No fuel when starting, injectors wont fire fully


#1

95 Chev G30 Van 5.7L, TBI. being a mechanic im stumped. the engine will run if i prime the TBI. no codes are being set. r&r the ingnition module, fuel filter. tested fuel pressure, 18 lbs. changed out ecm but used origional prom. pined outwires related to fuel, ignition and injector systems.

now trany wont shift corectly. this van was rebuilt 9 mo ago and has run fine untill now. any susguestions ?


#2

[b]If you’re able to keep the engine running by introducing fuel down the throttle body, it has to be a fuel delivery problem. The fuel pressure is within spec, so that’s not the problem.

Either the fuel injector is defective or the injector isn’t receiving a signal. You should be able to see the injector spray fuel down the throttle body as the engine is cranked. If not, then the injector and harness should be tested.

The injector harness can be tested for a signal with an inexpensive noid light. Most parts stores sell these. The injector can be tested by using an injector tester. But this tool costs quite a bit more.

But those are the areas I would focus on.

Tester[/b]


#3

once the engine fires up all engine systems run fine on there own. I just cant start it. tomorrow after church i will rent a “noid light” from the parts store to see if it is getting sin when cranking. also there is the trany shift issue and i think they may be related.


#4

The noid light will show (by flashing) if the injector (two?) is getting firing commands: but, it won’t show how LONG the command signal is (from the ecm [engine control module (“the computer”)]. How long the pulse is determines how much fuel the fuel injector injects. The auto parts store may rent/lend you a fuel injection pulse counter. The ecm needs the signal from the vss (vehicle speed sensor) to shift properly. The vss generates its signal when the vehicle is moving; or, the drive wheel raised, in gear, engine running. As a test, unplug the fuse to the egr valve. If the egr valve is being commanded OPEN, pulling its fuse will let it close.


#5

[b]OK! One other thing to check. Make sure the engine didn’t jump a timimg chain.

If a timing chain jumps a tooth or two, It can be hard to start. That’s because there’s cranking cylinder pressure and a running cylinder pressure. So if the valve timing is off, it can be hard to start, but runs once the RPM’s are up. Running compression.

And if I’m not mistaken, I believe that the teeth for the cam gear is made from plastic on your vehicle. If you find this to be true, another focus point!

Tester[/b]


#6

The schematic shows a 15 amp fuse powering the injectors and grounds being provided through the ECM. This fuse is also referred to as a “trans fuse”. Maybe?


#7

checked all the fuses. tested ok. probed injector for 12V at crank - ok.


#8

We know that the engine control computer (ecm) listens to the sensors which give it information on the engine. The sensors tell the computer: the gas pedal position (tps); the engine coolant temperature (ect); the rotating position of the crankshaft and/or camshaft (cps); the air temperature(iat (mat), and the air pressure (map) or mass (maf); and what the air to fuel ratio is (on hot engine) from the oxygen(O2) sensor. +++ Which sensor(s) does it listen to more during start? According to www.autozone.com Vehicle Repair Guide, those sensors are: the ect, tps, and cps. On later models, also, the map and iat(mat). My guess is the ect is giving the ecm the wrong temperature. +++ Using the pinout chart, take a voltage reading of ALL the pins. Turn the key off, and disconnect the battery, and take resistance reading from EVERY pin on the disconnected ecm connectors (A, B, C, D). This will yield the resistance through (almost) every sensor and actuator. The vss will be about 500 ohms, and the tps, map, iat (mat), cts will be several thousand ohms. If a value is found which is out of specification, you can go to that component for a closer examination. RECORD every one. +++ alldata.com has the Diagnostic Charts which list (among other problems) “engine won’t start”. It gives you step-by-step checks you can do with a multimeter. +++ The fuel injector DOES NOT operate on a steady 12 volts. The ecm chops the voltage into tiny pieces (pulses) to control the open time of the fuel injector. +++ The Haynes or Chilton’s manual is a good source of sensor testing information. +++++ A quick answer? Change the ect. It’s cheap.


#9

Well it has been a long haul to get it running. the ECM was shot by an electrical storm. replaced ecm,o2,oil pres sw, vcc, tis,tps, dis mod, and it is now running but no OD. last code to resolve is DTC 85