topfile

I'm going up Saturday to try fixing it.

Here's the story. After much searching My Daughter had to have
a Third Generation Z28 to take with here to college this semester.
She bough it after it had been setting for several months.

It's a 5.0L Automatic 1991 Z28 with 170,000 miles. Previus owner
never took it more than 40 miles from home and stayed off the interstate.

To get it ready for the 200 mile run to School
I did the following over the summer:

-Cleaned Throttle Body
-replaced all vacuum hoses I could find
-Had Valve Stem Seals (Blue Smoke at Start-up) and Plugs (AC DELCO) replaced a week ago.
-Came with new plug wires
-Replaced both Air Cleaner and PCV
-Replaced Struts and Shocks with KYB
-Ran Sea Foam with a full Tank
-replaced old OEM O2 Sensor with Bosch
- Changed OIL twice in 1000 miles, presently running Shell Rottela T
10W 30
-Replaced all Coolant and Flushed


What Happen.... Made the trip fine to school. Blew smoke when she punched it up the mountain.
Other wise no problem. Noticed it hard started when warmed up. Took two or three attemps at cranking before
it started. I left and went home think it'll be OK.

Last night she calls and it's not starting after sitting for 5 hours after
a 5 mile trip. Tried troublesooting it remotely as she's 200 miles away.
Been driving it for a week.

I've talked a Mechanic. I told him the symptoms:

- Was Exhibiting Hard start when warm.
- Runs with Starting fluid then dies
- Cranks but won't start
- Can hear the fuel Pump Prime with ignition on
- Tank is full
- Recently Set code 32 (EGR valve) on long cruising speed trips more
than 100 miles
- Recently had valve stem seals replaced

I let him talk before telling him my ideas. He told me since the engine
actually did start briefly that the Ignition System was likely OK,
and was likely a fuel delivery problem. However.....

He was thinking the following

-Fuses: Check Ignition 1 and Ignition 2 fuses if his memory serves.
Verify relays are fully connected. They may control the activation of the
the 8 Fuel Injectors on top of the engine. IF the injectors don't turn on no start will occur.

-Relays bad: At fire wall near the driver side under the hood. However,
since we heard the Fuel pump prime they're likely OK. There's three of them just laying there.

-Disconnected plug: Look around for a loose plugable connections

-Fuel Pump may not be producing adequate pressure to start: He said the
Schrader Valve for checking pressure is in the back near the distributor
cap area. It will be on the silver fuel rails running on both sides of the top
of the engine. He's going to let me borrow his Fuel Pressure Meter to
check the pressure. HE said as soon as you hit the Ignition Switch to on
(KOEO), the pressure should jump to 40 to 45 PSI on the meter. IF not we
have a bad fuel pump.


-Ignition Module may be bad as it is interconnected with the ECM (Engine
Computer Module) Many times, if bad it simply will not start even with
Starting Fluid. However, that is not always the case since a bad Ignition
Module may interfere with the Fuel Injectors and firing order. He
thinks we should change it regardless. It's located under the distributor
cap. When we remove it make sure we don't drop the screws into the
distributor. Autozone or Advance can check it for us for free. HE warned
not to get one at Advance as they are many times bad off the shelf.

-I mentioned the Coolant Temperature Sensor and he agreed that it could
also be a problem as it effectively tells the ECM either to decrease (lean
out) or increase fuel delivery to the engine among other things.

-Also I was thinking, If the the ECM is detecting the Gas Pedal in a fully
down position the fuel Injectors won't turn on. It needs to be checked out
as well.

-Also, we'll run the codes to see what's else may be set besides EGR code
32.

Any other Ideas as I going up Saturday to try and fix it?

CBR1000RR

iTrader: (1)

Sounds like you have it covered. If it will start with starting fluid then the ignition system should be working correctly. First thing I would check would be fuel pressure. If that checks out ok I would use a noid light to check for injector pulse. That covers most the things you need for the engine to get fuel.

