No crank from ignition but will start by jumping the starter off the battery - engine RPM went through the roof

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Gormy

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Original poster
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Nov 8, 2023
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Wilmington, NC
Hey all,

I am in the end stages of a Jeep build. Long story short I bought a TJ that was mostly rusted away. Bought a frame from one guy, a body tub from another, and swapped my drivetrain and wiring into them. So essentially three Jeeps into one. I have a no bus issue (could be related). The fuel pump kicks in but there is no crank. All exterior lights work (unless I have the headlights on, then the left turn signal indicator in the instrument cluster stays on and I can't use my left signal). Radio works, HVAC works, everything works great.

New battery, new starter, new lots of stuff.

Go to start and there's nothing at all. Disconnected each harness from the PCM one at a time and cycle the ignition, no bus each time. Tried the smaller 5v sensors I found listed (crank pos, cam pos, TPS, etc) and disconnected each, plugged back in, no bus error still. Looked at the #12 fuse behind the glovebox and it's fine. Can only find two disconnected wire harnesses under the hood, one for the A/C which I removed and he other is back behind the fuel vacuum canister (can't find anything it goes to).

Said screw it and with the ignition off I jumped the starter from the battery and it cranks right over. Decided to turn the ignition on to get fuel to engine and jumped it again, fired right up. First time it has ran since last November. Sounded really good for the first 1.3 seconds before the RPMs shot WAY up. Ignition cable has full slack. Not sure why it did that. Is the throttle position sensor shot?

I don't know if the no bus error is a separate issue? I think I likely have an ignition issue if the starter can be jumped. The ignition worked when the Jeep was unloaded and I pulled it into my garage last fall. There was no no bus issue (but there was an issue with the left signal indicator staying stuck on). I'm really not shocked that I must not have reconnected something right, as I scratch built this from multiple Jeeps and essentially built it from an empty frame. Suspension, steering, clutch, flywheel, starter, plugs, wires, all fluids, new transfer case cable drive linkage, new brake lines and fuel lines, bumpers, all exterior lighting, fender flares... this thing is half brand new.

Does anyone know why I can't start it with the key, can jump it from the starter, and with the ignition on and all slack in the accelerator cable, it damn near grenaded itself by over-revving?

1999 TJ, 4.0L, 5 speed
 
That sounds like it might be a broken ignition actuator pin.


As for the revving, that's usually a massive vacuum leak. Have you had the intake/exh manifolds off?
 
JKP said:
That sounds like it might be a broken ignition actuator pin.


As for the revving, that's usually a massive vacuum leak. Have you had the intake/exh manifolds off?
Click to expand...

I was just out messing around with it some more after doing more reading. Two things to update:

I found two hoses disconnected. One was at the leak detection (hose fell out of the elbow). The other was at the T connection that runs across the firewall and attaches to the HVAC hose in the cab. I’m hoping that resolves the revving issue, but I’m not going to attempt starting it by jumping the starter again until I have someone here to kill it if it revs again.

Also, I’m not certain that it’s the ignition actuator pin. I see that’s a common issue, but when I slowly roll the key forward to try starting it, I can hear it click from the fuse panel behind the glovebox. I think the ignition is working properly or it wouldn’t be doing that, right? I swapped fuse 19 to 20 to bypass the clutch safety switch and it still won’t start. The next thing I want to test is power on the ignition wire to the starter, but I need someone here to turn the key while I watch the multimeter.

I had the intake and exhaust manifolds off but with new gaskets I think they’re on nice and tight again. Not sure if there’s anywhere that there’d be a leak coming from with them.
 
JKP said:
If the intake is not on the guide pins exactly right, it won't seal. Usually the cause of the high rev at start.

https://wranglertjforum.com/threads/how-to-drive-home-if-your-ignition-pin-actuator-breaks.10902/
Click to expand...

Thanks for the tips. I will double check the intake tomorrow. I think it’s seated on there perfectly but maybe it’s not. I’ll order the ignition parts for now. It won’t hurt to replace them as I’ll already be in there replacing the multifunction switch. Still seems like it’s working okay though if I can hear it clicking the relay behind the glove box.

I still can’t find the source of the no bus error. I’ve disconnected and reconnected nearly every harness I can get to. Will a no bus error prevent the engine from starting? Or is it a coincidence? It’s weird to me that the ignition worked fine when I shut it off in November and now the first time I try after fully rebuilding this Jeep, it doesn’t work. It seems like a different wire likely is the culprit.
 
I've had pins in my ODB connector corrode to dust...

I'm assuming you're getting no bus at that port?

Make sure you're gone through the wiring diagrams and checked every ground is connected.

When I frame and tub swapped my 97 I accidentally swapped a couple of the harness connectors under the steering wheel. Might want to check those are right and tight.


-Mac
 
macleanflood said:
I've had pins in my ODB connector corrode to dust...

I'm assuming you're getting no bus at that port?

Make sure you're gone through the wiring diagrams and checked every ground is connected.

When I frame and tub swapped my 97 I accidentally swapped a couple of the harness connectors under the steering wheel. Might want to check those are right and tight.


-Mac
Click to expand...

Hi Mac,

Thanks for the response. I haven't plugged a code reader in yet to the OBDII (can't find mine and don't want to buy a new one right now. From what I understand with a no bus error, you likely can't read any codes). I'm awful at reading wiring diagrams, but I have the main battery harness grounded to the firewall, the engine ground strapped to the hood, the additional ground strap from the passenger side of the engine to the frame rail, the four different grounds I could find on the dash (two on each side, one to the speaker mount and one to the body), and that's all I can recall. I'll run a search online for all the grounding locations and see what I come up with.

I don't recall that any of the wiring harnesses under the steering wheel are similar and can be accidently swapped, but I'll give them another look. They all seem to be different sizes.
 
Update: I do not believe it is the ignition switch or the pin/actuator. I took the ignition switch off and did not see a broken pin anywhere. Turned the ignition with a screwdriver, and it still won't turn on. It does the same thing as it does with the key: go to accessory and the fuel pump kicks in. Go to run and it clicks from the fuse panel behind the glovebox.
 
Gormy said:
I should have that attached too. I have at least four grounds connected inside the Jeep behind the dash.
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Did you ever figure out the issue? Im having the same issue where I can jump the starter but when I turn the key from inside it just turns on accessories and I bear a clicking from behind the dash.
 
AidenC said:
Did you ever figure out the issue? Im having the same issue where I can jump the starter but when I turn the key from inside it just turns on accessories and I bear a clicking from behind the dash.
Click to expand...

Hey! I did. I have another post that got very long (100+ replies I believe). To summarize, it was an issue with a ground wire that broke near the transmission, in combination with an intermittently working ignition switch.
 
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