P0303 - 1996 Lumina need help

All,

I'm running out of idea's. It all started with a cam sensor code, intake manifold leak (non-internal) and a #3 misfire. I am now trying to fix the #3 misfire. So far I have replaced the wires and plugs and swapped the coils. Next I was going to check for spark and swap fuel injectors.

Am I missing anything else? I thought of using a 3M injector cleaner (rec. by mechanic) but I am fearing it will kill the O2 sensor and catalytic.

Please help

Thanks, mazzov

1996 3.1 lumina 115k

You're on the right track. If you swap the injectors and the misfire moves with them, you found your problem (bad injector). If it stays on cylinder 3, check the injector harness with a noid light to be sure that injector is getting a signal from the ECM. You shouldn't have any issues with any cleaner harming the o2 or the cat, as long as you follow the instructions.

O.K. I am almost on empty and there is still no change after adding fuel injection cleaner. :banghead: Can I use the test probe and poke the fuel injection wire to check for a signal or do i definitly need to swap them?
When I first start the car in the morning it will give me a blinking service light. Once I start moving the light will stay on constant. If I am on the highway and I am going up a hill the light will start blinking again and then go back to being constant again. I know that a blinking light indicates a misfire and a constant light indicates an emissions problem (according to the manual). Now when I hook up the scanner it will give me the P0303 (misfire #3) code. after clearing the code it will reappear within a mile or so. Is there a chance that one of the O2 sensors went bad & how can I test it. The car use to get 27mpg 2 months ago I am now at 21mpg.

Any feedback will be appreciated. Inpection is due this month :frown:

no its a misfre code. check all the conditions that would cause a misfire on cylinder 3. And no you cannot use a test light on fuel injectors, you will fry the compluter. You have to use a noid light, or i've seen LED test lights that would also probably work. You can also unplug them all and do an ohm check. If any are out of spec with the rest you found the problem. Have you ruled out anything major mechanical? Done a compression test yet?

tblake,

Thanks for the feedback. I have not done a compression test (seems like a pain). When I changed the plugs I did notice that the #3 plug looked a little wet but not oily. I will go back to verify and try to post a pick. As far as a noid light I have never heard of them (it's been a while since I've worked on cars). How would I use the ohm meter? Where would I hook it up to? Is it easier to just remove the plenium and swap the injectors?

Any feedback will be appreciated.

yeah, its probably easier to remove the plenum and swapping them around would totally deny or confirm an issue. You would measue resistance across the terminals of the fuel injector itself and do this to all 6, if any are out of spec with the rest you may have found the issue. However this does not rule them out. Just do a compression test, keep the plugs in order, and see what the plug #3 looks like. No sence trying to narrow down a misfire if in fact the cylinder doesnt hold compression (which can cause a misfire also)

noid lights are just LED's in plastic cases that plug right onto the fuel injector harness and bling at high speeds so you can tell the fuel injector is getting current needed to operate.

ditto what tblake said in his last two posts in this thread.

Thanks guys. I will let you know the outcome.

When taking off the plenum is there anything I have to watch out for? Are the fuel injectors under any kind of pressure? Water connections?

I wound up picking up two injectors. I figured that if I'm gonna have it apart I'm just going to change it.

Thanks, Vince

Before disassembly, pull the fuel pump fuse and attempt to start the car to relieve the fuel pressure. There are two small coolant lines that go to the throttle body attached to the coolant transfer tube that runs along the front of the engine from the water pump area, over to the drivers side, under the throttle body and to the heater core.

I got some pics. How do I attach them?

Richtazz,
I took a couple of pics. If this doesn't work I will email you.
Can you show me the coolant lines that you had mentioned from these pics?

http://groups.msn.com/R-O-A-R-/shoebox.msnw?Page=2

http://groups.msn.com/R-O-A-R-/shoebox.msnw?Page=2 Last 5 pics

Starting near the water pump, where the coolant bleed valve is, follow that black tube that runs along the front of the engine, under the drivers side torque strut and then it turns 90 degrees under the T-Body. There are two small hoses that run from that tube assembly to the botton of the t-body. You will have to remove the air filter snorkel tube to see them.

http://groups.msn.com/R-O-A-R-/shoebox.msnw?action=ShowPhoto&PhotoID=19

From this pic, if you remove the rubber tube attaching the air filter housing to the t-body, you'll see the two hoses that run from the black metal pipe mentioned above to the bottom of the throttle body

O.k. here is where I'm at.