Shinobi'sZ

I have had some similar hard start issues that come and go...my guess is that it is the throttle position sensor, coolant temp. sensor, or intermittent faulty injector. In my case it is difficult to troubleshoot as the problem is not consistent...so I will drive until breaks.

Your case appears to be much simpler...it doesn't run unless you are getting fuel. So you should test your fuel pressure as suggested. Does it stay running once it is started or merely start to run until it burns off the starting fluid????

Also did you replace the fuel filter?

If you only had one bad injector the engine would still fire and only run on the cylinders that are getting fuel.

The thing is it fires and runs when you give it fuel..so agree no problem with ignition....so check the parts responsible for fuel delivery.

CBR1000RR

iTrader: (1)

Keep in mind that TPI is a batch fire system so each bank of 4 injectors are all on the same circuit. If one injector is shorted it will take out that whole bank.

topfile

Keep it coming Guys.....

I need all the help I can get. I'll be working on it in the Student PArking garage tomorrow, so I'll need to bring everything I
can think of.....


CBR1000RR- Noid light is great idea! I'll about purchasing one somewhere.
Thanks for the heads up on the injector operation.


Shinobi'sZ- You Said ..

Does it stay running once it is started or merely start to run until it burns off the starting fluid????

No, it dies after burning starting fluid off in less the 3 seconds.

did you replace the fuel filter?

No I didn't, it looked brand new ,clean and shiny , so I assumed it was OK.
Mechanic thinks it was recently replaced as well as he likley did the work.


my guess is that it is the throttle position sensor, coolant temp. sensor,
or intermittent faulty injector

Well you could be correct I'm taking the 2 wire Coolant Sensor with me.

as to the Throttle Position Sensor... Where is it?

Please more comments.....

mnorton

The TPS is on the throttle body, connects directly to the butterfly shaft, passenger side.

I'd bet it's a fuel pressure problem. Should be about 40 psi with key ON. Watch it leakdown with key OFF, should hold some pressure for a while, but will likely leakdown, that's typical. Needs about 32 psi just to start. These cars are famous for failing fuel pumps. They are difficult to replace as it is installed inside the fuel tank. $100 part, $500 labor...

CBR1000RR

iTrader: (1)

Like mnorton said it is probably a fuel pressure problem. If it is, it's probably caused by a bad fuel pump. Thats something you will not be able to replace in the student parking garage unless your really determined. Some of the tools I would take would be:

DVOM(digital volt ohm meter)
test light
noid light set
fuel pressure gauge
Spark tester(should need, but just in case)
Piece of wire to be used as a jumper
and basic hand tools

With that you should be able to figure out whats wrong with it. Also if you can get your hands on a OBD1 scan tool that might make things easier. Then you could just look at the ECM data to see if any of the sensors are reading incorrectly and check for any trouble codes. You can also read codes by jumping the A and B terminals on the diagnostic connector by the fuse block under the dash and counting the flashes of the check engine light. Let me know if you need more information about that.

Do you have a repair manual for the car?

topfile

Will be doing the ECM A and B jumper thing tommorrow, as That's how I got code 32
EGR valve.

Here's what I've Got so far for the trip.

Tools;

-New Noid and IAC Light Set includes GM TBI, GM PFI, GM SCPI, and GM MULTEC2
Item #W89501 from Advance $21.89
- Snap-On Fuel Injection Presure Gauge Set #MT337B, Loaned from my Mechanic
- 5.5mm socket for the small bolts on the Ignition Module From Mechanic
- DVOM(digital volt ohm meter)
- Jumper Wire
- Jumper Cables
- Every tool I can Think of that will help
- PB Blaster Penetratiing Oil just in case.
- Haynes Repair Manual

Parts;

- Ignition Module made by Standard #LX-340
- Engine Coolant Temperature Sensor by Standard #TX3
- Throttle Position Sensor by Standard # TH42


Don't have the Spark PLug Checker. Talked to my Mechanic and He agrees getting
the Fuel Pump out will be Very Tough as He just Did a RS Camaro.

