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fuel injection rejection

wheels87k5

wheels87k5

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87 K5 w/tbi.....truck will start fine...and idle fine...when you give it a little throttle, it boggles down and wants to die...also wants to die if put in gear. Passenger side fuel injector has a cone shape spray, driver side does not...If I swap electrical connections, driver side injector has cone spray, passenger side does not. I used a timing light to get a good view of the cone spray. What the heck is going on...both fuel injectors are new...so is fuel pump and fuel filter.?
 
Does anyone have a clue to this problem?....is there a voltage issue with the seloniods?
 
you've already found what it's NOT. injectors are fine, apparently. simplest answer is a bad wire or connection to one injector. check the voltage on the suspect pod.
 
I checked the wires for continuity...they're good...do you check the voltage while running and what should voltage be?....I was told it could be a timing problem...but timing has been checked. If voltage is an issue, what causes the difference? thanks
 
You can put a noid light on the injector connector and see if it lights up similarly on both when cranking. Bad ground, weak bulb. Voltage is somewhat meaningless, as the ECM *grounds* the injector wires.

Not knowing the TBI wiring myself, are the injectors on one or two fuses?
 
what is a noid light...i'm new at this tbi stuff....have replaced about everything except the engine;) It does have the heavy exhaust smell and light smoke from the tailpipe (sometimes). will timing do this?
 
Timing will not affect only one injector. :) You are seeing a physical problem that needs cured. If it's not spraying right, it's likely not burning right either, which would cause symptoms you describe.

Noid light is simply a 12V lightbulb with wires on it that when connected to a 12V source and ground, lights up. You can use a taillight or dash lightbulb, just connect wires to it correctly, and strip the ends of the wires.

Digital multimeters do not respond fas enough to give you an accurate picture of what is going on. Analog meters are faster, but I don't own one, so no idea if they are fast enough to show you how strong the "injection pulse" is.
 
Ok....on one injector is a green and white connector, on the other is a blue and red connector...do you hook one side of the noid to the green side and the other side of the noid to the white side, then crank the engine? what am I looking for?
 
You test each connector seperately. In your example, green and white would be tested (one wire to each) then blue and red.

Looking to see what happens when you crank it on either one. You *should* see a difference in the light as it turns over, the one with the weak spray pattern being dimmer. That would mean you've confirmed a ground problem, as you know you are getting enough voltage to the injectors.
 
What causes a ground problem if that is the case? This K5 was supposed to be a daily driver when I bought it, but it turned out to be a lemon...I'm not giving up on it...it's mine and will be a great 4x4 when I can get it to run...I've already spent more than $1700 in new parts because of the unknown milage...sooner or later we'll get it right.:D Thanks for all the help from everyone. :bow: Wheels
 
Could be bad wiring, poor ground in the engine harness (unlikely because the grounds should all be tied together, and would exhibit same symptom on both injectors) or the ECM. I'm sure there are other wacky things that could cause this problem, but with the ECM grounding the injectors, and you haveing correct voltage in, I can't think of anything more likely.
 
What puzzles me is it starts up with no problem, and will idle pretty good...there is a very slight surge but very small...sometimes no surge at all...when I look at it with the timing light, you can see the cone shape spray when you give it lots of throttle on one injector but not the other...I thought it was opposite when I switch the connectors but was proved wrong when I noticed it really didnt matter all the time...sometimes you see the cone on one or the other...but not both. If you give it light throttle, it starts to boggle, then give it lots of throttle and it idles fine. (scratching my head and loosing more hair):confused: I'll do the noid test after work tomorrow and see what happens. Thanks again.
 
Couldn't wait...made a noid light and hooked it up....the lightbulb didn't light up at all when cranking the engine...is this a grounding problem? if so, what to look for?
 
Make sure your noid light works (battery terminals are good tests) as if the engine starts, the light HAS to pulse.

And to emphasize, since there is obviously something wrong in the testing procedure/equipment, you test *one* injector connector at a time, one wire from the bulb going to one terminal of the connector, the other wire to the other terminal.
 
Yes...I did make sure the noid worked by using the battery...I needed to make sure my soldering was good also....I connected the light to one set of injector wires, cranked the motor and the light never lit up...period...no pulse...nothing...as long as polarity doesn't matter.
 
Polarity doesn't matter.

You left one injector connected while you tested the other connector? That could matter, depending on how it's wired.
 
I connected one injector, put the noid on the wires to the other injector, cranked the motor, motor started, noid light did nothing while motor running.
 
Got an analog meter?

Don't know what to tell you, light has to flash if the noid light is working and the circuit is being grounded by the ECM. Apparently it is, the engine runs. :)

You can check for continuity to ground on the injector wires, since the ECM is supposed to ground them, with the engine off, there should be no continuity.
 
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I am going to ask the age old question....Have you checked for trouble codes? Does the CEL light up when key is turned on?
I am going to go in a diferent direction from the injectors. Your problem may not be in the injector circut. You may have a bad dist module or magnetic pick up coil. A intermittent short may be causing the ECM to shut off the injectors.Then when it sees spark again it will let them fire.
Check all connections and grounds for the injectors and ignition circuts.. Check the pulgs on the ECM to make sure everything is plugged in tight.
 
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