1988 Chevy Truck Fuel injectors don't spray

Tiny
BRADSURFING
  • 1988 CHEVROLET TRUCK

Electrical problem
1988 Chevy Truck V8 Two Wheel Drive Automatic 165000 miles

I have been having trouble with a friend's vehicle he needs for work. It had a bad fuel pump, so dropped the tank and replaced it thinking it would fix the no fuel problem.
Getting proper fuel pressure at the TBi assembly. Motor fires over with starter fluid. Heard on this site http://www.chevroletforum.com/m_13174/mpage_2/tm.htm#63237 about changing the ignition module/pickup coil in the distributor to get the ecm to ground the fuel injector circuit.. changed out for a jy distributor assembly. Still no go.
Checked for voltage at injectors, 12v, and at the ECM's power out for them (A6 pin) 12v, and D14 and D16 I get 12v, so wiring is fine. After this in the circuit the computer grounds out the circuit, making it closed briefly and the fuel injectors fire.

Are there any other sensors/modules, when bad, will keep the ecm from grounding out the fuel injector circuit(s)? I haven't checked them with a noid light but pretty certain there isn't a circuit complete due to a bad sensor

attached wiring diagram schematic

also check the thread on page 2 I posted more info about the ignition module voltage at ignition on position, there was basically no voltage coming back to the ecm, but power in from the ignition coil to the module.

possible bad jy distributor? Any help appreciated, thanks!


http://www.2carpros.com/forum/automotive_pictures/173092_0900823d80087955_1.jpg

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Thursday, March 27th, 2008 AT 9:45 PM

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Tiny
BMRFIXIT
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You need to check the TPS volts
make sure its not in a flood mode
if its in flood mode ECM will not fire the injector
so check the volts at the TPS and also give it a good look
check if its moving with the paddle
good luck

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Thursday, March 27th, 2008 AT 9:55 PM
Tiny
BRADSURFING
  • MEMBER

Btw all fuses are fine (inj a + b, etc) and the ecu when tested gives 12 codes repeatedly when I jump the aldl connector

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Thursday, March 27th, 2008 AT 9:55 PM
Tiny
BMRFIXIT
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Disconnect the tps and check if you dont have a way to test the volts
that will put the ECM in a limp mode

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Thursday, March 27th, 2008 AT 9:59 PM
Tiny
BRADSURFING
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Flood mode voltage would be 5v meaning maxed on that circuit meaning the tps isn't doing the proper resistance potentiometer it should be? Or do I have it backwards (maybe cause I work on Fords heh) btw here's a better diagram the other one I attached thru the site didn't show up right:

so C13 blue wire should be power to tps, 5v, and the black wire should be the changed voltage so at closed throttle it would be 1v'ish back once it goes thru the coolant temp sensor that alters a bit too?

How does this go, thanks for any help here and for the help you've shown, it sound's like a possible bad tps

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Thursday, March 27th, 2008 AT 10:07 PM
Tiny
BRADSURFING
  • MEMBER

Forgot to mention I have tried to put it in limp mode before by disconnecting the TPS plug on the otherside of the TBi opposite of the linkage and still no fire from injectors. But I think I had disconnected the MAP sensor at the same time but I don't think it should've had bearing on the injectors spraying.

Maybe I need to check the ignition module once more.

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Thursday, March 27th, 2008 AT 10:10 PM
Tiny
BMRFIXIT
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If you can use a scanned it will be a plus
Tps is at the throttle body
flood mode will not allow injector to open unplug the injector and check it for pulse
ive seen it where the metal round that the air cleaner sits on cuts the injector wires you may wants to check that too
if wire good and TPS
far to do it but check the coolant sensor too
if all ok you may be dealing with a bad ECM

(flood 5 volts yes or over 3)

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Thursday, March 27th, 2008 AT 10:30 PM
Tiny
BRADSURFING
  • MEMBER

Bmr thanks for all the help. Just got back to it since i've been off-on'ing this for a friend

checked tps voltage at the ecu pins and at idle it's.5ish v and it goes up to 4.5 or 4.8 I cant remember when I pushed on the throttle pedal so I know tps is good

swapped the ecu's and didnt do it. Possibly wrong ecu
gonna get the old ecu reflashed either tonight or tomorrow night (no charge, good to know old employees :)

i did test the old ignition module and it had a bad reference signal (the last test on the diagnostic machine)
tested the newer one and it passed all tests

also checked the ohms for the pickup coil and it is where it should be (800-1300ohms not magnified)

spin the shaft on the distributor manually, set to volt AC and it's where it should be (.2 to.7 volt ac)

so the new distributor setup is good and not causing the ecu to cutout the grounding part of the fuel injector circuit

anything else you think might be the culprit? I've pretty much covered everything I think

is there a wire that comes off the fuel pump to the ecu that tells the ecu the fuel pump is on and/or primed? I havent checked but I did have to repair the ground wire for hte fuel pump (it works fine just fixed the connector on top the tank, soldered it up then taped)

