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Old 09-12-2010, 08:52 PM
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Re Truck died, so coasted into parking,

My 94 GMC Jimmy 4.3L Vortec 6cyl, 5 speed sputtered on the way home one day, It was late, and getting dark, would have been towed A LONG LONG WAY, I decided the Injectors were lacking a signal, so I grounded one It ran-- I got home, since then, It refuses to start, It cranks very fast, It has spark, it has fuel pressure, (I drove home), but now the injectors will not release fuel.
I checked all the fuses, (they are under the dash) not firewall.
I put a new temp sensor.
I put a new TPS.
I put a new Ignition Module,
I put a rebuilt ECM.
I charged the battery till the charger, read nearly zero current.
I put a new alternator.
Dont want to buy an OBD scanner, the good one, would only be used once!
It still cranks, has spark, no injector opening.
Does anyone have an Idea what signal, the computer is waiting for to fire the Injectors, The tranny is standard, I dont think anything but the speedo sensor is there.
And I cant find a schematic that really matches the truck wiring,

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Old 09-13-2010, 06:11 AM
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I know you mentioned it has fuel pressure. However.....I had to replace a couple of fuel pumps in my 4.3 Blazer over the years. I actually kept a spare with me 'just in case'. The fuel pumps are notorious for quitting at the most inopportune time. My advice for what it's worth....check the fuel pump. Good luck.
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Old 09-13-2010, 10:40 AM
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[QUOTE=randolphi]My 94 GMC Jimmy 4.3L Vortec 6cyl, 5 speed sputtered on the way home one day, It was late, and getting dark, would have been towed A LONG LONG WAY, I decided the Injectors were lacking a signal, so I grounded one It ran-- I got home, since then, It refuses to start, It cranks very fast, It has spark, it has fuel pressure, (I drove home), but now the injectors will not release fuel.
I checked all the fuses, (they are under the dash) not firewall.
I put a new temp sensor.
I put a new TPS.
I put a new Ignition Module,
I put a rebuilt ECM.
I charged the battery till the charger, read nearly zero current.
I put a new alternator.
Dont want to buy an OBD scanner, the good one, would only be used once!
QUOTE]
Looks like your getting close to spending the money, guessing .... got fuel flow from the tank? Have you verified it, just because you drove it home means nothing, there are intermittent problems that can occur.
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Old 09-13-2010, 11:01 AM
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You can rent a scanner at most of the chain auto stores. You also need a listing of the trouble codes.
www.alldatadiy.com is a good source for a shop manual.
But I sounds like the crankshaft position sensor or camshaft position sensor is bad. These sensors are for engine speed and crankshaft position to trigger the PCM when to fire the injectors and fire the ignition. Without these inputs the PCM will not function.
The crankshaft position sensor is located on the engine front cover perpendicular to the crankshaft target wheel.
A resistance test can be done by disconnecting the connector and probing the sensor side of the connector. Reading should be 800-1200 ohms. If these reading are not in this range the sensor is bad.
Any further tests of the sensor require a scan tool.

To test the fuel pump you need a pressure gauge with the proper fitting to attach to the test fitting on the fuel rail.
Turn ON the ignition. The pump should run for 2 seconds and the pressure should build up and hold after the pump stops. On TBI engines pressure should be 9-13 psi.
Multi-port engines 41-47 psi.
If no pressure - check, fuse, relay, ground and power to the pump.

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Old 09-13-2010, 06:16 PM
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Quote:
Originally Posted by randolphi
My 94 GMC Jimmy 4.3L Vortec 6cyl, 5 speed sputtered on the way home one day, It was late, and getting dark, would have been towed A LONG LONG WAY, I decided the Injectors were lacking a signal, so I grounded one It ran-- I got home, since then, It refuses to start, It cranks very fast, It has spark, it has fuel pressure, (I drove home), but now the injectors will not release fuel.
I checked all the fuses, (they are under the dash) not firewall.
I put a new temp sensor.
I put a new TPS.
I put a new Ignition Module,
I put a rebuilt ECM.
I charged the battery till the charger, read nearly zero current.
I put a new alternator.
Dont want to buy an OBD scanner, the good one, would only be used once!
It still cranks, has spark, no injector opening.
Does anyone have an Idea what signal, the computer is waiting for to fire the Injectors, The tranny is standard, I dont think anything but the speedo sensor is there.
And I cant find a schematic that really matches the truck wiring,
You spent a lot of money just guessing at it. your first guess was probably a good one. If you had no injector pulse you grounded an injector and it ran then the fuel pump is obviously good
Secondly all the extra fuel from the injector sprying constantly probably washed the oil film off the cylinder walls and now it cranks faster due to low or no compression.Pull the plugs and let it air out by cranking it over for a minute and put a few shots of oil in the cylinders and crank it again to spread it around.
Did you remember to install the prom in the new ecm? very important.Also the backup chip( should have been in it allready actually)
Also i have seen pickup coils that would spray an injector but was not strong enough to fire the coil in start up mode. Did you verify that the injectors have the 12 volts + at them with the key on. The power for them will come from the ECM 1 fuse in the fuse box. It goes through the ignition switch and is supplied through a fuse link at B + ( 12 volts) sounds like you do as the engine ran when you supplied a ground.with everything you have allready replaced i would put a pickup coil in it if I were to guess, but I would recommend checking for codes by jumpering the 2 pins in the aldl.You should disconnect the battery after checking them to clear them if you get any codes relating to pcm failure and then power the system back up and recheck for the same code to re appear.After having all the sensors unplugged with the key on you will have a lot codes that are "false" or falseley generated and stored.

