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87s-10 iron duke 4 speed
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38 Posts
Discussion Starter #1
2000 Gmc Jimmy 4x4 Tow Package 164000 Miles
Last month or Two, The Jimmy picks and chooses when it wants to start, some times it wont start, then other times it will start with no problems for a week or so then back to not wanting to start. When it Does run the power is normal, good acceleration, Terrible fuel Economy (low 13mpg city, 15 mpg highway always speeding). The check engine light Is on and these are the codes: PO171 Lean Bank 1, PO174 Lean Bank 2, PO304 Cylinder # 4 Misfire(usually not on, randomly comes and goes this code does)


Lately the ONLY to get it to run is turn the engine over, release the key it sometimes Runs for a few RPM's then real quick turn the key to start position and it will sputter for a second then actually run after I rev the engine to 3-4k rpms a few times, and then runs like a top, again once it starts it runs and drives fine.



The Check E light has been on and off since ive had the vehicle, and this is what i have done in the last 40kmiles:
Spider Injector upgraded version (was sputtering while acceleration and running Terrible at idle)

Fuel Pressure Regulator

Mass Flow sensor (ran smother and better power/acceleration)
All 3 O2 Sensors (ran smother and better power/acceleration)
Plugs (Iridium "Think" ACDelo ignition parts ), Cap/Rotor, Wires, Coil



Flush coolant system(chemical, flush then with flush kit several weekends in row, water kept coming out nasty AF, drained and refilled with 50/50 dex cool) Replaced Bottom Fan shroud, Fan, Fan Clutch, Water Pump, OEM Thermostat, Belt for pulleys, (used to like to jump over 210 mark quick at idle at lights or drive through and leak antifreeze), and Both hoses to and from Radiator.


Coolant temp sensor
Few other sensors that i cant remember

Think only vacuum line to brake booster
And other Wear and tear parts





Sorry for list, previous owner didn't know what maintenance was. Oh Yeah, do NOT buy at a mom and pop used car lot, trust me terrible idea.


Question is How do i make it Start Normally where i don't gave to play ballet with the key and ignition to get it to run?


Probably the Original Timing Belt, could the timing be off due to worn timing belt? Or????
 

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time to get cereal
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1,990 Posts
You have a timing chain, and if it's original, I'd replace it whether or not it's the cause of your problem.
 

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Registered
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1,137 Posts
2000 Gmc Jimmy 4x4 Tow Package 164000 Miles
Last month or Two, The Jimmy picks and chooses when it wants to start, some times it wont start, then other times it will start with no problems for a week or so then back to not wanting to start. When it Does run the power is normal, good acceleration, Terrible fuel Economy (low 13mpg city, 15 mpg highway always speeding). The check engine light Is on and these are the codes: PO171 Lean Bank 1, PO174 Lean Bank 2, PO304 Cylinder # 4 Misfire(usually not on, randomly comes and goes this code does)


Lately the ONLY to get it to run is turn the engine over, release the key it sometimes Runs for a few RPM's then real quick turn the key to start position and it will sputter for a second then actually run after I rev the engine to 3-4k rpms a few times, and then runs like a top, again once it starts it runs and drives fine.



The Check E light has been on and off since ive had the vehicle, and this is what i have done in the last 40kmiles:
Spider Injector upgraded version (was sputtering while acceleration and running Terrible at idle)

Fuel Pressure Regulator

Mass Flow sensor (ran smother and better power/acceleration)
All 3 O2 Sensors (ran smother and better power/acceleration)
Plugs (Iridium "Think" ACDelo ignition parts ), Cap/Rotor, Wires, Coil



Flush coolant system(chemical, flush then with flush kit several weekends in row, water kept coming out nasty AF, drained and refilled with 50/50 dex cool) Replaced Bottom Fan shroud, Fan, Fan Clutch, Water Pump, OEM Thermostat, Belt for pulleys, (used to like to jump over 210 mark quick at idle at lights or drive through and leak antifreeze), and Both hoses to and from Radiator.


Coolant temp sensor
Few other sensors that i cant remember

Think only vacuum line to brake booster
And other Wear and tear parts





Sorry for list, previous owner didn't know what maintenance was. Oh Yeah, do NOT buy at a mom and pop used car lot, trust me terrible idea.


Question is How do i make it Start Normally where i don't gave to play ballet with the key and ignition to get it to run?


Probably the Original Timing Belt, could the timing be off due to worn timing belt? Or????
Do you have a scan tool or scan app that can read live data?

There is no timing belt, so forget about that idea. There is a timing chain, but you're not describing any symptoms that would make me question the timing chain.

Run a full fuel pressure test. Also, has the fuel filter been changed? If no, or even if you're not sure, put a new filter in when your running the fuel pressure test at the fuel filter. You need to check the peak pressure during prime and the pressure 10 minutes after priming and turning the key off. Check both pressures/times at the schrader valve by the spider, and also at the fuel filter with the pump running straight into the gauge (optionally through the filter). Don't "Tee" into it at the filter, set the gauge up as the end of the line. At the schrader valve, you should have about 60psi peak during prime, and it should fall no lower than 50psi after 10 minutes with the key off immediately after priming. At the filter, directly into the gauge, it should read 75psi (ish) as peak during prime, and it should stay over 65psi after 10 minutes. It may be higher at the filter (measuring unregulated pump output pressure), but in 10 minutes, it should not lose more than 10psi.

