1988 Chevrolet S-10 getting to much fuel

Tiny
RAYMOND FOOS
  • MEMBER
  • 1988 CHEVROLET S-10
  • 2.5L
  • 4 CYL
  • 2WD
  • MANUAL
  • 250,000 MILES
Ok my truck caught fire about a month ago so I replace plugs and wires distrib cap, rotar fuel pump fuel filter and I also fixed burnt wiring got it started ran very good for a week then just died lost all power towed truck home there were no fire so I replaced plugs and wires again got fire then no fuel. I also replaced ignition control modular the computer the injector still no fuel I also replaced throttle control sensor tempature coolant sensor mapping sensor still wont start ok then it will start if you pour lil gas in throttle body then dies ok now found out the ground on connector was not spraying fuel into throttle body so I reran ground wire from injector to metal surface now getting to much fuel it keeps flooding out and dies im confused now
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Friday, September 26th, 2014 AT 1:39 PM

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Tiny
CARADIODOC
  • EXPERT
I'm confused too but I can share a few observations. You said you got spark back by replacing the spark plugs and wires, but that can't be. You know they didn't all fail at once. It's more likely you disturbed a bad connection or grounded wire someplace.

Fuel injectors have 12 volts applied to one terminal, usually only during engine rotation, meaning cranking or running, but not when just sitting there with the ignition switch turned on. The other terminal is pulsed to ground to turn the injector on, and the length of that pulse determines how much fuel goes into the engine. It sounds like you used a separate wire to create a solid ground, so the injector is going to stay turned on constantly and way too much fuel will be sprayed.

When you're missing injector pulses and spark, look for what both systems have in common, and that's the crankshaft position sensor and the camshaft position sensor.

Also be aware, for future reference, that if you're missing just fuel pressure, there has been a huge problem on those trucks with metal gas tanks. The ground is lost due to rust, and the stalling or no-start may be intermittent. To solve that, drill a hole in the flange outside of the weld bead, run a screw in there to attach a new ground wire, then attach the other end to the body or frame.
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Friday, September 26th, 2014 AT 4:15 PM
Tiny
RAYMOND FOOS
  • MEMBER
Thank you it does make sense and yes I did use separate wire for ground so maybe I missed a ground wire where ive spliced the burnt wires possibly but when I hook upthe connector to injector I get no fuel
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Friday, September 26th, 2014 AT 4:29 PM
Tiny
CARADIODOC
  • EXPERT
You gotta have 12 volts too to the injector. I'm not familiar with your specific engine, but I can share how 99 percent of these systems work.

12 volts to run the injectors, ignition coil(s), and fuel pump or pump relay comes from a main relay. Chrysler calls that the automatic shutdown (ASD) relay. It can also be called the fuel injection relay, ignition relay, or something like that. The Engine Computer turns that relay on when it sees engine rotation, (cranking or running), and it knows that by the pulses it gets from the crankshaft position sensor and the camshaft position sensor, (which could be inside the distributor.

This is done for safety reasons. If a fuel line gets ruptured in a crash, the fuel pump would dump raw fuel onto the ground creating a serious fire hazard. With a leaking fuel line there can't be any fuel pressure. With no pressure, the engine can't run. With a stalled engine, there's no pulses from those two sensors, so the computer turns the relay off which turns off the fuel pump, along with other circuits.

That means you have to check for the 12 volts feeding an injector while cranking the engine. Chrysler also turns the ASD relay on for one second after turning on the ignition switch, and before you crank the engine, to insure fuel pressure is up for starting. A lot of GM models turned the pump on with a tap on the oil pressure sending unit. It was the same principle. If the engine stalled, there would be no oil pressure so the fuel pump would turn off.

Getting that 12 volts to the injector is the first half of the story. Next, the computer turns the ground wire on and off to pulse the injector. The amount of time of each pulse is very precisely controlled and adjusted. I've never actually examined the "duty cycle", but as a guess, I'd suggest 30 percent is normal. That means the injector is pulsed on for 30 percent of the time, and off for 70 percent. Your ground wire is holding it on for 100 percent of the time.

If you have spark, the cam and crank sensors should be working, but this is where there can be major differences in how the systems work. Most engines will have no spark or injector pulses if the signal is missing from either sensor. Some engines will continue to run on one sensor when the other one fails, but it won't or may not restart after the engine is stopped. Some engines will run with one failed sensor but at reduced power.
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Friday, September 26th, 2014 AT 4:57 PM

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