Cleaned the MAF this past weekend but still have the rough idle and SES light. Looks like I'll be doing a rebuild unless someone has any other suggestions.

 

I would still lean toward injector issue at that amount of miles.....do they have a flow match machine to determine spray patteren and flow? And to verify no leakage after shutdown?

Here is our machine....priceless when trying to determine injector issues:

One was sticking in this example and dumping fuel into one cylinder:

After rebuilding it and cleaning the rest:

As for a rebuild, that's extreme. These engines will go 300-400k plus with no need for a rebuild if a good full synthetic is used and properly maintained. Is it using a lot of oil?

 

I don't know if they have a flow match machine. The dealer is in Albuquerque and I brought it back to Phoenix. The injector was replaced at 197K. I guess I could swap injectors, clear the code and see what happens Don't know of it's using oil. No mention of it in the service records and I haven't driven it enough to know. I can't pass emissions at this point.

I did notice a knock/clicking noise when accelerating this weekend after cleaning MAF. Couldn't isolate it though. Maybe an exhaust leak?

Forgot to mention, no synthetic oil but my Dad was meticulous with maintenance.

 

I cleaned the MAF and no change. I swapped injectors, cleared the code and I'm now getting a generic P0300 misfire code. I went ahead an changed the intake manifold gasket, cleared the code and drove around the block a couple times and no code. Still idling a little rough though. Drove again a few days later and the P0300 is back.

Tuner Boost is leaning toward injectors so maybe I'll try some injector cleaner.

 

My bet is injector as well. This motors if properly maintained and driven normally which sounds like this truck has been can easily go 250k. Been involved in maintaining a fleet of 50 trucks for close to 30 yrs. and seen alot of these small block GM's go 250k and still running strong when they where replaced because the rest of the truck was worn out.

 

Well I pulled the injectors and made a test jig to clean them out. Measured resistance on them all first and they are all right at 13.1 ohms. Connected a hose to one, put some Sea Foam in the hose, applied about 20lbs of pressure behind the Sea Foam and pulsed the injector. It fired and shot out the Sea Foam. It was a steady stream like out of a squirt gun not a fan type spray like I expected. That may be because the pressure is too low. Anyone know what the fuel rail pressure is on this engine? 8th digit of VIN is a 'T'.

 

Should be about 55-60 psi...Do you have access to a scan tool to look at misfire data? If so, you can look at where your misfire is coming from whether its from cylinder 2 or another cylinder. If its still on #2 Then maybe look at something mechanical like in the valve train or possibly the bottom end...hopefully its just an injector tho!

 

Thanks for the information. I have a scan tool that provides some live data but I don't see anything for misfire. I moved the injector a while back from number 2 to number 6 and the code changed to a random misfire P0300 code.

I raised the pressure last night and cleaned all injectors. 3 out of 7 were somewhat clogged. By that I mean they were not spraying a fan spray pattern but cleared after a couple of pulses. I have one that is clogged on one side and has a half fan spray pattern. It was getting late so I'll see if I can unclog the last one tonight. If I can't, I get another injector. Hopefully this fixes the problem and it's not valve train or bottom end.

 

Last injector cleaned up and had a good spray, Got it all back together and still have rough idle and P0300 code. Got a fuel pressure gauge and checked the pressure. Had 50lbs static and 49 running. As craigger325i said to should be 55-60. I pulled the vacuum line off the FPR and it wasn't leaking so I'll assume that it's good. I guess I'll try a fuel filter first to see if the pressure comes up and if not, I'll replace the fuel pump.

 

Just a though here it sounds like you know what your doing but did you clean the Intakemanifold, and TB? Also when you were in there how did the valves look?

 

I can turn a wrench but I wouldn't necessarily say I know what I'm doing... Just doing a lot of research on this site. I pulled the intake manifold, cleaned everything up and installed a new gasket. I used the sea foam spray with the little hose that you pinch between the TB and intake tube and spray in while you rev the engine but didn't physically clean the TB. I haven't inspected the valves because the dealership did it a while ago. What specifically should I look for?

 

Depends on how often the TB is cleaned, mine was really rough at 112k so it might need a good cleaning after that, also as far as the valves go, look for any thing out of place, bent damaged, odd, If you do go that far, also take note of the carbon deposits in the intakemanifold , if one is cleaner/dirtyer than another your on to something.

 

TB looked really clean but I went ahead and cleaned it anyway. No change. I guess I'll pull the intake manifold again and inspect it again.

 

Didn't have time this weekend to pull the intake manifold. Will do it later this week. I did however change out the fuel filter but it didn't help.

 

did you ever get it fixed. I have had the same issue for the last three months and have replaced every thing from plugs to injector. It works well for a while and then back to the same ol stuff..

 

This is from AllData:

SYSTEM DESCRIPTION
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.

CONDITIONS FOR RUNNING THE DTC
DTC P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0125, P0128, P0220, P0315, P0335, P0336, P0341, P0342, P0343, P0502, P0503, P1114, P1115, P1120, P1258 are not set.
The engine speed is between 450-5,000 RPM .
The ignition voltage is between 10-18 volts .
The engine coolant temperature (ECT) is between -7 and +130°C (19-266°F) .
The fuel level is more than 10 percent .
The throttle angle is steady within 1 percent .
The antilock brake system (ABS) and the traction control system are not active.
The transmission is not changing gears.
The A/C clutch is not changing states.
The PCM is not in fuel shut-off or decel fuel cut-off mode.
The PCM is not receiving a rough road signal.

CONDITIONS FOR SETTING THE DTC
The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.

ACTION TAKEN WHEN THE DTC SETS
The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:
Thickness variation of the brake rotors-Refer to Symptoms - Hydraulic Brakes. See: Brakes and Traction Control\Disc Brake System\Testing and Inspection\Component Tests and General Diagnostics
The drive shaft not balanced.
Worn or damaged accessory drive belt.
There may be more or less cylinders actually misfiring than indicated by the scan tool.
Spray water on the secondary ignition components using a spray bottle. Look and listen for arcing or misfiring.
If there are multiple misfires on only one bank, inspect the fuel injector and ignition coil, power and ground circuits for that bank.

 

I let this project sit for a while as I just didn't have time to work on it. I finally got back on it last month and ended up taking it to a shop for a second opinion. The #2 cylinder was down to 50lbs compression. So I opted to get a used engine out of a 2004 Tahoe with 100k miles and all 8 cylinders reading 180lbs compression. While I was at it, I got a rebuilt tranny as the original was starting to slip. Dropped the engine and transmission in this past weekend and I'm in the process of hooking everything back up. Hope to have it running this weekend.

 

Hi Allansivell,

I'm sorry to hear that you are also experiencing this concern. We will be glad to look further into this for you. Feel free to send us a private message referencing your concern if we can be of any assistance. We will be glad to help!

Kristen A.
GM Customer Care