Tinkerer

HELP - I have a 2004 ASTRO van that is giving me fits. It runs rough at idle. I have changed the distributor cap, rotor, plugs and wires ( from GM ) NO CHANGE. I took it to a repair garage and they worked on it for two days.
They found that it was missing on 5 or 6 ( sometimes it is 5 and sometimes it is 6. If they turn off the injector on the one that is missing nothing happens. They did a smoke test of the vacuum lines and intake - no external leaks.
They changed the distributor, no change. They flow checked the injector and all of the flows were the same. They don't know what is wrong. When the engine is cold it is less noticeable. when the engine is hot it can stumble enough to stall sometimes.
Is it possible that the problem is caused by a lean condition due to a bad O2 sensor or could the crank position sensor go bad. They changed the distributor was changed because the gear was badly worn. ( they couldn't just change the gear.? )

Any ideas?????

donzi matt

iTrader: (1)

Check for a leaking fuel pressure regulator. It mounts under the intake plenum and when they leak they will provide an over rich condition on 5 and 6. After it has been sitting, disconnect the air snorkel from the throttle body, open the throttle plate and sniff for fuel. If you smell fuel, attach a fuel pressure gauge, turn the key on to prime the fuel pump, and see how fast it bleeds down. It should hold steady pressure after the pump shuts off. A competent shop should have been able to pick up on that when changing the injector, sounds like they are throwing darts at the problem. Does the misfire go away when revved up?

Tinkerer

The miss does seem to go away when reved up BUT it acts like it is not getting fuel. NOT flooded. If the injector for the cylinder that is missing is shut off there is NO change in idle. They didn't change the injector. They just checked flow.

donzi matt

iTrader: (1)

Well it sounds like the ignition basics have been covered. Assuming a flow test was done with a scan tool and fuel pressure gauge activating and comparing flow of injectors, you can rule out wiring to the injectors and the injector driver in the PCM. My next step would be a cranking compression test and running compression check. If that checks out, I would start looking closely at the injector. I recently had a 96 5.7 liter that would pass a flow test, but misfired just the same. After ruling out everything else I popped the plenum and replaced the injector and my issue was solved. The trouble with these injectors is getting them out of the intake without snapping the retaining tabs to actually try and look at the spray pattern. The fact it is missing on 5 and 6 leads me away from an O2, as they are on opposite banks and are controlled by different O2 sensors.

Tinkerer

I still think it is a lean condition because the engine runs and idles perfect when it is cold and the fuel enrichment is on. After the engine gets hot it starts to idle rough. The hotter the air temp gets outside it idles worse.

Black Baja

iTrader: (2)

It 1 of 2 things. Either the valves are sticking or it's the distributor. You need to put the scan tool on it and go into data stream and look at CMP retard if its not 0 +/- 1 it needs a distributor it will probably be around 10 or 14. Go to the auto parts and get a new one for $75. It has to be dropped in perfectly and use the scanner to confirm it was dropped in perfect. There is no turning the distributor to get it right. If the gear was worn on the old distributor and the shop u took it to didnt pick up on this immediately they don't know what they are doing. You need to take it to someone that knows what they are doing so you don't keep waiting money. There is a chance that the gear on the cam is worn to bad to throw off the CMP retard along with the distributor. Your motor isn't lean or bad flowing injectors or injector harness the PCM is fine. Chevy doesn't have those issues.

Tinkerer

The distributor to crank timing WAS off 7 degrees - The distributor has been changed. It is now 0*. Compression came out OK.

turbo rr

iTrader: (3)

Sounds to me like the coolant temperature sensor.

FIXX

iTrader: (2)

any excessive smoke out the tail pipe? any power steering fluid leakinh on the ecm? hydra boost leaking? whats the milage?

Black Baja

iTrader: (2)

Tink, verify the dist timing 1 more time with scan tool. If you are 100% confident the compression is ok (if one cylinder varies from the others 30 psi...) then you need to pull the distributor and examine the drive gear. It shouldn't be that bad since its a Van. Make sure u rotate the motor and look at the entire gear.