Intermittent long crank before start

[movietvet]

Was just informed today by my girl, that her 2002 TB 4.2 recently started to crank longer before starting and a couple times she released the key and then cranked again and then would start and seem to falter at idle for a couple seconds. Only happens after been sitting for a longer time, like overnight.

I fear a fuel bleed down after sitting long enough. Gonna test pressure at fuel filter when have better weather and have told her to turn key to KOEO for 10 seconds and then try to start. I drove today with no problems, starting or idle. I fear maybe a pressure regulator but see no leaks there and will check further. Any known problems for the first year TB's, that you guys/girls can share, that might be related or sound like what I am experiencing?

Thanks

 

[Mooseman]

Check the fuel pressure. Same thing happened to me, which was caused by a leaking fuel line. Either you have a leak or the pump is failing.

 

[X831X]

I had this issue a over 10 years ago on my TB. My mechanic said failing fuel pump, replaced it & has been good ever since.

 

[TollKeeper]

So what they are saying, run her low on gas, so you can change the fuel pump!

 

[movietvet]

I am thinking fuel pump or pressure regulator leak down or an extreme possibility is a leaking injector.
Just the one side of the regulator that I can see does not show a "clean" section, indicating a leak but I cannot see the whole thing where it is mounted. I am one of those guys that if I do the pump I would do the regulator too and the fuel filter but the filter is less than 200 miles old. I do have a fuel transfer pump to allow me to empty the tank if needed. I will be doing a pressure test and then shut off to look for a bleed off. Likely tomorrow. Thanks for the info. If I do the fuel pump, I will be doing the fuel tank pressure sensor too, while in there. I know that has nothing to do with my problem but I am that way about replacing parts, "while I am in there".

 

[mrrsm]

Three more symptoms to add onto the List of Problem Possibles:

(1) Poor or Loose Ground Cables- Bonding Straps (and at G-107 on the Engine Block)..
(2) Low or Poor Cylinder Compression...Excess Top Rings Carbon "Glue" trapping them.
(3) Leaking Intake or Exhaust Valves. Excess Carbon Build Up is also the culprit here.

A Failing Fuel Pump can be painlessly diagnosed without its R&R ...at the Fuse Box... by inserting a Fused Loop into the Fuel Pump Fuse location and then encircling the Loop with a Low Amp (Current) Clamp attached to Channel #1 of an Oscilloscope.

The Low Amp Clamp BNC Connection allows the signals from the Fuel Pump to be picked up as an intermittent Amperage Draw and then viewed on the Oscilloscope Screen. This procedure will NOT work using an ordinary (Non-Graphing) DMM.

The correct Electrical Pattern that should show up on screen is a Narrow Up & Down Zig-Zag Pattern that hovers around 6-8 Amps (Converted from DC Voltage in the Software) on the Vertical Axis... with NO Breaks or Cut Outs in the cycles of the Up & Down Zig-Zags in the Horizontal (Time) Axis. If those artifacts appear, it indicates that the Fuel Pump is under Stress.

By looking over the Horizontal (Time) Pattern for Repeat Unique markings in those Zigs & Zags ...every 360 Degrees of Pump Rotation will produce either 8, 10 or 12 Commutator Events depending upon how many the OEM Manufacturer has built into its design, Observing this action allows you to determine the Health of the Fuel Pump.

THIS is what a "Healthy" Good Known Fuel Pump Wave Form SHOULD look like:



And Post-Diagnosis Results Display the GOOD Wave Form over The BAD Wave Form:



Eric "O" from South Main Auto (SMA) up in Avica, NY Demonstrates what you see above by following this Simple Oscilloscope Diagnostic Procedure that will work on ANY Vehicle just as well with ANY inexpensive Hantek Model #1008C or the PICO-Scope Model #2204A versions:

 

[movietvet]

@mrrsm, would any of your ideas change if you knew the TB has only 70k miles on it and had one owner before us and he did really good on the maintenance and needed repairs?

 

[Mooseman]

If I do the fuel pump, I will be doing the fuel tank pressure sensor too, while in there.

New pumps come with the sensor. Recommend Bosch or ACDelco.

I wouldn't know how to test the FPR. Maybe squeeze off the rubber return line and see if the pressure goes up and stays up as it could also be the one way valve in the pump module. If the pressure is low, block off the return line, if it goes up, I'd suspect the FPR, if it stays low, I'd go with the pump, if it goes high and bleeds down, probably it's the one way valve in the pump.

Without an advanced scanner, it's difficult to verify a leaky injector.

