Farm truck problems

I know this has nothing to do with tractors, but I figured some of you may have had this problem.I have a 98 chevy 1/2 ton with a 5.7 engine. I"m having problems with the injectors not spraying. The local service station says that it"s the injector module and will cost approx. 1k to fix without even looking at the truck. It was running when I pulled it into the garage,I can see maybe an injector being plugged but for all eight to quit. I"m having a hard time buying. With all this electronic stuff on vehicles these days, I"m sure something could cause this. Does anyone have any recommendations to try before I drop that money? I would like to diagnose it as much as I"m able too, any advice would be appreciated.

I had trouble with my 94-small V8. The local Chev garage put in new cap and rotor and fuel filter and it didn't help' I replaced two fuses under the dash. They are both marked for TBI use. Hasn't bothered since. I think one of the fuses was weak and wouldn't let the computer open the injectorts when I would step on the gas.

Is there fuel pressure at the engine? Might be the fuel pump in the tank is dead or has a shorted wire or a blown fuse. If you just turn the key to the "On" you should hear a hum for a few seconds coming from the tank. No hum, bad pump. My old 1996 5.0 C1500 had the pump in the tank die. Drop the tank and replace. Also the pressure regulator could be faulty.

If it is the same fuel injection system as the 1996 (spider injectors), do the job yourself. Not hard and only takes a couple hours. I bought a new AC injector set-up on e-bay for $250-300, plus the gasket/seal kit from a Chevy dealer for $40. Beats the heck out of 1K.

bob

With Pontiacs we had a problem with the distributor module, would make spark but not send signal from the pickup coil to the ECM.

The ECM would not know the engine was cranking and would not pulse injectors.

Best bet would be to find someone willing to at least check it out. Some shops are not willing to look at a problem, or shotgun it. My mother took her Plymouth to the local dealer to have it repaired, they asked her why not just junk it, it was 8 years old...
She said as soon as you will give me a new one for it in return...

You HAVE to check the fuel pressure. That injection system has spring-loaded poppet valves AFTER the electric injectors and those have to "pop" under adequate fuel pressure, much like a very LOW pressure version of a diesel injector.

If fuel pressure is even 5 PSI LOW due to fuelpump problems, a clogged filter, or stuck fuel pressure regulator the poppets will NEVER open and NO fuel will be injected.

IIRC, (verify this) fuel pressure MUST be 60-65 PSI.

Watch it during cranking to be SURE the pressure stays up even when the battery voltage is pulled down by the load of the starter.

It has 57psi of pressure at the schrader valve, stays the same while cranking. Turned the key off and after an hour the pressure stayed the same, so I'm pretty sure the regulator is good. I just put a new fuel pump in it about 8-9 months ago. I put an ignition module on it this evening with no change. I was doing some reading on the symptoms in a manual, it says the engine coolant sensor or the throttle position sensor. I don't see how those could affect it but anyway.. What do you think, throw a couple new sensors at it and hope or is there a way to test the injectors?

57 PSI MAY be a bit low, especially if your gauge happens to be a bit "off".

NO need to keep throwing $$$ parts at it... get a scan tool on it and SEE what info the throttle position sensor and the coolant temp sensor are feeding to the 'puter.

Does it NOT have spark? Or WHY did you replace the ignition module?

Have you tried squirting some gas into the intake through the open throttle butterfly with the air tubing disconnected? (Be SURE to get the squirt can of gas away from the vehicle to a safe place AND replace the air tube BEFORE trying to start it!!!!) Does it fire AT ALL?


(The CPFI "spider" fuel injection unit has 8 separate injectors bundled together with each pair of wires leading to the BIG connector separately and is UNLIKELY to fail completely so the engine won't even START.)

Also, take a look at the spark plugs. Is it POSSIBLE the engine "flooded" and fouled them... are they carboned and WET or clean and DRY?

ANOTHER thing you can try... with the ignition switched "OFF", disconnect the harness from the Mass Airflow Sensor, then try to start it. (A failed MAF sensor can prevent the engine from starting, with it disconnected the engine SHOULD start and it should run in "limp home mode" from computer-selected default fuelmap data.)

Another possibility would be a failed/slipped timing chain. You can verify the cam is turning by removing the distributor cap and seeing if the rotor turns while the engine is cranking. To verify that is hasn't "slipped time", there is a timing mark on the distributor body (marked "8") that must line up with the tip of the rotor when the engine is at #1 TDC with the line on the damper aligned with the notch in the timing tab on the plastic timing chain cover.

Post back after you check some of this stuff out!

if the TPS is stuck wide open it may go into Clear Flood mode , killing injector pulse . Will try to run if you spray gas or carb spray in intake ?

Here's the rest of the story. About two weeks ago, the truck wouldn't start. It didn't have any spark. I replaced the ignition module and the truck started and has run fine until a couple of days ago. I checked the spark this time, it has spark, but was kind of yellow instead of bright. Put in new plugs, now it has a bright white spark on all 8 cylinders. It shows about 10psi while cranking, but when I pull the plugs, they're dry. I poured a little gas in the TB, it will chug over 2-3 times and die. My scanner doesn't show any codes in the computer, that's why I'm kind of stumped of where to go next. Feel like I'm shooting in the dark now.

Are you saying fuel pressure drops to 10 PSI while cranking or WHAT does the 10 PSI in this latest post refer to???

If the pressure REALLY is dropping to 10 PSI while cranking, NO WAY will it start!

Could be clogged filter or pump problems or even a power or ground problem keeping the pump from getting full power.

Sorry for the short 10psi description. The 10psi is the oil pressure while it"s cranking.

(quoted from post at 04:37:06 03/07/11) Here's the rest of the story. About two weeks ago, the truck wouldn't start. It didn't have any spark. I replaced the ignition module and the truck started and has run fine until a couple of days ago. I checked the spark this time, it has spark, but was kind of yellow instead of bright. Put in new plugs, now it has a bright white spark on all 8 cylinders. It shows about 10psi while cranking, but when I pull the plugs, they're dry. I poured a little gas in the TB, it will chug over 2-3 times and die. My scanner doesn't show any codes in the computer, that's why I'm kind of stumped of where to go next. Feel like I'm shooting in the dark now.

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You need a HEI spark checker to confirm that you have enuff spark,,, get the real deal it will take the guess work out of it... then if it will pop the HEI spark checker move on to fuel pressure.... 55 PSI is border line,,, throws up a flag, means it needs a pump regardless of whether it fix's it are not... It must hold pressure when you turn off the switch also... PCM failers are not common but do happen,,, what I see when they fail is intermediate no starts that become more common... When they fail you loose battery/ignition voltage to the cam and crank sensor... Beware you will have some ghost voltage if this happens...

PCM's are not that expensive nor the flash job.... Confirm spark with the right tools,,, if you have spark but it will not fire a HEI tester I would condemn the coil/cap/rotor rite fast.... Aftermarket caps and rotors have been a BIG problem for me.... I have had them crap out in less than a week... You can thank China,,, low bidder got the contract... I replace the local NAPA owners cap and rotor at least once a year,,, its failed so many times he can tell the warn'n signs 8) Pays well also.... :lol: