Please help!!! No Starter Crank

[Boltrunner]

I have a 87 v20 4x4 350 3speed. It was a ranch truck untill i bought it back in October. It needed a fuel pump relay and a new pump. Got those things worked out and it runs great. Unfortunately just yesterday it would not crank. I could hear the pump prime but the starter wouldnt kick on. The wire under the dashboard is a mess. Ive narrowed it down to the fuse box area. But my knowledge of what should be there isnt that good. I dont know what should be there and what was hacked back together. Would someone please post a picture of what it should look like under the dash near the fuse panel. Also what are these? Today while under there i was able to end up getting the truck to crank but not fire. And the pump is not priming either. Im not sure what i did while i was under there besides shaking wires around

 

[chengny]

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Like this:

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[chengny]

First test for the non-start is simple:

Turn ignition switch to RUN and verify that the SES (service engine soon) warning is illuminated.

If no SES shows, the ECM is not functioning or is not powered up. If it is on, just do a standard non-start diagnostic. This is my method, use it at your own risk:

Check whether lack of fuel is the cause. Get a can of ether (AKA starting fluid), remove the air cleaner cover and spray a generous - but reasonable - blast of ether down the throttle body. Then quickly (before the ether can evaporate) hop in the cab and move the ignition switch to START.

If the engine fires right up - and then dies when the ether is gone...it is safe to assume that the non-start is due to lack of fuel flow.

If the engine doesn't even kick...pull a plug, ground it to the block, crank it over and observe for a healthy spark.

A healthy spark is a bright blue arc across the electrode gap that emits an audible snap. If you see a feeble yellow trickle of light across the gap - that is not a healthy spark.

Do those tests and provide the results. (It's almost sure to be a fuel related issue).

Next step is to override the fuel control system and force pump operation. Let us know what you find and someone will step-by-step you through that procedure.

BTW - if you don't have a multimeter, you need to get one - and learn how to use it (at least to test for continuity and low DC voltage).

 

[Boltrunner]

Well went out to start those tests as listed above. Truck does not crank now. Fml.

 

[1987 GMC Jimmy]

If you want, you can buy a remote starter and bypass the starter switch so you can run your tests.

 

[Boltrunner]

The truck was cranking when i originally posted. When this started the pump would kick on to prime but the truck wouldnt crank. Now i get nothing. I have checked my grounds and the ground wires for continuity. Ive checked the wires to the alternator as well. The grounds i have checked is battery to frame, battery to block, block to frame. I checked my power to the starter and that wire has continuity. Same with the battery to alternator. I do have a multimeter, test light and a continuity as well. Im pretty positive its in the rats nest near my fuse box. Thanks for the help everyone btw. Today its pretty crappy out so it will be full of studying diagrams and waiting for the great advice from everyone here

 

[Boltrunner]

On a side note. The purple wire on the pulse wiper module is cut. What specifically is that one for?

 

[chengny]

The truck was cranking when i originally posted. When this started the pump would kick on to prime but the truck wouldnt crank. Now i get nothing. I have checked my grounds and the ground wires for continuity. Ive checked the wires to the alternator as well. The grounds i have checked is battery to frame, battery to block, block to frame. I checked my power to the starter and that wire has continuity. Same with the battery to alternator. I do have a multimeter, test light and a continuity as well. Im pretty positive its in the rats nest near my fuse box. Thanks for the help everyone btw. Today its pretty crappy out so it will be full of studying diagrams and waiting for the great advice from everyone here

What I would do - when the weather gets better - is to find out why the starter isn't cranking. First check is to confirm that control power is making it from the ignition switch to the solenoid. Easy test - if you have a helper.

With an automatic transmission, when the key is in the START position, power from the ignition switch is supplied directly to the "S" terminal at the starter solenoid on a purple lead (if equipped with a manual transmission it must first pass through the clutch safety switch).

While you are under the truck (with your meter connected to the "S" terminal and ground) have the assistant try to crank the engine. You should see 12 VDC when he has the key in START.

If you don't get 12 volts at the purple wire/"S" terminal, try this - if you're up for it. It sounds drastic but really isn't, you'll simply be simulating what happens in the ignition switch when it's turned to START:

Have the helper turn the key back to OFF. Then you take a big old screwdriver (or some other tool you don't need to be perfect - because this test will cause some pitting) and use it to jump the "S" terminal to the "B" terminal. The B terminal should have 3 wires connected: One big black from the battery, and two medium reds that feed the truck's electrical system.

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At first, just jump the B to the S for a split second and see if the starter cranks. There will definitely be some sparks when you make and break the connection - so don't be surprised. If the engine cranks when you jump the solenoid, take the next step and try to start the engine:

Have the assistant move the key to RUN and then you re-establish the B to S connection. This time stay with it for awhile. Let it crank and see if the engine fires.