We'd need a flowchart to troubleshoot this. There may be one in GM-SI but mine is down right now.

 

[mrrsm]

Generally, Failing Fuel Pump Pressure Regulators either Leak enough Fuel to make it the Prime Under-Hood Suspect that can often be difficult to locate as the source... OR...it will not provide the reliable 50+ PSI at the Fuel Pressure Schrader Valve whether at Idle or when the Engine is under load.

As far as The Testing Methodology being different for a "Youthful" GMT360 LL8 Motor (and Fueling System) ...the Method Eric "O" describes in the Video really is THE fastest, least invasive and most conclusive test of any Fueling System Integrity, Amperage Draw, Fuel Pump RPM and of course Electric Motor Health.

As long as the Fuel Pressure Test Gauge also reads Nominal to HIGH and a Good Health Report comes from the use of an Oscilloscope, the two tests would eliminate the need to change out the pump. Otherwise... even with using any other Diagnostic Method... it becomes "Making a Best Guess" that may turn out to be an unnecessary, complicated, labor intensive and of course, ...expensive repair, assuming you spend the money to get an OEM Quality Replacement Fuel Pump.

I would look over everyone's practical advice offered in this Thread and then follow the logic of Checking the Easiest Things FIRST. Then, by a process of elimination... work your way towards any need to go beyond with performing the more complicated diagnostic steps. Try not to jump around.. Start with the Simple Steps ...but be thorough and methodical as you proceed.

 

[movietvet]

@Mooseman, I had already looked at the correct Genuine GM, Delphi or Bosch fuel pumps and do not see the Fuel Tank Pressure Sensor. I looked and saw the two lines and the connector for the power. I looked up the sensor itself and it looks like it mounts in to the top of the tank area and you tube videos show same.

 

[mrrsm]

Here is a helpful General View of the (FTPS) Fuel Tank Pressure Sensor Location on top of the GM Fuel Pump:



THIS is the Preferred Method for making a Non-Invasive Relative Compression Test using the FREE PICO-Scope Version 6 Automotive Diagnostic Software and an Inexpensive PICO-Scope Model# 2204A along with a Hantek High Amp (Current) Clamp:

And some On Topic "Class Room" PICO-Scope Basics from Paul "Scanner" Danner at around 28:30 into THIS Video:

...and THIS Link describes specifically How To Perform a MANUALLY INTENSIVE Compression Test using an Analog Gauge on the GM LL8 I-6 Engines:

How To Test Engine Compression (2002-2009 4.2L Chevrolet TrailBlazer, GMC Envoy)

troubleshootmyvehicle.com

 

[movietvet]

@mrrsm, I looked and did not see that but will look closer. If is what I saw, the hole is there to mount it but sensor not with pump module. But I will check closer

 

[Mooseman]

but sensor not with pump module. But I will check closer

My bad. My 07 does have the sensor on the top of the fuel pump module. It's been a long time since I did my 02. Found this pic on eBay of an 02 tank and it's mounted to the rear and left of the filler neck. Looks to be accessible with the tank in place so maybe replacement is not needed.

 

[movietvet]

My bad. My 07 does have the sensor on the top of the fuel pump module. It's been a long time since I did my 02. Found this pic on eBay of an 02 tank and it's mounted to the rear and left of the filler neck. Looks to be accessible with the tank in place so maybe replacement is not needed.

View attachment 106952

If I have to drop the tank, I would be replacing that sensor simply because it is exposed. As I had said before, I am a guy that will replace a part because of exposure and not simply because it is a bad part.

 

[Chickenhawk]

I had exactly the same symptoms as you, accompanied by an occasional faint smell of gas near the gas tank. The top of the gas tank is prone to corrosion, and it took a look with a camera and finally dropping the tank to confirm. It took a new locking bracket, new fuel pump and one new fuel line to fix.

If the problem is corrosion on top of the tank, there is almost no way to remove the lines or the locking bracket without destroying the fuel pump, so if you find this is the source of the gas leak, be prepared with new lines, new bracket and new pump.

It was strange that the metal parts corroded so bad I could occasionally smell gas but it never threw a code.

 

[movietvet]

I had exactly the same symptoms as you, accompanied by an occasional faint smell of gas near the gas tank. The top of the gas tank is prone to corrosion, and it took a look with a camera and finally dropping the tank to confirm. It took a new locking bracket, new fuel pump and one new fuel line to fix.

If the problem is corrosion on top of the tank, there is almost no way to remove the lines or the locking bracket without destroying the fuel pump, so if you find this is the source of the gas leak, be prepared with new lines, new bracket and new pump.