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Thursday, April 10th, 2008 AT 7:50 PM
Tiny
BMRFIXIT
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All i add is check the wiring
check for battery power at the injectors with key on
and also check the wiring back to the ECM
let me know


http://www.2carpros.com/forum/automotive_pictures/99387_injector_1.jpg

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Thursday, April 10th, 2008 AT 9:14 PM
Tiny
BRADSURFING
  • MEMBER

I did this a while ago, probably didnt catch it due to all the info I gave
it's fine it gets power (oh that diagram where it has D4 for inj should be D14 btw cause d4 is really for ign module) it's a typo on chilton's behalf (where autozone gets the diagram)

i'll let you know how the reflashed ecu does thanks for the help

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Friday, April 11th, 2008 AT 3:46 AM
Tiny
STRTRCR405
  • MEMBER

Ok went through all the steps you listed and then some, still no luck with my 88 c1500, after a frustrating day of messing with it a buddy comes over taps on the injector a couple times and what do you know spraying like a champ and it starts right up! Might be worth a shot! Good luck

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Tuesday, February 22nd, 2011 AT 11:49 PM
Tiny
LONGO82
  • MEMBER

I'm having similar problems my truck is on the side of the road need to get it off have fuel going threw the line pump kicks on and all nothing coming out of the injectors however I was driving it pretty hard and then it just shut off idk if the process is the same as yours or not if I disconnect the tps will my Injectors fire?

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Tuesday, April 18th, 2017 AT 6:07 AM
Tiny
CARADIODOC
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You need to start a new question, and PLEASE list the engine size. This was an old private conversation between two people and is now listed as having received a reply. None of the other experts are going to see your addition of have a chance to reply. That won't get you the help you need. Also, some of the comments could be wrong if taken out of context, and will not apply to other engines.

In particular, the observation about tapping on the injectors doesn't sound right. There's two of them, and failure of one would be rare. To have both stop working at the same time is not very likely. A better suspect is spread terminals in the connector, but that usually causes intermittent operation of just one of the injectors. Tapping on that connector could overcome the bad connection and start that injector working, ... For a while.

You need to check for spark first, before you go looking for the hard stuff. The "clear flood" mode had better not prevent spark from occurring, as that would just make the problem worse. There was some confusion there to. The throttle position sensor on almost every engine has a 5.0-volt feed wire and a ground wire that will actually have 0.2 volts on it. The TPS has mechanical stops inside it that, for the sake of explaining theory, limits its range of travel on the signal wire from 0.5 volts to 4.5 volts. It is physically impossible for the signal voltage to go outside that range unless there is a break in a wire or a broken connection inside the sensor. Those wiring defects will send the signal voltage to 0.0 volts or 5.0 volts, and that is what the Engine Computer needs to see to set a diagnostic fault code. In actual practice, you may find the range to go from, ... Oh, ... 0.38 volts to perhaps 4.2 volts. No two sensors are ever exactly the same. The point is you must never see 0.0 or 5.0 volts on the signal wire.

Also understand that disconnecting the TPS may not prove anything. The open circuit on the signal wire will force an intentional 5.0 volts which is intended to set a fault code, and that code tells the computer to stop basing any fuel metering or other decisions on those readings. The TPS actually has the least say in fuel metering than any of the sensors. Also, nothing related to the TPS will cause loss of spark.

It's important to check for spark when you have no injector pulses. Too many people get hung up on the first thing they find missing, and neglect to see all the other related symptoms. About 95 percent of crank / no-starts are the result of no spark AND no injector pulses. The other five percent are caused by loss of spark, OR loss of injector pulses, OR a non-running fuel pump.

The coolant temperature sensor has absolutely nothing to do with the TPS or with modifying the TPS's signal voltage, except that multiple sensors share a common ground wire.

The place to start the diagnosis is always to first read and record the diagnostic fault codes. You can only do that yourself on Chrysler products, or on GM products older than '96 models. It's possible to read them on '95 and older Fords too, but it's a miserable procedure and takes a long time. For '96 and newer GMs, you need a scanner or a simple code reader. Those fault codes may tell you the circuit or system that needs to be diagnosed, and for this problem, that is most often the crankshaft position sensor circuit or the camshaft position sensor circuit.

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Tuesday, April 18th, 2017 AT 8:16 PM

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