93 t/a in trouble

[Trans Am]

hi
i have changed the fuel pump, spark plugs and the oil, but the enginre turns and just doesnt start

i checked for pulse at the injectors with a test light and spark at a 3 plugs and its ok

how long until the fuel pressure drops ? i have fuel pressure, but it doesnt hold. will the car start with a faulty injector? it was leaking very bad and i blocked the fuel to it with some plastic. when i pressurize the system, of the injectors leak.

i think that it should at least start even with a bad injector

so, i have spark, pulse to the injectors , new spark plugs, new fuel pump the starter is ok, battery ok, engine turns but wont start

i m all out of ideeas, please help

[Craig 94 TA GT]

What about the regulator? It is possible that you will see pressure but will drop off quickly if the regulator is bad....it would simply dump the fuel back in the return line...or in the vacuum line if the diaphram is ruptured..

The fuel pressure should hold over a few to several hours. If you see a drop to 0 within seconds or even minutes, there is something majorly wrong. If it drops from say 40 to 20 in 2 hours, it isn't too bad, but the system is capable of holding better pressure.

[Joe 1320]

There is info contained in these two threads......

http://www.f-body.com/forum/showthre...&threadid=4562

and


http://www.f-body.com/forum/showthre...ight=Optispark

[Trans Am]

*update*

hi
thanks for the tips


i am going out of my mind!!!!!
i have checked foor everything and the car wont start


today i checked the fuel pressure with a gauge: ~43.5 psi with keey on, engine of coourse off and then it drops to ~36-39 and stays there. its ok isnt it? when i crank the engine the gauge jumps around a bit ant then stays at ~43 psi. with the return line shut of, pressure goes to ~58 psi
injectors dont leak when system is pressurized
i lifted the fuel rail and the injectors work fine while cranking the engine
i took out 4 spark plugs and they were dry (they are new). where does the fuel go?
checked injector pulse for all injectors: ok, injectors spray fuel while cranking


all i can think of is this:
1. timing chain (but i can see the valves moving through the oil fill hole while cranking). is it possible that the timing isn good and the engine turn over fine? and the injectors spray fuel on a closed or partially closed intake valve?
2. someone has mixed up the connectors to the injectors? how can i find out on a 93 wich connector goes where?
3. i am just stupid and cant find out what the problem is

i ll go crazy, i m working on this car since july last year. it just stopped while i was at a stop light. no funny noise, no ses

[Craig 94 TA GT]

I'm running out of ideas too. Although you see fuel out the injectors, to really eliminate the fuel system would be to get a new regulator. I don't know if you'd be willing to spend the money to get a new one in order to diagnose the problem, but IMHO, it might be worth it. When I saw the fuel pressure drop from 40 to 0 psi in 2 seconds, the T/A would run a bit rough. However, after a few more start-ups, it wouldn't catch anymore...just keep cranking, like what you're experiencing. It doesn't make sense either because the fuel pressure was the exact same thing before and after...yet it just wouldn't start anymore. Also, when it was cranking, I saw a steady 43 psi of pressure in the system, so it did have pressure....but didn't catch. That's why I can only suggest you replace the part ...instead of testing and tearing out your brain thinking of everything. On my T/A, once the injectors and regulator were replaced, the it had new life (i.e. she breaks loose on the downshift to 1st lol). I guess it might be worth the replacement, but if it isn't the problem, you just lost the money of the cost of a new one. Good luck.

[Joe 1320]

Originally posted by Joe 1320
Step 1. Connect a spark plug tester to a spark plug wire and
check for spark while an assistant is cranking the engine.
Check each plug independantly. this checks for open
spark plug wires. Spark in one or more than one wire
indicates the problem is in spark plug wires or optispark.
If no spark exists, go to step 2.

Step 2. Check for spark at the coil wire with the spark tester
while cranking the engine. A spark indicates the problem
is in the distributer (optispark). If no spark go to step 3.

Step3. Perform check on ignition coil.
a: Unplug coil electrical connector and check pink wire for
12v. If power go to b.
b. using ohmeter low scale, hook up the leads to the
primary terminals on the ignition coil. Should indicate
very low resistance. If not, replace coil.
c. Using the high scale, hook up one lead to the primary
terminal, the other to the secondary terminal. Should
not read infinite resistance. If it does, replace coil.

Step 4. Disconnect the ignition module connector and with the
key on, check voltage at terminals A and D on the harness
side of the connector. (pink/black and white/black wires)
If under 10 volts check for faulty circuit from the ignition
module to the coil or check for grounded external coil
circuit. If 10 volts or more, change the voltmeter to a/c
scale and measure voltage on terminal B while engine is
cranking. (white wire). If 0 volts, Have ECM checked. If 1-
4 volts, with the key off, disconnect the module
connector. Install a LED type test light on the positive
battery terminal and probe terminal C on the harness side
of the connector (black wire). The light should illuminate.
If not, check ground wire in the harness to the module. If
the test light is on, go to step 5.