It was strange that the metal parts corroded so bad I could occasionally smell gas but it never threw a code.

Luckily, I have no rust or corrosion on this vehicle. I am in the PNW where salt is not used on roads and the rig only has 70k miles on it.

 

[Reprise]

My bad. My 07 does have the sensor on the top of the fuel pump module. It's been a long time since I did my 02. Found this pic on eBay of an 02 tank and it's mounted to the rear and left of the filler neck.

This gave me an idea...

I'm still 1/4 tank away from being able to completely fill the '03 Sierra's tank. (when I got the truck, the pump started kicking off at 1/4 full -- so all of the stuff I've replaced has gotten me up to 3/4 tank before the pump shuts off).

When I replaced the fuel pump (for several reasons, but not for this issue), I noted that this sensor wasn't hooked up to the old pump, which had a sensor (a Carter), nor there was a harness / plug to attach to the new pump. So my sensor for the Sierra may (?) be at the back of the tank, like the early 360s / 370s. Will have to get under there and check it out.

If it is in-tank (vs. in-pump module), I'm inclined to extend the plug / wires from the back of the tank to the (currently unused) sensor in the pump. Or, take out the one that's in the pump and relocate it to the back of the tank (it's effectively the same part, just relocated over the years). I'd then have to plug the hole where the sensor went in the pump module, but that shouldn't be difficult.

Only issue I found was on Rock, where for both the 2500HD and my 1500HD, there's a note on the Delco replacement that it's not for vehicles with RPO FE9 and GVWR over 8600 lb. My GVWR is 8600 lb exactly, and I just looked at my pic of the SPI / RPO label -- it has FE9 (Federal Emission Certification).

Anywho... thanks for posting this, as it may be the solution to my 'last 1/4 tank' issue. Fingers Crossed, as I'd prefer to have a usable 26 gal tank, vs. a roughly 20 gal tank (those five gallons are valuable when you're getting 8mpg with a trailer on the back!)

 

[movietvet]

Ok, today I got the fuel pressure gauge on the 2002 TB. When I put the gauge on it and just turned key to KOEO, it went immediately to 54 psi and then I started it and the pressure stayed at 51 psi while idling. Then I walked away and left it for an hour. Pressure dropped to 38 psi and was holding at that point. I see a fuel pump replacement when the weather warms up around here and I have a nice sunny day. I did pull the fuel pump relay and of the 4 prongs one looked slightly discolored/darker. I replaced it with a new relay and will monitor it. Thoughts....suggestions?

 

[movietvet]

The fuel pressure regulator is filthy but I see no area, where I could actually see it, that showed no signs of a clean area where fuel would have leaked. I am gonna replace it anyway.

 

[Mooseman]

Pressures seems OK and I think within spec. You did mention that this was an occasional occurrence of the long crank? Maybe the regulator is sticking occasionally? How did it start this time with these pressures?

 

[movietvet]

Pressures seems OK and I think within spec. You did mention that this was an occasional occurrence of the long crank? Maybe the regulator is sticking occasionally? How did it start this time with these pressures?

Started right up but I feel that the pressure would have bled all the way down if left long enough. It was about 45 minutes and lost 12 psi. I know for a fact that my Tahoe does not do that. I plan to do the regulator and retest it and let sit for 5-6 hours. Shall see and report here after.

 

[mrrsm]

THIS Video shows an interesting "Short Hand" R&R Technique that sidesteps any need to remove any other components in order to accomplish this Task:

 

[Mooseman]

To check if it's the FPR or the one way valve in the pump, do this method of checking the pressure.

Would hate for you to replace the FPR, which is fairly pricey, and it winds up being the pump.

 

[MD_Envoy_Driver]

Have you replaced the fuel filter?

 

[TJBaker57]

I'm not sure I would say it is easier to take apart the fuel lines up at the engine versus unscrewing the test port cap. That is assuming you do not have the underbody tank shield option like mine does. That option does make it a pain to access the fuel filter as well as the test port.

 

[TJBaker57]

check if it's the FPR

I have always been a bit baffled by the FPR on the 2002. It is not connected to intake manifold vacuum, it is not even connected to throttle (ported) vacuum, which doesn't even seem to be a 'thing' anymore! It is only connected to the the resonator which should only be subject to significant vacuum if the air filter is clogged!

I see an experiment in my future. I'll tee in a MAP sensor to this 'vacuum' and have an arduino read its' and output to my Torque Pro (or Car Scanner) to see just what we see there!

