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99 4X4 2.7L 5 Speed Manual, Hi Guys, I'm new to this Forum Thing, So Please be patient with a Newbe. This Taco was running fine until last week when The Son ran it out of gas. From there, couldn't get it to pick fuel back up. Fuel Pump gone, right? Replaced it and now it cranks only when it wants to. So, I plugged my ElmScan5 Up to see what might be going on. :nerd Imagine my Surprise, :surprise, the Scanner won't connect. Been a while since I used the tool, so I updated the software. From there I was able to get it to link up and scan, and what do U know, no codes set. Cleared parameters and code memory anyway, already here there. Next, turned the switch to try and crank just to see. Viola, it cranks up and runs strong! After checking O2 sensors and all else, I disconnect and shut her off. Unplug Scanner and button everything up. Now for a test drive, turn the key, no start. I have spark, fuel and and compression, so why won't it start? i know that it's in time, cause when she runs, she roars! Been seeing several threads on these Forums about others having issue with the MAF sensor. So I checked that, all is up to specs. could it be that the ECU has a bad ground and the Scanner is giving it an alternate route? Any and all Help from U Motorheads out there are Welcome. They say that 2 heads are better than 1, so what can we accomplish by putting all of ours together? Thanx Dogg:brickknoc
 

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Mambeau / Admin
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Moving thread out of Build section (where no one can reply to it ...).
 

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99 4X4 2.7L 5 Speed Manual, could it be that the ECU has a bad ground and the Scanner is giving it an alternate route?

The ECU ground is located in the engine compartment under the throttle body (brown wires bolted to manifold I believe). You can check that for looseness
 

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Thanx Enola, was a bit flustered and tired when I initially posted. didn't realize I was in the wrong section. Now because of your quick action, maybe I can get some responses.
 

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Mambeau / Admin
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The ECM grounding issue would explain everything, but it's not the only thing that might have happened.

(1) With the scanner disconnected, does the starter turn when you work the ignition switch, or is it totally 'dead' (no starter action at all)?

(2) If I'm not mistaken, the ECM has to be getting a signal from the crankshaft position sensor before it (the ECM) will activate the Circuit Opening Relay. My point is that a crank position sensor problem might explain it, though it should have thrown a code. If the ECM was faked into thinking it was in test mode with a scanner attached, that might explain why it only fires up with the scanner attached. It might also explain why no codes are being stored.

(3) There's always the outside chance something's shorted or open in the DLC3 connector itself (e.g., a pin got bent while attaching the scanner).
 

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Discussion Starter #6
Sorry It has taken me so long to respond to your input on my thread. But, we run a Tanning/Storage Business here, and with my son getting a job driving Semi Trucks over the road, the Taco sort of got pushed to the back burner. The engine does turn over when cranked, just doesn't want to crank. Also, another odd thing I have noticed, after reading another thread and trying it. Sometimes, If you crank the engine over long enough, it will eventually crank. I read something in another thread about the IAC Valve being stopped up, and unable to close. Thus allowing too much air into the intake during initial start up. So, I have tried Cranking longer and/or spraying a bit of ether into the mix. Both have worked some of the time, but not consistently. The ONE Thing that works every time, is attaching the ELM Scan Tool. It always Starts when there is Communication between the Tool and the ECM. Also, I checked for bent pins in the OBD Connector and found none. Thanx for the Interest Enola Gaia
 

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Mambeau / Admin
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(1) Here (attached) is the 1999 3RZ engine control wiring diagram.

(2) Look under the driver seat / carpet for the BN1 connector and double check that all pin connections are tight. Your fuel pump grounds through the BN1 connector.

(3) The fuel pump grounds to ground point IG (up behind the dash; near the left / driver side end of the structural support). Your DLC3 connector connects to 2 ground points - one of which is the IE point behind the dash near the _right_ end of the structural reinforcement piece. The other ground connected to the DLC3 connector goes to ground point EB (the one near the throttle body).

Double check all 3 grounds (lines and end points). If plugging in the scanner makes everything OK, I suspect connecting the scanner is completing an otherwise open circuit.
 

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It's the ECM/ECU. I have the same issue. I'm ordering the part already. Before it didn't start, there were times I was driving and the coolant temp gauge would shoot straight to H and battery light will go on and vehicle will die. One day it died out and won't start. So for now I'm going to run it with the scanner hooked up until it comes in. I'll post again once I get the part and install it.
 
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