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Hummer H3For the Hummer driver who wants the rugged look and off road capabilities of the Hummer, but in a smaller size and with a more fuel economy friendly engine.
Is Harbor Freight in Idaho? I would be concerned with any drop when considering your symptoms. Get a cheap tester, that doesn't leak and check for pressure drop, it should hold, if it does, eliminate fuel delivery from the list.
Harbor Freight is here, indeed I'll try with a properly functioning tester and let you know.
Updates: Engine gets spark regardless of start or no-start condition. No-start condition persists with the use of starting fluid injected directly into the intake manifold via throttle body.
Unless the starting fluid didn't make it past the intake valves into the engine, it seems the only two other things leading to the issue would be no air or incorrect timing.
Notable symptoms: Engine rev's sporadically while driving (as if I am depressing the accelerator). Light oil seepage (found under the intake manifold, could be from PCV sucking oil into intake or could be pushing past engine gaskets) Engine rarely starts on first "timed" ignition crank sequence. Occasional back-fire during unsuccessful "timed" start.
An idea could be spritzing a tiny bit of starting fluid into each cylinder prior to cranking. The issue with this is the "no-start" condition sometimes goes away for several consecutive successful starts (on first crank). It would be difficult to know for sure.
At start-up, does consumed air enter the intake via the PCV system ("bypassing" the throttle body)? If so, could a clogged PCV line (the one leaving the driver's side cam cover) lead to something like these symptoms?
I believe the crank position sensor is impacted by timing and if the PCM is calibrated for a slightly different timing from the old engine, maybe it is a contributor in some way? I am determined to have a better understanding of how all of this works one day haha.
Random possible contributors: 3.5L injectors on 3.7L engine
3.5L throttle body on 3.7L engine
PCM tuned for old 3.5L engine with no adjustments for the different 3.7L engine
Last edited by Dylan Rogers; Jun 6, 2021 at 02:19 PM.
Update:
Both PCV sources seem clear and have strong suction at idle. (Passenger side PCV nipple sucks into cam cover & driver side PCV sucks air out of cam cover)
(For Raul: some photos of my sleeping platform with the air tank installed behind the driver's seat)
Air tank located behind driver's seat and serving as a support for the sleeping platform. Sleeping platform from the rear hatch. Sleeping platform from passenger's side being supported by plywood "foot".
Harbor Freight is here, indeed I'll try with a properly functioning tester and let you know.
Updates: Engine gets spark regardless of start or no-start condition. No-start condition persists with the use of starting fluid injected directly into the intake manifold via throttle body.
Unless the starting fluid didn't make it past the intake valves into the engine, it seems the only two other things leading to the issue would be no air or incorrect timing.
Notable symptoms: Engine rev's sporadically while driving (as if I am depressing the accelerator). Light oil seepage (found under the intake manifold, could be from PCV sucking oil into intake or could be pushing past engine gaskets) Engine rarely starts on first "timed" ignition crank sequence. Occasional back-fire during unsuccessful "timed" start.
An idea could be spritzing a tiny bit of starting fluid into each cylinder prior to cranking. The issue with this is the "no-start" condition sometimes goes away for several consecutive successful starts (on first crank). It would be difficult to know for sure.
At start-up, does consumed air enter the intake via the PCV system ("bypassing" the throttle body)? If so, could a clogged PCV line (the one leaving the driver's side cam cover) lead to something like these symptoms?
I believe the crank position sensor is impacted by timing and if the PCM is calibrated for a slightly different timing from the old engine, maybe it is a contributor in some way? I am determined to have a better understanding of how all of this works one day haha.
Random possible contributors: 3.5L injectors on 3.7L engine
3.5L throttle body on 3.7L engine
PCM tuned for old 3.5L engine with no adjustments for the different 3.7L engine
AFR is low during startup. More air needed to clear flood, if the injectors are leaking. Again, check fuel pressure leak down, before you blow yourself up with starting fluid.
AFR is low during startup. More air needed to clear flood, if the injectors are leaking. Again, check fuel pressure leak down, before you blow yourself up with starting fluid.
AFR all compared well with your chart (and thank you).
Fuel pressure re-check & leak-down:
Key to "on": from 0PSI to 57 PSI
Key in "on" after 8 seconds: 57PSI to 52PSI
Key in "on" from 8 seconds to 2 minutes: 52PSI to 48PSI (very slow and steady loss of pressure)
With engine running: fuel pressure stays at 57PSI no matter what (whether I accelerate hard, cruise, switch to neutral, or am in park)
Fuel Pressure (Key ON, Engine OFF) 380-410 kPa (55-60 psi)
SERVICE PRECAUTIONS
Relieving Fuel Pressure Caution
Caution: Remove the fuel tank cap and relieve the fuel system pressure before servicing the fuel system in order to reduce the risk of personal injury. After you relieve the fuel system pressure, a small amount of fuel may be released when servicing the fuel lines, the fuel injection pump, or the connections. In order to reduce the risk of personal injury, cover the fuel system components with a shop towel before disconnection. This will catch any fuel that may leak out. Place the towel in an approved container when the disconnection is complete.
The control module enables the fuel pump relay when the ignition switch is turned ON. The control module will disable the fuel pump relay within 2 seconds unless the control module detects ignition reference pulses. The control module continues to enable the fuel pump relay as long as ignition reference pulses are detected. The control module disables the fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and the ignition remains ON.
The fuel system is a returnless on-demand design. The fuel pressure regulator is a part of the fuel tank module, eliminating the need for a return pipe from the engine. A returnless fuel system reduces the internal temperature of the fuel tank by not returning hot fuel from the engine to the fuel tank. Reducing the internal temperature of the fuel tank results in lower evaporative emissions.
The fuel tank stores the fuel supply. An electric turbine style fuel pump attaches to the fuel tank module inside the fuel tank. The fuel pump supplies high pressure fuel through the fuel filter, contained in the fuel tank module, and the fuel feed pipe to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pump also supplies fuel to a venturi pump located on the bottom of the fuel tank module. The function of the venturi pump is to fill the fuel tank module reservoir. The fuel pressure regulator, a part of the fuel tank module, maintains the correct fuel pressure to the fuel injection system. The fuel tank module contains a reverse flow check valve. The check valve and the fuel pressure regulator maintain fuel pressure in the fuel feed pipe and the fuel rail in order to prevent long cranking times.
Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool. Verify the fuel pressure is between 345-427 kPa (50-62 psi) and does not decrease more than 34 kPa (5 psi) in 1 minute.
Circuit/System Testing
Important:
The fuel pump relay may need to be commanded ON a few times in order to obtain the highest possible fuel pressure.
DO NOT start the engine.
Ignition ON, engine OFF, command the fuel pump relay ON with a scan tool and observe the fuel pressure gage while the fuel pump is operating. Verify the fuel pressure is between 345-427 kPa (50-62 psi).
¤ If the fuel pressure is greater than the specified range, replace the fuel tank module. ¤ If the fuel pressure is less than the specified range, test, inspect, and repair the items listed below. If all items test normal, replace the fuel tank module.
Restricted fuel feed pipe
Inspect the harness connectors and the ground circuits of the fuel pump for poor connections.
Verify that the fuel pressure does not decrease more than 34 kPa (5 psi) in 1 minute.
¤ If the fuel pressure decreases more than the specified value, perform the following procedure:
Install the J 37287 between the fuel feed pipe and the fuel rail.
Open the valve on the J 37287 .
Ignition ON, command the fuel pump relay ON with a scan tool and bleed the air from the CH-48027 .
Command the fuel pump relay ON and then OFF with a scan tool.
Close the valve on the J 37287 .
Monitor the fuel pressure for 1 minute.
¤ If the fuel pressure decreases more than 34 kPa (5 psi) within the specified time, locate and replace the leaking fuel injector(s). ¤ If the fuel pressure does not decrease more than 34 kPa (5 psi) within the specified time, replace the fuel tank module.
Relieve the fuel pressure to 69 kPa (10 psi). Verify that the fuel pressure does not decrease more than 14 kPa (2 psi) in 5 minutes.
¤ If the fuel pressure decreases more than the specified value, replace the fuel tank module.
Operate the vehicle within the conditions of the customer's concern while monitoring the fuel pressure with the CH-48027 . The fuel pressure should not drop off during acceleration, cruise or hard cornering.
¤ If the fuel pressure drops off, test, inspect, and repair the items listed below. If all items test normal, replace the fuel tank module.
Restricted fuel feed pipe
Inspect the harness connectors and the ground circuits of the fuel pump for poor connections
First off, thank you so much for all of this. Super helpful!
Are ignition pulses the same as injector pulses? They are mentioned in the AllData sheet, and I would like to know to better conceptualize.
The AllData says to ensure less than 5PSI drop over 1 minute and mine drops 5PSI in 8 seconds, which is certainly an issue (thank you for your previous encouragement to pay attention to this). Then an additional 4PSI loss over another ~2 minutes. Something with fuel delivery is certainly a likely contributor, as you proposed.
The J37287 tool makes perfect sense on checking for leaky injectors. The tool costs as much as new injectors and new fuel pump combined, which is unfortunate. I'm sure I could rig something up, but I am unsure I'm going to haha.
Also, I got my Autel scanner today and completed the crank position variation relearn. It did absolutely nothing to the symptoms (sure did make me uncomfortable rev'ing my engine so high, too).
For injectors, I'm interested in what the differences between the different model year injectors. I imagine the injectors for the 3.7L are larger than the 3.5L ones (which I believe are currently installed). However, model years 06, 07, 08 & (09-10) all have different injectors. Anyone have any insight on this? The best I can think of is the injector sizes are calculated based on engine HP and maybe the HP changed mildly (due to tuning and such) between years? On the same topic, my engine is an '08 but "converted" to an '07 (a.k.a. not running '08+ computer and drilled camshaft position sensor). I don't know if '07 or '08 injector would be "proper."
Oh, and the AllData links didn't work for me, which stinks (not a user).
The more I sit and think about this, the more I'm thinking it is a leaking injector. I know the fuel pressure loss is significant during the non-run scenario, but the fuel pressure does not budge at all while the vehicle is running. This informs my thought of it not being the fuel module. If a leaking injector is putting gas in the combustion chamber and doesn't have the air to burn it, I would be having these symptoms. My only confusion with this theory is how it ALWAYS starts immediately on my second turn of the key to the crank position. What is so special about this little factor?
