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I’ve had a few reports of that engine having trouble with fuel injectors, I would recommend first doing a power balance test just to see if the problem is the result of a particular cylinder(s), if you find one then I might look to the injectors on that cylinder. I don’t think it’s a bad idea to check the fuel pressure as well especially a shut off test to observe if the pressure is dropping after shut down which could be the result of a leaking injector. Lastly lets not rule out an ignition issue and check for leaks in the system just for good measure.
Welcome to the forums!
+1 to everything Eric said.
What do the fuel trims look like when the idle starts to drop as well as o2 readings?
Ok, answer to all so far:
Trcustoms719: Coolant temp is reading properly, rises as the engine temp goes up. There are no more vacume leaks 🙂 Checked every single hose and connection. Also the IAC counts do not indicate a leak. The IAC counts actually rise when the concern occurs to compensate for the low idle.
EricTheCarGuy: Have not done a power balance test as of yet. The window of opertunity is very small. I’ve seen the same reports about debris in the fuel injector screeens, my only concern with this is: This situation only occurs for 20-30 seconds after the engine goes into closed loop then clears up. I cannot duplicate it driving under load, brake torque (not burning the tires:), in overdrive (coasting,accel, or decel). I would think injectors would be a little more persistant. I did check fuel pressure. If I remeber correctly, it was 50psi engine running and did not drop with the key off. I did wet test the cap and ignition wires, ok with that test, also checked all of the spark plugs, all ok.
dreamer2355:Thank you for the welcome 🙂 I’m glad I finally made it here 🙂 Long term fuel trims drop to between -4 and -8 and the O2 really drops to between 125 and 93 then stays there until it smoothes out. And is fine after that. I know it is indicating a lean condition, just not sure why for such a short time.
One other thing I checked was timing chain free play. And it is pretty high in my opinion (about an inch from mark to mark). Thanks for all of the help so far guys 🙂
Just to focus the thought process, it seems we should be gathering info on what happens when the engine exits warm-up mode and goes into closed loop. At that time the computer is going to try to lean out the mixture somewhat and it will begin to factor in the o2 sensor. So what are the short term and long term fuel trims before, during and after the event? What is the o2 sensor showing and how quickly is it switching? The numbers you gave for the o2 above don’t make sense to me… it should be switching between about 0.2v and 0.9v.
Finally, are you saying the timing chain has slack? That would tend to mess things up because the cam timing woul be off
Rick: The long term F.T. are pretty normal before and after the event, I really don’t pay too much attention to S.T. Rhe O2 sensors after the event switch rapidly (my scan tool shows the O2 sensor voltage beteen 00 and 1000 mV for this application, others read properly). And yes, the timing chain has slack in it Original chaim w/160K miles). That’s what I was thinking, I just wanted some verification that the chain could possibly cause this comcern and then the ecm compensates and smoothes out the rpm’s.
If the timing chain is that slack, that may contribute to that condition due to timing issues.
I would look at the timing on your scan tool during start up and particularly when this issue happens.
Did you check the integrity of the o2 sensor wiring?
Do both banks show a lean condition when graphing your o2 sensor readings?
How is the o2 heater circuits?
dreamer2355: The cam position sensor goes haywire when tapping the throttle. O2 sensor wiring is ok, and I only have bank 1 on the scanner. I am not sure if this truck has O2 heaters to be honest. I would think it should being obd2.
You should have bank 1 and bank 2 heated pre-cat 02 sensors.
If the cam sensor is reading erratic, that could be down to the timing chain slack. I would see what the spec is for timing chain stretch.
Quoted From dreamer2355:
You should have bank 1 and bank 2 heated pre-cat 02 sensors.
If the cam sensor is reading erratic, that could be down to the timing chain slack. I would see what the spec is for timing chain stretch.
+1 on this because engine mechanical should never be ruled out when dealing with performance issues especially with the evidence you have with your crank sensor readings.
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