Well for one I know my ignition switch is somewhat loose/bad.. because there is some play when its on the ON position .. .. if and when I get the car started the windows will not roll down if the key is slightly pulled back just alittle but still on the ON position .. and when you put the key alittle bit foward .. waalaa the windows roll down. So I know the ignition is fubar. There are times when the car will turn over every so many times and then NOTHING just dead .. no crank .. but if I put he battery charger on it on low charge .. just to give it the ground and power it turns over just fine.

my ohms on the resistor reads 175 .. that falls within the numbers of a #3 resistor key .

 

Did you mean to say 675 ohms? The range for number 3 is 650 to 728 ohms.

Design resistence is 681 ohms for #3.

About it turning over sometimes: AS I understand if the Key Resistor looses contact with the VATS during driving the ECM sees it as a VATS Failure not as a theft attemp. In which case the ECM allows operation and starting of the Car. This operation is cancelled I believe if the Key is left in the Key On Engine Off position longer then 1 minute. I believe this is the operation haven't confirmed it though.

Does your Security Dash light Activate?

 

oops I meant 675... is that good enough to start everytime?

the security light goes out about 5 secs after the key is in the ON position.

 

675 sounds fine.

heat up when I turn the key I get NOTHING at the start ..not a click ...

Does the Security Light Act the Same way as you describe under this condition.
If it does I'd Check, Replace, or Bypass the Start Enable Relay. IF it doesn't VATS
was activated.

 

Oh yeah did you run your codes?

 

topfile.. how can I read the codes ?? do I have to buy that tool to read them and count the blinks etc.?? and the relay you talking about is that the one behind the drivers side kick panel? Im tired of bypassing things... I think your only asking for trouble down the road when you by pass stuff ..I've learned so much from this car .. She had some strange previous owners... I scratch my head alot of times when Im working on it and wondering why they did this or that.

 

Above the Driver's right leg should be a connector mounted to bottom dash panel.

You'll see two rows of connections.

You'll need to concern yourself with only with the top right of this connector
more specifically the last two pins on the top row.

Using a paperclip or some other wire connect these two pins together.

Get pencil and paper to record the blinks on the Check engine light

To begin the test move the Igntion to Key-On Engine-Off position. The car will run a auto test as you'll hear your fan activate.

Blink... Blink Blink = 12 This code starts and ends the test.

You may or may not get other codes following this code.

If you get code 46 I think that's a VATS malfunction.

Once it's finished turn the ignition off.

You don't need ot start it just key on to start the test and Key off to end it.
Remove the wire.

Report your codes.

Concerning the Start Relay Bypass option: This is only there for VATS. Since you've
already have VATS bypassed partially it should be no big deal. Otherwise, I'd find a replacement or troubleshoot the circuit.

 

Copy !!

I will try that when I get out of work today .. I need to go in now but get out at 5:30pm .. I will report my results later. thanks for all your help .

 

OK I ran the codes and here are the results ....

15 Low temperature indicated at engine coolant temp sensor

23 Low temperature at manifold air temperature sensor OR Throttle position sensor error

43 Low voltage at electronic spark timing circuit


I have no clue what an air temp sensor is or where that is .. And where exactly is the electronic timing circuit. ??

 

Here's the connector you'll need to locate.

Connect A to B.

http://www.austinthirdgen.org/mkport...ages/gmobd.gif

 

what engine you have and what year?

 

Code 43 could be a problem with the Ignition Module found under your Distribitor Cap.

You'll need a 5.5mm socket to get to it. Autozone carries the socket. Disconnect
plug wires 1-4 (driver side) on top of the distributor and note where they go
back!

Using the socket loosen the two screws holding down the Cap. Move the cap to the
passenger side of the engine. Locate the module under the Rotary Button. It has two
visible connectors, disconnect them. Remove the two screws holding down the
module with your new socket. Carefully rotate the module towards the passenger
side to reveal a third hidden 2 pin connector on the back of the module. Release this
connector. It goes to your pick-up coil. While you're there, measure your pick-up
coil. It should measure ~850 ohms (600 to 1500 allowed I think).

Now you'll notice the Module has a Silcone Grease on the back to facilitate thermal
heat sinking. You need to re-apply this upon reinstall. Scrap it off with a razor and
save it for later re-application, otrherwise buy more if you can find it.

Take the module to Advance for testing. Have them test it several times. If it fails
get a Module made by Standard (Standard Motor Parts).

When you reinstall it apply the grease. Also, make sure the Distributor Cap is
PROPERLY seated in the groove surrounding the first two connectors of the Module.
DON'T tighten until the Cap is seated and feels right over the module as you
can damage the module.

I'd also replace the ECT sensor found on the front of the engine under the
throttle body. I'd also get the Standard Motor Parts part as it already has
the conductive sealent applied to the sensor. Just take the old one out and replace.
This should clear code 15.

I'd then clear the codes by disconnecting the battery neg for several minutes.

Keep your fingers crossed.

Check the codes in week and if you get code 23 consider replacing the TPS.

Ultimately you need to clear these codes.