I removed the fuel injector and replaced with a new one. Now I am getting a p0303 code (multiple misfire) I am thinking that this could be due to the fuel pressure (I relieved the pressure thru the end of the tube). I am also assuming that this will clear up after driving around for a little bit.

After getting the fuel pressure up. Do I have to erase the code detach the battery let it sit overnight and then re-hookup the battery to properly reset the codes?

Is there any other possibilities?

Thanks, Vince

If you cleared the stored DTC after replacing the injector, and the code repeated, the problem was not likely the injector. If you never cleared the original error code, it will still exist and illuminate the MIL.

I cleared the codes prior to starting and when I finished I started it up and that's when the code appeared. After letting it run a little while I shut it off and cleared the codes. I took it out for a ride about 7 miles and the codes didn't reappear. I think that there may have not been enough pressure in the fuel line when I first restarted it and that's why it tripped the code.

I will probably schedule my inspection ASAP after a longer ride.

Vince

O.k ready for this.

Im in line to go to inspection. The guy takes the car and does his stuff. At the end he tells me that my "service engine" light is on. I said " that's funny it wasn't on when I brought it in". So now it is showing a p0304 (misfire #4). Seems like I'm back to step 1.

So after I left I reset the light and erase the code (it has not come back yet). Now I noticed that if I'm in neutral and I rev the engine it cuts out a little revs again and cuts out again. Has anybody had this happen.

Thanks, Vince

O.k ready for this.

Im in line to go to inspection. The guy takes the car and does his stuff. At the end he tells me that my "service engine" light is on. I said " that's funny it wasn't on when I brought it in". So now it is showing a p0304 (misfire #4). Seems like I'm back to step 1.

So after I left I reset the light and erase the code (it has not come back yet). Now I noticed that if I'm in neutral and I rev the engine it cuts out a little revs again and cuts out again. Has anybody had this happen.

Thanks, Vince
Unrelated to the misfire code, if you rev above 4k in neutral the pcm cuts the fuel to save the engine.

It's funny you would mention that because during thier test they reved the Sh%t out of the engine and that may have set off the light.

Yesterday about 10 miles after the inspection the light came on when the engine was reved when trying to get on the highway. I cleared it out this morning and it's been good since.

I'm stuck..:banghead:
Vince

Actually, I'm not certain the fuel cutoff RPM is programmed that low. I'll have to check the programming to verify that. Usually, the RPM fuel cutoff is set at something ridiculously high, like 8,000+ RPM. The Big Wedge could be right, since I haven't hacked any 191 V-6 programs (yet).

Another possibility is that the revs under no load created a necessarily very lean/hot condition, and that may have resulted in the detected misfire.

It's also possible that the ICM cannot fire the coil primaries at that high a frequency for any of numerous reasons, and that the lack of adequate spark energy at that RPM set the misfire DTC.

A similar situation could exist with a weakening CKP (crankshaft position sensor) that is not accurate with the higher RPM and does not switch reliably on every reluctor tooth. Even buildup or contamination on either the CKP face or the reluctor could affect that. The CKP input is what the PCM uses (over a time base) to detect misfire in the first place.

I had spoke to a local mechanic (the one that had done the intake manifold gasket). He said that it could be a vacuum leak throu the #4 injector o-rings. This could be checked with a spritz of starter fluid. If the engine revs there is a vacuun leak. So I picked up orings for ALL the injectors (apparently this is something I should have done the first time):banghead: . I also had mentioned the cutout to him a he said that it is normal so the engine doesn't blow up. He didn't understand why they would rev up the engine when doing an OBD2 scan. He said that he doesn't do that.:nono: I told him that if it fails again I would just make an appointment with him.:grinyes:

Does anybody put a little bit of grease on the oring prior to putting them into the manifold?

Thanks for the help.

Vince

Clean engine oil should be applied to the 'O' rings before installing the injectors. Make sure you get 'O' rings designed for fuel injectors. Most standard rings are Buna-N (nitrile) rubber, which may not permanently resist fuels and additives, and can eventually deteriorate. Viton is usually the material of choice for factory rings.

Use clean engine oil to lubricate the o-rings prior to installation.

Thanks for the oil idea. I got the o-rings from carquest so they "should" be o.k.

Vince

On the RPM cutoff issue, the factory programming cuts off at 4k (+ or - 500RPM) in park or neutral only, to keep overzealous free-revver's from blowing their engines. Normally while in gear, the cut-off is somewhere around 200-300 rpm over the tachometer's (if equipped) red line RPM (usually 5800-6200 RPM for most engines in GM W-bodies).