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Ivan, ASE Certified Master Technician
Category: Chevy
Satisfied Customers: 4871
Experience:  ASE Master Tech. 20+ years experience. 9 years self employed. Expert on AUTOLAB Radio Show
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chevy cheyenne: what makes a chevy crank but not start?

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what makes a chevy crank but not start?
Hello and good evening. The 3 things that will keep an engine from starting is fuel, spark, and compression. Let's find out what we are missing. I would like you to spray some carburetor cleaner into the throttle body and see if the engine sounds different. Like it tries to start. Something other than the way it sounded before. If it does, we know the problem is fuel delivery and not spark. If it doesn't we need to focus on spark . Let me know what happens.

Your JA Expert,
Customer: replied 3 years ago.

we have put gas down in it and it fired up so theres no need for this test. i have like-new plugs wires and distributor rotor bug.


Ok, so spark is good but we do not have fuel injector pulse or fuel pressure. Our next test then is to check for fuel injector pulse. If you have fuel pressure and no fuel injector pulse, fuel will not pass through the injectors. Remove the electrical connector for the fuel injector. With the key on, you should find power on one terminal of the connector. Use a NOID light or a LED bulb and place it across the two terminals of the connector. With the engine cranking, you are looking for that light to flash very quickly. That will confirm power and the computer grounding the injector to pass fuel. Let's make sure the computer is trying to pulse the injector. Try this and let me know what happens.
Customer: replied 3 years ago.

the test light stays on no flash.. what the prob doc? where is my computer ground located


The flash won't happen unless the test light has a Led bulb. Things however look like an ignition module. Does the test light have a bulb or Led?
Customer: replied 3 years ago.

a bulb. and i grounded on battery and put other end on the hot wire on one injector. i did happen to buy an ignition module today but didn't replace it yet... could it be? im not trying to waste any more money then i have to (of course). also.(more info) when i tried to get a computer diagnosis (before it died out) the computer operator couldn't get grounded, like a month ago.


Throw that module in and see if that puts you back in business. The problem with a bulb over a LED, is that the bulb cannot flash fast enough to show you pulse. A LED can. The signal for the computer to see RPM come from the ignition module. You can have injector pulse and not have the signal to the ECM for RPM. Spark does not go through the ECM. Since you have the module, put it in and let me know what happens.
Customer: replied 3 years ago.

the fuel pump is unchanged. still don't kick on when i turn the key.


That is with the ignition module installed?
Customer: replied 3 years ago.

yes sir.


Ok, we really need to see what is happening at the injector for a better picture. If we have good strong flashing, then we know if sufficient fuel was present, the injector should pass it. If we do have good strong flashing, we now look at the items that cause and allow the fuel pump to operate. If we have flashing but it is dim or slow, we are looking at temperature related controls like coolant temp sensors that may cause the injector to have a much smaller pulse width which would not pass enough fuel through the injector. If we have no injector pulse, meaning no flashing, we now have only a couple of reasons, 1. The ignition module, 2. the ECM itself and the powers and grounds that supply it, and 3. the throttle positioning sensor that will cause a wide open throttle signal that becomes Clear Flood mode when the vehicle is not running. This shuts the injectors off to allow a flooded condition to clear. These are the areas we are focusing. A NOID light is the best device and inexpensive if you can buy a single one for your style injector. If you want to go cheaper, go to radio shack and buy a 12 volt capable LED bulb. Run jumpers into the 2 terminals of the unplugged connector. There should be no ground until you crank the engine. Then if the computer is grounding the injector, you should get very fast bright flashing. A bulb will just stay lit because it doesn't have enough time to turn on and off fast enough. Pursue this path and we can truly figure out what we are dealing with.
Customer: replied 3 years ago.

how do I get back to this answering service tomorrow without paying twice for my final answer? I am going to have to go buy an led light.


You just reply to the link for this question. That will bring you back to me and our discussion. Your initial outlay is a deposit, you will not officially pay until you are satisfied with our service. Just post back to me when you are ready. I will respond as soon as I see it. Have a great night. This is an example of a Noid light set, just so you know. You may be able to find a single one. I figure I would show you what I was talking about.
Customer: replied 3 years ago.

okay, so I went this morning and got a Led test light/probe, and it has power to the connector from the battery to the wire, but there was no initial blink,.. when connected to the separate connectors on the injector inlet, there was no power what so ever. .