Check for vacuum leaks. This is easier (and more precise) with a scan tool/scan app. Watch the upstream O2 sensor voltages ("sensor 1" on bank one and bank two) on graphs. With the engine warmed up (drive it first, then check for vacuum leaks), the sensors should fall into a nice oscillating rhythm. Spray Intake/Throttle body cleaner (NOT Carburetor cleaner!!!)around the intake manifold gaskets, the vacuum fittings/lines, the MAP sensor and purge valve and around the injector spider. If there's any leak at all, it will make the O2 sensor voltage(s) swing way to the rich side when you hit the leak with the cleaner.

Obviously fix any vacuum leaks you find.

I really suspect you've got a fuel pressure issue, though.
 

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Engineer, Member SAE
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22 Posts
Overlooking all the electrical causes...

That sounds like low voltage to either or both the computer (should be immune to that) or more likely, the ignition module. This is an "old vehicle" symptom i.e. one with rotten wiring.

Put a voltmeter on the terminal to the ignition module (and/or coil) and see what the voltage is during cranking- it shouldnt go much below 11-12 VDC and must be 14.8 running.

Thats also the symptom for a bad ignition switch
 

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Engineer, Member SAE
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22 Posts
Thats typical for electrical problems

1. Bad ignition switch
2. Low voltage to the ignition coil and/or the ignition module.

Low or no voltage, or intermittent voltage, during cranking lets the engine load up with fuel, Once it starts running, it runs rough till the excess fuel, that wasnt burned off during cranking and initial start, burns off- then it runs clean.

In the period between the end of cranking and releasing the key, the battery voltage will rise (cranking is around 10-11V) and that is the time when it might catch enough voltage to spark and start. Thats the "it fires when the key is released" part.

Put a volt meter on the 12 V side of the ignition module and coil, the voltage during cranking shouldnt drop more than a few tenths of a volt (depending on whether theres a dropping resistor) from battery voltage. It MUST be 14.8 within a few tenths when running.
 

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Been there Done it
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6,339 Posts
If you're getting lean codes and have start issues CHECK THE FUEL PRESSURE. It's an S-10. Low fuel pressure is the #1 cause for lean codes and intermittent starting. If you don't believe me, next time it won't start shoot a SMALL amount of starting fluid into the air horn on top the throttle body. You can simply pull the breather tube off the back of it and shoot it in there and reconnect the tube. Helps to hold the throttle open about 10% so the engine can swallow the ether. If it fires momentarily, you know the issue is fuel related. If nothing happens try a little more starting fluid. If still nothing start your electrical diagnosis.
Most LAPS have borrow programs for fuel pump testers and it only takes 5 minutes. 30 minutes if you do the leak down test.
There is a sticky on how to or I'm sure you can find a You tube. If you trust them.
 

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Registered
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1,137 Posts
Overlooking all the electrical causes...

That sounds like low voltage to either or both the computer (should be immune to that) or more likely, the ignition module. This is an "old vehicle" symptom i.e. one with rotten wiring.

Put a voltmeter on the terminal to the ignition module (and/or coil) and see what the voltage is during cranking- it shouldnt go much below 11-12 VDC and must be 14.8 running.

Thats also the symptom for a bad ignition switch
Experience says, that's the next thing to check after fuel pressure. On S series trucks and SUVs, the ignition system is far more reliable than the fuel system. That seems to be true for a lot of other 1990s-2000s GM products as well. For other makes with more reliable fuel systems, you might start with the electrical/ignition checks.

Actually, I like the "starter fluid" test. If it runs for several seconds relatively normally on starter fluid, and then sputters (and maybe dies), then it's a fuel related issue, not an ignition related issue. A few squirts of starter fluid will usually get you on the right track.
 

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87s-10 iron duke 4 speed
Joined
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38 Posts
Discussion Starter #10
Mr. JIMMY went from not Running at all to running like a top when i replaced the
Ignition Module, and fuel pressure from valve in engine bay was 57-58 and
Barely (maybe a psi) dropped after 20+ min, check E light off at the moment, will fuel pressure at filter this weekend, filter has been replaced, 3 times (when i first bought vehicle, replaced spider system, pressure regulator) since ive had it.
Will replace timing chain soon also. We'll see if it is actually "fixed" or it just decided to run because it wanted to.
Will continue to test stuff to get it to run better, been fixing crap since ive bought it, Thankyou
 

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Been there Done it
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6,339 Posts
Thanks for telling us what worked for you. It'll help someone down the road.

been fixing crap since ive bought it,
It's an S10.
You don't buy one. You marry it and it starts making a TO DO list the 1st day. Most come with one already started.
 

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87s-10 iron duke 4 speed
Joined
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38 Posts
Discussion Starter #12
Yessir! When i had my 87 S-10 iron duke, was Allways fixing crap, miss that old pos truck sometimes
 
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