Remember, the Fuel Pump sounds normal so I'm hopeful. The Mechanic Said " That
Ignition Module is likely your problem right there". He showed me one he just
removed
and advised me to be careful when installing it as the Distributor Cap groove seals
over top of it and I need to be careful not to force it or I'll ruin the Module.


I told him that Autozone could test the one I removed and he just laughed. "No Way"
he said "That can't completely test it."

What am I forgetting?

Mnorton- Thanks for the Tip on the TPS location, hope it's not the Fuel Pump.

CBR1000RR

iTrader: (1)

I think you should be able to get it figured out with what you have. Since you said the fuel pump sounds normal the fuel pump circuit should be ok. Sometimes the rubber hose on the pump in the tank rots and starts to leak. When that happens the fuel pump runs normally but all the pressure bleeds off in the tank.

C-Titan

iTrader: (2)

i had this same exact issue in my 91 with its old 305 around the same mileage... we replaced literally everything under the sun and it still wouldn't work (only starting temporarily with s\f)... we decided to do a compression check, what we found was 3 cylinders just above nothing... needless to say wasn't to thrilled... before investing anymore money i suggest checking the compression... even if you find its ok, you'll have a piece of mind knowing that there is a solid engine in the car...

CBR1000RR

iTrader: (1)

True that low compression can cause a hard or no start. I would check the easy stuff, like fuel pressure, first and check compression as a last resort. Pulling all 8 spark plugs in a parking garage and checking compression is going to take a good amount of time.

topfile

do a compression check

C-Titan - Well I hope That's not it. My daughter said the car was running strong.
up until last night. Parked it and 5 hours later.....no start. Very abrupt. I will say that it tended to be slightly harder to start when warmed up, but only intermitently.
Cold start: seldom if ever a problem.

Also, when we puled the plugs they all looked very nice just as one would hope.

I'll likely proceed as follows;
-Visual inspection of all connection
-Identify and inspect fuses
-Check Fuel Pressure 35 to45PSI expected
-If pressure OK I'll do a NOID test
-IF that's OK I'll replace the CTS
-IF that's not it I'll pull the Ignition Module and replace.

Anyone think the VATS (Vehicle Theft System?) is to blame?

topfile

You guys please post anymore ideas.

In the mean time I'll likely have some feedback from the Students Garage around
12 noon EST Saturday (tomorrow). Please Check back as I'll try to post finding and
possible clues.

Thanks and Keep it coming!

Shinobi'sZ

I want to say that I have had a situation with another vehicle where I could hear the fuel pump prime..but the FP was still not making enough pressure to let the car run.
Being that your car will run on started fluid but then die after it burns off...leads me to believe that it is definetly fuel (delivery) related. You may have to be prepared to replace the FP. There is way to do it from the trunk...but it involves cutting the top of the truck pan...and the FP is sitting right there...pretty easy. Otherwise you have to drain and drop to get to the pump. I concur with others who said to check the Fuel Pressure at the rail first...I will keep my fingers crossed for you.

shdtree

A buddy told me to pull back the carpet above the tank to look for an access hole and sure enough the previous owner had cut through the body just above the fuel pump probably to service it once before.

It's risky (relieve pressure, drain tank, well ventilated area, etc. etc.) but you have about 1/3-1/2 of an inch clearance so don't cut too deep or your into the fuel lines and then into the fuel tank.

The center of the pump is about 10" from the rear seatback, so you could cut about a 9" or 10" wide rectangle from the seatback (i.e cut along the grooves in the sheet metal) toward the rear of the trunk area at least 14" long. The fuel lines run between those grooves, under the metal from the seatback to the trunk.