Step 5. Remove the coil wire from the coil and ground it to the
frame. Connect LED test light into the optispark harness
connector red wire terminal C. The harness connector that
you will use is located on the passenger side of the
engine up near the fuel rail. You will need to insert a back
probe pin into terminal C. If the test light flashes when an
assistant cranks the engine, the optispark is suspect. If
no flashes, replace the ignition module.

If the above tests results are correct and there is still no
start, it is tough to to tell the difference between a
faulty module or optispark. Module = Cheap$$, optispark
=moderate $$$.

how about these diagnostics? specifically:

Step 4. Disconnect the ignition module connector and with the
key on, check voltage at terminals A and D on the harness
side of the connector. (pink/black and white/black wires)
If under 10 volts check for faulty circuit from the ignition
module to the coil or check for grounded external coil
circuit. If 10 volts or more, change the voltmeter to a/c
scale and measure voltage on terminal B while engine is
cranking. (white wire). If 0 volts, Have ECM checked.

[Trans Am]

Craig , im glad your car is running ok now. i ll do what you said, but i ll have to wait until i get the fpr and the injectors. Kevin is helping me out with this. what a nice guy


Joe 1320, i checked for spar with a spark plug, i dont have a spark plug tester. i ll do this at all spark plugs as soon as i can. is it ok with a spark plug? also i want too see if the spark is at approximately the same time as tthe same cylinder injector pulse. it should be almost simultaneously ,no?
i ve ruled out the distributor, cause spark goes to the plugs i checked so far- is that ok?
the wires to the coil are checked ok, only the coils resistance is ~10.000 instead of ~7.000 ohms accordin to the repair manual. i am thinking that its ok
step 4 ok.

i really need help on this one



thanks

[N20LT4Bird]

I may be stating the obvious, and if I am, feel free to flame.....but have you done a compression test? Testing compression in each cylinder will give you valuable information.

And if you have compression, spark, and fuel, I would look into a possible ECM or ignition module problem becasue these crucial elements are not being timed correctly.

[Trans Am]

i will do a cmpression test as soon as i get a gauge
is there any other way to find out if cylinders dont do enough compression?

[N20LT4Bird]

You could do a leak down test on each cylinder, but its more of a PITA and you still have to by the tester......so, no - just get a compression tester - its a good tool to have anyways.

[Trans Am]

if the engine just died while at idle and then started again, is it possible that i have compression problems?
what happens if 1 cylinder has low compression?

[Joe 1320]

Originally posted by N20LT4Bird
I may be stating the obvious, and if I am, feel free to flame.....but have you done a compression test? Testing compression in each cylinder will give you valuable information.

And if you have compression, spark, and fuel, I would look into a possible ECM or ignition module problem becasue these crucial elements are not being timed correctly.

A compression test is a good idea. If the timing chain were to have jumped a tooth, you would get a no start........ not sure if there would be interferance with the valves on an LT1, but have seen it on other motors where you seem to get spark and fuel and still a no start condition. I've also broken a crank clean in half where the starter would engage and spin the back half of the motor perfectly, leaving the front half motionless.

[N20LT4Bird]

I think the LT1 is a freewheeling engine, so smacking the valves is not an issue, but if the chain jumped - a compression test would tell you. If the valves arent opening and closing correctly, your not gonna have good compression and potentially a no start. It would seem odd that the chain would jump just sitting at a light though. But.....I have seen stranger things

[Trans Am]

Originally posted by Joe 1320
A compression test is a good idea. If the timing chain were to have jumped a tooth, you would get a no start........ not sure if there would be interferance with the valves on an LT1, but have seen it on other motors where you seem to get spark and fuel and still a no start condition. I've also broken a crank clean in half where the starter would engage and spin the back half of the motor perfectly, leaving the front half motionless.

i think the crank is ok cause the front balancer is turning

the chain jumping a tooth, wont make some noise?
at the throttle body the engine draws a lot of air while cranking. i ve noticed that by accident as there was a plastic bag i forgot to take off blocking the throttle body intake, so i guess the intake valves are ok

[Trans Am]

Originally posted by N20LT4Bird
I think the LT1 is a freewheeling engine, so smacking the valves is not an issue, but if the chain jumped - a compression test would tell you. If the valves arent opening and closing correctly, your not gonna have good compression and potentially a no start. It would seem odd that the chain would jump just sitting at a light though. But.....I have seen stranger things

is there any other way to check that?

after it stopped, it started again after a lot of tryes