If it does fire up (and I doubt it will), that's good. But I'm sure you don't want to start the truck as above every time, so you'll have to ring out the starter control circuit. We'll cross that bridge when we come to it.

If you do see power at the "S" terminal when the helper turns the key, you can pack up your meter and start looking for a new starter.



BTW - are there any other electrical problems? Do the headlights work? How about the wipers, radio, HVAC blower, etc?

Here is one more test you can do that will help speed things up. If there is no power to the solenoid from the ignition switch, check for a burnt fusible link in that circuit's power feed. Locate the junction block on the firewall - it's shown below. Use your meter to test for 12 VDC at both points as indicated. (You will need to pierce the insulation with your probe to get a reading at point 2). Key position doesn't matter, those test points should always show battery voltage. Also you only need to test one of the leads coming out of the fusible link (point 2):

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I know this is a slow process, but it sucks trying to diagnose non-starts over the internet. Bear with me - we'll get it.

 

[chengny]

On a side note. The purple wire on the pulse wiper module is cut. What specifically is that one for?

The PPL lead supplies the ground path for the wiper motor's high speed windings.

 

[Boltrunner]

There are no wires go8ng to my clutch saftey switch. There is a yellow and purple wire twisted together under there though.

 

[Boltrunner]

Also my ses light is not comming on when the key is turned

 

[Boltrunner]

Checked power to the junction block under the hood. 1.6 volts at point one as indicated in the picture. 0 at point 2

 

[chengny]

There are no wires go8ng to my clutch saftey switch. There is a yellow and purple wire twisted together under there though.

Apparently, the CSS has been jumped out for some reason. It is now possible to crank your starter over with the engine/transmission mechanically coupled to the drivetrain (if the transmission is in gear). That's okay if you are aware of the situation - but a possible hazard to someone who isn't. Should be fixed.

 

[chengny]

Also my ses light is not comming on when the key is turned

This is a real problem. We can't proceed any further with diagnostics or repairs until you have a functioning ECM. Fortunately, this issue is probably a direct of the problem below and won't require a new ECM. Let's let it be for now - and see if it resolves itself after we have eliminated the apparent voltage drop between the battery and junction block.

 

[chengny]

Checked power to the junction block under the hood. 1.6 volts at point one as indicated in the picture. 0 at point 2

For this discussion, FW = firewall, JB = junction block, and FL = fusible link.

Below is a simplified - but accurate - dwg I made showing the primary power circuits (including the associated 3 fusible links) and what components they supply power to:

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The ECM power supply is from 3 sources:

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Two are from the ignition switch - and then to the ECM via the ECM1/GAUGE fuses. Those circuits are hot only when the key is in the RUN position.

The other power supply is direct from the battery - via the ECM B fuse. That circuit is always hot - it allows the ECM to retain certain settings and data even when the key is in the OFF position. Associated fuse positions:

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But that is all just background info. The hope is that there is nothing wrong with those circuits. The tests you did at the FW JB (on either side of the fusible link) determined that the problem is on the line side of the FW JB rather than on the load side (think of line side as inflow and load side as outflow).

The apparent drop from 1.6 to 0 volts across the FW FL is probably an anomaly - due to meter error or extremely low current capacity in the cable. The bottom line is that - no power is available on the line side of the FW JB. Consequently, there can be no power to the ECM...and no engine operation.

BTW - I changed the test point numbering system. Now, TP1 = line side of FL at solenoid, TP2 = stud on FW JB, TP3 = line side of FW JB FL

If you refer to the wiring diagram at the top of this post, you'll notice there are two more fusible links in the primary power supply wiring. They are physically located at the very end of the two red wires that are connected to the "B" terminal of the starter solenoid:

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One of those red wires feeds the headlights, horn and dome lighting circuits. It bypasses the FW JB and goes directly into the cab. - we aren't concerned with that one.

The other fused red wire is the one that terminates at the FW JB stud - where you got a 1.6 VDC reading. So, all that would indicate that the fusible link in that red lead (the one to the FW JB) is burnt - or nearly so. We have to determine which of the two FL's is the affected one and repair it.

A fusible link is simply a section of wire that has a cross sectional diameter that is 4 times less than the diameter of the wiring leading to the circuit it protects. In the event of excessive current flow, the idea is that the smaller diameter wire will burn up and open the circuit before the rest of the wiring can be damaged. A brief tutorial on FL's:

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Since the fusible links are mostly in that piece of metal conduit above the starter, they will have to be withdrawn from it in order to make the repair. And - also to determine which is the one we want to work on.

I think there is usually enough slack in the wiring that they can be released from the "B" terminal and pulled out of the pipe far enough to cut the failed section off and splice on a new one. You can the link at any parts store. I just checked and the correct diameter of the link is 14AWG:

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Here is the factory diagnostic procedure for NO SES:

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