Peel the sheet metal back so that you can bend it back afterwards and there it is. If you do it with a stone cutting wheel, then it should take about 30-45 minutes.

If you accidentally cut through the steel fuel lines, then have some rubber lines and clamps standing by to retrofit.

topfile

Shinobi'sZ-


Thanks for crossing your fingers it worked. The Fuel Pressure reads 44PSI at cranking
and settles to a solid 41PSI. Fuel PUmp OK.....Whew!

Sorry about no UPDATES till now the Student Garage had no WIFI.

The NOID lights came in handy they told me that the FUEL INJECTORS
were not being pulsed at all, neither side of the Engine. Fuel Delivery
Problem. Although they had a solid fused 12V source just were not being
ground pulsed by the ECM.

I decided to replace the Igniton Module as it was original GM. NO luck.

It was actually the PICK-UP COIL ! Instead of reading 600 to 1500 ohms
it was reading OPEN. A new one reads 850 ohm. This coil is in the Distributor
connnecting to the back of the Ignition module.

Unfortunately I've not been able to replace it yet.

I noticed a couple of things:

1. Previously the Tach has been pegging right away to right. Now it's actually
trying to react to the cranking as it read 1000 to 3000 rpms, albeit wrong it's
reacting before it nearly pegs once the key is released to the Key on position.
I know that parts of the Ignition Module/ Distibutor circuit actually connects
to the TACH through the Ignition Coil.


2. The SECURITY light on the the dash was activated SOLID when I cranked it. and
the CODES returned code 46 which is VATS (vehicle anti-theft system?). The
Security light came on anytime I tried to start and ran with Starting Fluid.

VATS would only clear if I unplugged the ECM power connector near the passenger
strut mounting. Susequent cranking without starting Fluid would not activate the
security light. Explanation?


Now I got to get the Distributor OUT to replace the PICK-UP COIL.

The Bolt somewhat beneath the Distributor is hard to access. Any ADVICE?
I have a 9/16 th distributor wrench from my Olds 307 that should fit. It's
just really a tight area with the NUT hiding a bit under the distributor.

ANY THOUGHTS?? suggested tool?

They I need to disassemble the Distributor at the Student Garage site to get the
pick up coil in. ANY TIPS???


Thanks All....

topfile

Well the PICK-UP coil wasn't preventing it from starting after all.


It's still dead at the Student Garage.

Recap;

Runs momentarily with Starter Fluid then quickly dies

-5.0 Z28 1991 TPI
-ECM is not Pulsing the Fuel Injectors
-All under dash fuses look or test good
-Fuel Pressure at 20PSI at KOEO and Goes to 44PSI once Cranking Begins, settles firmly at 41PSI
-TACH reacts to cranking
-CODE 46 set (VATS)
-Ignition Module and Pick-UP coil replaced.
-SECURITY comes on Solid after first crank attemp.
-A month ago had duplicate ignition key made (has the chip)
-Both old and new key produces same result.
-Had intermittantly been slighty hard to start when warm
-Runs 220F in stop and go summer traffic
-EGR code sets after long trips during cruising speed
-a little more than a Week ago had new valve stem seals and spark plugs installed
-Previous owner let it set for months


Thursday
-After setting for 5 hours it would not start. Cranks fine, fuel pump sounds fine, ....just no start.

The only thing not addressed is the SECURITY LIGHT on the cluster.

Questions:

1. Will VATS (Vehicle Anti-Theft System) prevent the fuel injectors from turning on but allow cranking?

2. Normally does the SECURITY LIGHT come on solid during cranking? Daughter doesn't remember seeing it before.

3. What Sensors could prevent the ECM from turning on the Fuel Injectors?

4. Any recommended testing plan? I have a Multi-Meter and know how to use it.


What do ya think?