 

[Mooseman]

It might just be for in case of leakage, it would go into the intake. I have a similar looking FPR on my sled and it just vents to atmosphere.

I suggested hooking up to the fuel line at the rail simply to test the pump's internal valve, taking the FPR out of the system. Pump seems to be working fine, pressure is bleeding off somewhere.

 

[mrrsm]

Looks Like...The Next Stop Might Be... Leaking EFIs... IF the Engine Chugs Along right after Start Up.

 

[mrrsm]

The "Classic" 2002-2003 GMT360 Fuel Pressure Testing Video from @MAY03LT ...

 

[movietvet]

THIS Video shows an interesting "Short Hand" R&R Technique that sidesteps any need to remove any other components in order to accomplish this Task:

I did watch this video and another that removes the air box. It does not look hard to replace the pressure regulator at all. The one that is quoted here has to reach in with needle nose pliers to remove the screw and I also assume he has to reinstall the screw during reassembly. Great way to drop a screw. If I did it that way, I think I would use a flexible set of mechanical fingers. Notice that he did not show the screws reinstall. My plan is to always work smart and not hard. "I got this".

 

[movietvet]

Replaced the fuel pressure regulator today and then installed a fuel pressure gauge on the port at the filter under the rig. KOEO and pressure went to 52 psi, started the engine and it went to 50 psi and stayed there, shut off and was at 50 psi and let sit for an hour and pressure in system dropped to around 30 psi. I started the rig with no problem but while doing repeated start and let idle and shut off and start again, a couple things happened. Intermittently the engine would crank for longer than normal before starting, for about 2 to 2.5 seconds. That may not seem like a long time but is not the norm for this rig. The other thing that my girl had complained about to me that happened two times to her and only one time today to me, was that while engine was cranking and holding key in the crank position, it would stop cranking and just act like a completely dead battery till I cycled the key again. No the spark plugs have not been changed. Should I assume the OE plugs are good for 100k?

Before anyone says anything about a new ignition switch, I have already replaced the old one with one from Standard Parts, because I could not find a Genuine GM part at the time. I could reinstall the old one, I saved it, and see if the problem goes away. I will be checking my battery connections, cables for corrosion under the insulation, voltage drop and connections at starter.

I think I see a new fuel pump in my future work for her. Tough to consider that since the rig has only 70k miles on it but is 21 years old.

Thoughts?

Before anyone asks, no I did not see any "clean spot" "fuel leak" spot on the fuel pressure regulator.

I am kind of mad at myself for not pinching off the fuel return line while I had the gauge on it.

 

[budwich]

Well the "stops cranking" one is pretty tough if it happens "here and there".... makes it hard to do any test setup for a specific period of time / testing effort.

The key / switch doesn't basically do anything other than cause a "signal" to the PCM.... which detects a voltage and then sends a ground (I think) to the start relay. What dash observations do you have during the "event"?

My guess is the start relay has an issue... basically dropping for what ever reason and since the pcm doesn't know that, it keeps the ground on which does basically nothing. You would have to turn the key back (from start to run at the very least).... that's another important observation, you said you have to turn the key OFF... but is that the "only" state... or does RUN work also? very important.

 

[movietvet]

Did not try to cycle back to run, as all I did was do a complete cycle from off to crank again. I will check the starter relay tomorrow. Thanks.

Also, I did not pay attention to dash cluster when it happened either. It was my first experience of the problem and has been very intermittent.

 

[Mooseman]

Back to the fuel, yeah, it looks like either the pump is failing or at least its internal check valve.

For the ignition switch, seems that ACDelco has dropped out of supplying these since it has been over 13 years when it last rolled off the assembly line. We're now at the mercy of the aftermarket

Our trucks are equipped with, what I call, "flick start". You just flick the key to start momentarily and it will keep cranking on its own until it starts or stops after so many seconds on a failed start. Check to see what it does when you do this. My 02, before it was updated, didn't do that. The PCM may need an update to correct it.

 

[movietvet]

Back to the fuel, yeah, it looks like either the pump is failing or at least its internal check valve.

For the ignition switch, seems that ACDelco has dropped out of supplying these since it has been over 13 years when it last rolled off the assembly line. We're now at the mercy of the aftermarket

Our trucks are equipped with, what I call, "flick start". You just flick the key to start momentarily and it will keep cranking on its own until it starts or stops after so many seconds on a failed start. Check to see what it does when you do this. My 02, before it was updated, didn't do that. The PCM may need an update to correct it.

Fortunately I have a friend that can do the update(s) if needed.