Last edited by latech; 09-13-2010 at 06:28 PM. Reason: wrong info 3rd paragraph
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Old 09-13-2010, 06:32 PM
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By the way I assume you have the "Z" engine code and not the "W" CPI engine
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Old 09-13-2010, 06:35 PM
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Something that just occured to me is that a wide open throttle posistion signal will shut the injector pulse off as the throttle sensor full output would signal the ecm to Clear flooded engine. If the tps signal wire is shorted to reference voltage it will shut the injectors off.Also the distributor hi reference or low reference wire being open would also not fire the injectors.
The distributor generates the signal that runs the system there is no "crank " sensor per se'

Last edited by latech; 09-13-2010 at 06:48 PM.
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Old 09-13-2010, 07:12 PM
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Thanks for all the great tips you guys!!
Well I wont have time to try all these ideas till, the middle of the week.
I believe fuel pressure is ok I got home, that night, running nearly 50 mph on one side of the tbi, I dont think that grounding the injector would make the fuel system, behave that abnormally.
It is the Z model.
Reading codes, (the engine has to run to set most of them), when I tested the connectors, they set codes, when I clear the memory, now And start for a short time with, starter fluid, all she says is 12 12 12 12 12.
Heres something odd though, when first turning key to on, all the lights test like normal, but when cranking, the little battery shaped light goes off then, still cranking, flashes twice, pause then three times, probably nothing!
It has a camshaft position sensor type distributer.
Would the oil/pressure fuel pump/relay swt. cause the computer to shut off the injectors?
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Old 09-13-2010, 07:36 PM
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Quote:
Originally Posted by randolphi
Would the oil/pressure fuel pump/relay swt. cause the computer to shut off the injectors?
No it wont.The ecm grounds the fuel pump relay to run the pump for 2 seconds when turning on the key. After the engine starts the oil pressure switch contacts close to power up the pump circuit,neither one has any effect on injector pulse.
Some codes will be stored in the ecm without the engine running.Codes for things like Throttle sensor map sensor coolant sensor will store just by turning on the key if there is a problem electrically. Try it out. clear the codes and unplug the coolant sensor turn on the key and then look for a code. If the ecm is working properly it will generate a code for the coolant sensor signal too low or code 15.
Any sensor on the engine that runs the engine in open loop will set a code without having the engine running just by turning on the key if the sensor signal is ouside of its parameter for current operational condition.
If the ecm wont set a code then it has at least one problem.There are a lot of different ways to determine if an ecm is bad.too many to list here at the moment. dont get to far ahead of yourself.
I would take a good look at two things for starters first. Make sure that you are reading the code correctly as a code 12 is normal without the engine running. If you are counting check engine light flashes and you are out of sync that code 12 could be a 21. 21 is for the tps volts high and that will cause the injectors to shutdown as the ecm is seeinga clear flooded engine request from the value given by the tps. I see you replaced the tps but if the gray and blue wire in the tps harness have melted insulation and the wires are touching it will also cause this . It does happen

Last edited by latech; 09-13-2010 at 07:54 PM.
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Old 09-15-2010, 07:12 PM
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Tps

I checked the tps swt today.
With the throttle closed, it showed .5 v and wide open, It went to, 4.74 v.
Seemed ok to me.
Do knock sensors, have to be good, before the ECM will signal Injectors?
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Old 09-16-2010, 08:35 PM
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Gee, flooded engine, how does that happen?
I thought full open throttle meant, go faster!
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Old 09-16-2010, 08:41 PM
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Quote:
Originally Posted by randolphi
Gee, flooded engine, how does that happen?
I thought full open throttle meant, go faster!
Flooding can occur if an injector sticks or say the fuel pressure regulator diaphram starts to leak or if liquid fuel gets past the check in the evap sytem. It happens . WOT with the engine running will go faster real good, but wide open throttle with the engine cranking to start will clear flooded condition.
Sounds like the TPS readings are right about where they should be, no problem there.
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Old 09-16-2010, 08:42 PM
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Knock sensor only affects timing.Will not affect the injectors.
Have you also verified fuel pressure while symptom occurs?

Last edited by latech; 09-16-2010 at 09:10 PM.
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Old 09-29-2010, 09:23 PM
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Thanks for all the Help!!

All of the suggestions, helped me, In rethinking about the events, the day, that the truck first stopped running right, I was too quick to decide that the injectors were not operating correctly.
I missed the fact that the prime cycle of 2 seconds, did make the engine "almost" start momentarily, repeatedly.
This verifies the pulsing from the computer.
The other misleading, idea, was that, because I made It run, by constant ground to the injector, fuel supply was good.
Only a slight dribble of fuel will make the engine run!
So, knowing that "steady" pressure is required for the fuel system to operate.
I pulled the fuel tank, removed the fuel pickup,w/pump assembly, and was astonished to find that the pump had been installed, at sometime, without CLAMPS on the hose that connects the pump to the supply tubing.
And the flow from the pump had "pushed" the hose further up the Line, Untill, It was just above the pump, and allowing the fuel to spray right back Into the tank.
I put in a new pump, just because I had allready removed the tank,
and with it that far apart, no sense In using the older pump.
It started right away, and Idled better than It has in several months.
So THANKS AGAIN FOR ALL THE SUGGESTIONS!!
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Old 09-29-2010, 09:29 PM
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