Hey folks.

Went out to start the '99 T/A today and got a very bad misfire at startup; it barely caught on and ran. Within seconds, the SES came on. I scanned the car and got po200 but no others.

In a rush for work, I didn't have time to check anything other than fuel injector connections to the injectors from the harness; everything seems fine.

I searched around on the threads here, looked online a bit from some of the provided links and I think I have an idea of what I need to do:

* verify injectors are getting a signal from the PCM. I'm planning to use noid lights. I understand if the light flashes the signal is good. Is that enough to verify the pulse signal?

*check to see if the injectors are working. How do I do that?

*recheck to see any wiring damage on the harness to the injectors. Check for wiring damage from the PCM.

*what I don't understand is why the po200 code doesn't tell me which cylinders are misfiring, or why i dont have any pending or stored misfire codes, or is it an overall system failure? Another thing: the problem is intermittent. While repeatedly trying to start the car it would be perfectly fine, and then during another restart it would be bad again.

What else do you guys recommend? I've read here that po200 almost always means a PCM issue but I'd like to check the smaller stuff first. Someone also told me that it could be fuel pressure related, but I don't think so. Another suggestion was also the front O2 sensors, but wouldn't that throw a code? Any suggestions will be greatly appreciated, thank you...

 

I'd be checking your fuel pressure at the rail first. That will tell you your pump is making it to 58 PSI and if it's holding 58 at key one and not an injector leaking down. If your pressure is ok and not leaking down after multiple checks, then I think it would be time to start looking for a pulse signal to the injectors and measuring the ohms on them to make sure they are able to fire, powers and grounds ect.

It's not impossible but unless you have rodent signs then wiring damage is not going to be very common unless you've been messing with them recently or have some other reason to suspect that. I'd suspect your pump is starting to go as much more likely with the age of our cars and it's moving parts as compared to wiring and you not being the in the rust belt. A bad fuel pump will work occasionally as you described but it will eventually get worse and strand you if you don't check it out soon.

As far as the scanner not telling you a cylinder, that could be whatever scanner and software you're using, I know my Amazon special doesn't read half the info the car can spit out where my Altec or HP Tuners can give me about everything. Maybe head to a shop or ask a buddy if they have a scanner to compare it to. Your O2s don't really make sense here as you are just cranking and in open loop until it reaches temp, until then it's using your cranking VE table to start and that didn't change.

 

Hey thanks for the response! As a precaution I checked the fuel pressure at the rail and it is reading 60 psi at key on, idle and key off.

What I've done so far is ohm the injectors, and they all passed at 12 ohms. I also checked for 12V at the injectors with the key on and they all came in at around 11.6. I was going to put a noid light on each injector to test the pulses, but, wouldn't you know it, the car ran perfectly after I plugged everything back in. Later I restarted the car and got the P0200 and misfire again, but still with no misfire codes.

I'm guessing that because the p0200/misfire is intermittent, I'm going to have to wait until the car starts misfiring again and start diagnosing from there. Do you think it would be a good idea to check continuity and resistance between the PCM and the injector connector wires? What I wouldn't give for a scanner that could count individual cylinder misfires; I'd have this solved in twenty minutes.

Thanks again for your response...

 

So going through the list:

Fuel - Pump checked out on the test (could still be this), injectors show good ohms (should mean they are capable of firing), I'm assuming you saw no bleed down on the pressure after reaching 58 PSI for a while, the noid lights could help find that but if you have a broken wire the act of moving wires and connectors could mask that issue

Air - I'm assuming the intake path is clear, you can unplug the MAF when it's happening and eliminate that entirely, only other thing would be your MAP, hopefully your scanner can output what it thinks the pressure is at when it's having issues

Spark - your Crank sensor could be acting up if it's not seeing the reluctor wheel like it wants to, best way to check it is with a scope but I'm not sure you have one of those, same goes for the cam sensor but the CPS is a more common. Alot of people wing new parts here since they aren't that expensive but if you do make sure you get a GM one or something that isn't chinese garbage or your going to cause more problems than you fix, other than that you can pull your plugs make sure they are still good and check your coil wiring just like the injectors for powers, ground, and pcm trigger

I'm also pretty sure that you have compression since that is a bit obvious. One thing you could do is when it happens shoot some brake cleaner in the intake without disturbing the wiring and see if it fires up, that will for sure tell you it's maybe not getting enough fuel and you can attack that or eliminate it from the list here. You could have gotten lucky as well here with the fuel pump if you just have a couple bad sections in the motor commutator and you've just gotten luck by it not stopping on them, sometimes you can check that if when it's not wanting to start thump the gas tank pretty good and see if it's cured, similar to a bad starter motor, the same thing happens to the pumps. Only way to for sure check that the pump is 100% is again with a scope though to look for a bad section where resistance gets high.

 

That should give you a good breakdown too of what to be looking for.

 

What does PCM code p0200 mean on injectors?

This means that the PCM had detected a malfunction in one of the injector circuits. In other words, the PCM commanded the injector on/off but did not see the subsequent change in electrical current.
It is very vague... Like you suggested try looking for a scanner that will show a recording of the live data when the code was set.
Most likely an injector going south or the injector circuit has poor integrity somewhere

 

Well **** I didn't look up this code. So ignore my book I wrote.


There's a similar problem and how to test with basic tools.