CBR1000RR

iTrader: (1)

The security indicator should go off after about 2 seconds. If the light stays on then there is a problem with the pass key system. A common problem with the system is the wires that go to the ignition lock cylinder break. What I've done before to temporarily fix this problem is measure the resistance in the resistor pellet on the key, go buy a resistor with the same resistance(if you can find one), and splice it into the two small wires at the base of the steering column.Also to check to see if this is your problem disconnect the 2 pin connector at the base of the steering column and with the key inserted in the ignition, measure the resistance between the two terminals while turning the key from off to run to start. If the circuit is open at any time while doing this then thats your problem.

transam85dudeman

hey i was talking to this guy who got his car runnng. he did everything you said. it turnd out to be a bad oil pressure sensor. the sensor gives the ok to let the engine run. try seeing if you can chase the wires. and test the ohm on the coil for the hell of it. heres his link... https://www.thirdgen.org/forums/tech...s-out-god.html

THE87IROCZ

I'm having the same problem with my 91 firebird. Will run on starting fluid but injectors won't pulse. But I do know that the VATS module does need to send a 5 volt reference to the ECM that tells the injectors to fire (among other sensor inputs).

This link helped me out which is part of this site. Maybe it will help you

https://www.thirdgen.org/vats_passkey_system

THE87IROCZ

alldatapro.com states code 53 is a VATS DTC but doesn't say what code 46 is but my Haynes manual says 46 is a VATS code. Mine has a code 53 so I don't know which one is right.

topfile

As I understand it the VATS Module does three things once key chip resistor is detected correctly;

1. Activates the Starter Enable Relay
2. Activates the Dash solid SECURITY light for 2 to 3 seconds once Ignition switch moves to the Key-On Engine-Off position.
3. Signal sent to the ECM to tell it to fire the Fuel Injectors

If the key resistance if read incorrectly just once during start attemp, one must wait 4 minutes before a succesful starting attemp can be made.


Now for what I have and what can be deduced;

-I have new key and an old key.
-First trying the New key to start produces no Security Light at all.
-Second trying the OLD key ( KOEO )Activates the SECURITY which doesn't turn off until the key is removed.
-Third Trying the New KEY again now produces the same result as the second try.
-At all times the Starter will crank as normal.

Deductions?

Another good site:
http://www.vatssucks.com/

THE87IROCZ

I have found that even if the engine cranks (which I got to by bypassing the relay) that the VATS module may not be sending the right signal. That signal I have not yet figure out. I know its supposed to send a 5 volt reference to the ECM but I don't know for how long or if the ECM needs to see anything else. I have read that if you get the car started and running that you can unplug the VATS module and the vehicle should still stay running. But as for what signals the ECM needs from the VATS module to allow the injectors to pulse at start up I have not yet found. If I do find something Ill be sure to post it.

As for replacing the module I have found they are supposedly only sold through the dealership and cost about 300 and have to be programmed by them even though the programming process only consists of installing the module and turning the key on. But that it is very rare for the module to go bad and it is usually a problem with the two wires going to the ignition.

topfile

My best guess and test plan

1. KOEO: Determine if 30hz 5V square wave signal is going to ECM, not sure how to
do this yet. Ideas?

If it is then maybe my ECM is bad or other wiring issues.

If no signal move to step 2.


2 . If no signal troubleshoot VATS Module by making sure its seeing the correct
resistor value of the KEY.

Identify connector that supplies key value on VAT MODULE. Unplug it.

Using ohm meter at 20k range read pre-determined key value at KOEO position
on Ignition.

If it's seeing the key value then Verify power to VATS Module. If power is present Bypass using online kit from Painless Wiring #64023 or replace module.

If the Ignition lock cylinder isn't providing the Key Resistor value correctly
move to step 3.


3. Construct using 1/4W resistor value from Radio Shack a substitution resistor value for the KEy within 5 %? . Connect this Value to the VATS MODULE connector.

This is the least expensive approach but will not likely solve the problem
as the Starter Cranks. Normally if the KEy isn't reading no crank occurs.
Unless previous owner has bypassed the Starter Enable Relay.