 

Hey Topfile thanks for all your help / replies and your time you have spent answering my questions.. You are a big here to me and other members of this board and its good to know that there are Knowledgeable people out there that can help out.! wish I could do the same . I could help you fix your Plasma or you LCD if it gives out .. LOL

but hey, I had already taken my module to oreileys to have it tested and they said it was good .. got all 5 green lights I told them to run it again .. they did .. same results all 5 green .. they said if the run it again it might get hold and might throw a red light on one of the spots... I purchased new termal compound and installed back on car...there is a center shaft there under the cap that looks like a star and it was kinda rusted with alot of surface rust, with a wire brush I brushed it good and blew away remaining rust dust.but I did this well before I had even posted problems on here about my car. and the battery was DEAD so I know the codes were cleared prior to the install.

if anything I think the battery wire that runs to the starter is cheap. I have a feeling it is not allowing much juice to run to the battery because after a few cranks the starter clicks rapidly like its running dead. But I've got an red top Optima and I know I've got plenty of juice. its not the starter because I've replaced it with a stronger one and same results. If I didn't love this car so much I swear I would just sell it .. but just knowing that they only made 3,203 1991 Z28 convertibles that year stops me. How many are still on the road today ??

thanks for all your help.. can I PM you if I have a problem later on. ?


BTW Chevy .. I have a 91 Z28 , 305 T.P.I. Automatic. "wish it was a 5spd" !!

 

ok, this to me is a voltage issue, pull your hot lead battery cable and clean the contacts on BOTH sides then tighten it down WELL, also the contacts of the rest of the balers leading to your starter, then try it, though your battery cable is probably internally corroded and needing relacement, do that and i think you will run fine, id chase the CTS and MAT sensors AFTER that, replace that cable or at least clean and tighten it, that goes for grounds too!

 

Only start with starting fluid. Then it will stay on perfectly .. I can run it and turn it off and then turn the key to start it again and it starts just fine.

I put this together for someone else who has a similair problem.
You may want to consider it as well.

Check out this schematic of your 91Z 5.0L, click it to magnify.....
http://www.austinthirdgen.org/mkport...ine_wiring.gif
Notice the Fuel Pump/ OIL pressure Switch top center of the circuit.

What I understand is after 3psi of oil presure is established this switch
activates to supply power to your fuel pump in the tank (Fuel Tank Unit
sch. reference). However, before this occurs you hear the Fuel Pump
prime with the key on for a few seconds and stops. This is because the
Fuel Pump relay was activated to prime the the pump for starting. Once
accomplished the ECM turns the relay off to the resting position shown in
the Schematic. When you actually start the engine oil presure is
established and the Fuel Pump/Oil Pressure Switch turns on and runs your
Fuel Pump.

If the Fuel Pump/Oil Pressure Switch was bad your car may start but it
wouldn't run for long.

If However, your Fuel didn't prime then the car wouldn't start except with
starter fliud and then run only until Oil Pressure was established and the
fuel pump was activated.

Diagnosis: Intermittant Fuel Pump Relay contact or related wiring.

Consider it.

Also, I'd look into replacing the Engine Coolant Sensor as it's one
of main sensor informing the ECM.

Certainly you can PM. Good Luck.

 

topfile, Im an Ex GM tech, if his oil pressure switch were in fact faulty the car would at least kick and run on its own, which would mean his RPMS would be high enough to bring up his oil pressure to the point of hitting that relay. he has spark but no injection till the car is running on the starting fluid, ALSO he has a low voltage code as well as low temperture faults from other sensors, i believe his hot battery cable is NOT supplying enough juice to the system to initialize everything in the ECM, i think honestly once he gets the engine running on starting fluid and the alternator spinning at speed is when the computer gets enough voltage to wake up. your theory is not plausible, because even if the fuel pump was shut off, the injectors would not be, and the kick from the motor would be enough to start the pressure up and get her running.
not trying to flame you btw, but think through the sequence you have here. also your starting when hot issue is probably your starter getting heat soaked from your exhaust, you have headers?

 

Chevy8588- I didn't explain it well I suppose, but I wasn't suggesting the Fuel Pump/
Oil Pressure swith was bad. Just that he may be having trouble witht the Fuel Pump relay or associated wiring.

As I understand the Oil Pressure Swich takes over from the Relay once Oil Pressure is established. If however, the Realy contact failed wouldn't starter fluid allow time for the Oil Pressure switch to activate and supply power to the Fuel Pump?

 

got yah, he stated in his first post that is primes, and even so, with a bad relay, starting time only increses by a couple seconds, oil pressure builds fast in these engines, your will achieve about 20 PSI on the starter alone, it was designed as a cut off in an emergency, but also as a way to circumvent relay failure

 

Can you please help me out? I have a 1988 Trans Am that only starts up with starter fluid . I changed the fuel pump last year and the car ran great. Last week I went out to go for a drive and the car wouldn't start.. I turn the key and didn't hear the fuel pump. I gave it a shot of starter fluid and it stayed running. I also heard a hissing sound coming from the area of my gas tank. The car does not have a Vats systems. Any help?