I'm rolling in traffic, I'll respond when I get out of the car.
Customer: replied 3 years ago.

thank you 17 year Gm tech is trying now but I think id rather listen to you. you give better detail, when parked ill tell you where we are in the conversation.


Customer: replied 3 years ago.

17 year gm tech says he has the wrong wiring diagram and he is afraid he cant help me.


Customer: replied 3 years ago.

are you online?


Very shortly, I'm still responding via my phone.
Customer: replied 3 years ago.

how do you send a message before its even that time? lol are you there im still broke down.......


I am here now, sorry about the delay. I was traveling.
Customer: replied 3 years ago.

it is fine. understandable. what can you tell me?


Ok so just to bring me up to speed. Power is present on one wire of the connector, and when you put the LED bulb across the two terminals of the unplugged connector it does not flash or light when you crank the engine. Does that sound accurate?
Customer: replied 3 years ago.

yes sir. there is no pulsing ground, fuel is getting all the way up to my TB but no injection is taking place. also my fuel pump doesn't kick on when I turn the key. diagnosis?


Ok, on the Throttle Positioning sensor, there are 3 wires. One is ground, one is 5 volts and the middle wire is the signal back to the computer. With the sensor connected, tell me the voltage on that signal wire. If it is too high, the computer will shut off the injectors. That is our next test.
Customer: replied 3 years ago.

so I can locate it easier where would that be located?


If you are looking at the throttlebody, the throttle linkage will connect to one side. Directly on the other side of the throttlebody from the pivot where the linkage attaches, you will find the throttle positioning sensor. If you need a picture, I can get you one. It will not be hard to spot. It measures how far the throttle plates open, so the pivot of the throttle plates go directly into it.
Customer: replied 3 years ago.

so ill go test the middle signal wire I found it be right back. gatta plug back in my ecm?


Yes, plug in the ecm and check all 3 wires. Make sure 5 volts is on one. The middle wire should be about .50 volts. Here is a picture.


Customer: replied 3 years ago.

where should I ground to check those three wires on the plug? I don't think im getting anything.. grounded on battery, and on the remainder connectors also... but im not getting anything but a (-) sign in front of .00


Any metallic surface is good. The key has to be on and the ECM needs to be plugged in. You want DC voltage on your meter and the sensor should be plugged in. You want to backprobe the wires. A straight pin works good for piercing the insulation.
Customer: replied 3 years ago.

I still get no juice.


Does the check engine light illuminate when you turn the key on
Customer: replied 3 years ago.

every once in awhile... when it drove. comes on goes off now. check gauges stays on now. and I wasn't able to get a diagnosis at oreillys.

If you turn the key on right now so the gauges register is the check engine light on?
Customer: replied 3 years ago.


it is not.

Great! We now know what is going on. The ECM is not powered up. Look for a blown ECM fuse. Check all you fuses and make sure if it has power on one side it has it on the other side of the fuse. Do this with the key on.
Customer: replied 3 years ago.

check fuses with a fuse checker? and both sides? elaborate please.

Use your test light. On each fuse, there is a little metal tab on the top of the fuse that you can touch with the tip of the test light. With the key on, and your test light grounded at the clip, touch to each of those metal tabs. You don't have to remove the fuse. If power shows up on one side of the fuse, it must be on the other side of the fuse at those metal tabs. If not, the fuse is blown.
Customer: replied 3 years ago.

man. I just heard her bust off... and purrrrrrrrrr 100% my man! thank you very kindly for your time and services!!!!!!!! happy customer!!!! tell your boss I said you know what the f**k you are talking about and to give you a frickin raise! I will gladly pay my one time fee now.. I cant explain to you how much I appreciate your skill of knowledge. THANK YOU VERY MUCH. !

Awesome! You are very welcome! Most likely the fuel pump had failed and killed the fuse. Enjoy the ride!

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