THE87IROCZ

After finally finding where the VATS module was, which resulted in puling the dash and finding it on the back of the dash next to the firewall I tested to see if I could get the resistance reading of the key while it was in the ignition. I found no reading so I pulled the ignition out and found 1 wire broke. Autozone carries ignition for 25 bucks and dealership will cut key to match or 25. We will see if that finally fixes it. I guess VATS module will send 5 volt reference to ECM even if it doesn't detect the right resistance

topfile

Going up Friday (360mi Roundtrip) to try my test plan.

Betting it's VAT and all I'll need to do is substitute the Resistor Value for the Key.

The Reason I think this is the way the Security Light Responds.

First start attemp sets no security light on the dash no matter what key I use.

The reason I believe this occurs is the VATS is not seeing the resistance and doesn't know there's a key in the ignition until I crank the engine. After that point any time KOEO is activated the security light sets solid and stays on until the key is removed.


THE87OROCZ- Are you starting?
Did your's act like mine above?

Anybody else?

topfile

CBR1000RR- Am I on the right track?

Anyone Else?

CBR1000RR

iTrader: (1)

Yeah, your on the right track. I think you'll get it figured out this time.

THE87IROCZ

It does sound like a VATS issue. Did you make sure that the wires to the ignition were ok and not broke. After checking every reference value at the ECM and verified all the wires ok I finally went after the VATS module. When I went to check to see if the key was being read at the module I found there was no resitance found. So I pulled the ignition out and found the wires were broke. I put a new igntion in and got a duplicate key cut with the resistor chip in it (from the dealership) and the car started right up. Only thing that I see different from mine and yours is that my car doesnt have a security like. I just got code 53 which I found out is another VATS code.

mnorton

As a last resort, you could go the route of getting a PROM Emulator and turning off the VATS flag to disable VATS all together.... just a thought. I realize that's a pretty wild tangent, but I think it would eliminate the VATS question.

topfile

VATS! Fixed!

It was the portion of the VATS that measure the Key's imbedded resistor chip. As
with many others here, one of the two wires running up into the steering column was open.

Therefore the key could not be read. Therefore the ECM would not allow the car to start.

Previously my first start attempt set no Security light on the dash no matter what
key I used. I believe because VATS didn't know a key was in the ignition due to the
broken wire mentioned above. Once I bypassed the key measuring circuit of VATS
the Security Light turned on with my first attempt to start. The light didn't go off
as I expected in the KOEO position even after waiting 10 plus seconds. However, the
Security light did go off once I moved to the Cranking position and it STARTED!

My key chip measures 3.00K ohms using my VOM meter. I simply choose two resistors
valued at 1.5K ohms and connected them in series to give me a value of 3.00K. Then,
after finding and unplugging the two wire connector (which employs two small thin
white jacketed wires incased in a bright ORANGE outer jacket) above the drivers feet.
I plugged in the two series resistors in the back of the two pin male connector, running towards the VATS module away from the column, for a quick test.

Once I determined this was the Fix, I made it more permanent by clipping the small
white wires going up towards the Steering Column. The female side of the connector
then dropped to the floorboard. Then I soldered my 3.00K ohm resistor network into
the two remaining wires of the female connector and covered it with black silicon.

Once dried, I plugged this new more durable network back into the Male connector
end. This 3.00K resistor network became a substitute for the Key chip resistor. Thus my VATS sees a key at all times.

As I suspected, my Starter Enable Relay was inadvertently bypassed by a previous
effort of a earlier owner. So my Starter would crank but the Fuel Injectors would not
activate.

It's all good now!

Thanks all!!! My Daughter is very happy to have her prized Z28 back.

mnorton

Good job! You ARE the man!

THE87IROCZ

Sweet. Guess that is something we both will have to check first in the future if this problem ever occurs again.