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2001 Taurus 3.0 2v
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Discussion Starter · #1 ·
Hai all, I have 2001 bull with the 12 valve Vulcan engine. In the past couple of weeks I noticed a little bit of engine surging under light acceleration or neutral throttle. It would rev up 100-200 rpms and then drop and the car would slow when the rpms dropped. It would especially do this uphill and at highway speeds. It would be perfectly fine under heavy acceleration. Just this week I got a scan tool and decided to graph my fuel trims and rpms on my normal drive to work. (about 25-30 minutes of highway) It didn’t surge, but this time when I let off the gas the rpms went from 2,300 to 2k and it held the car back. I would accelerate again and it was just fine. When I got to work I looked at the graph and around that time the computer said my coolant temp was -22 degrees and my engine was at 8,300 rpms. The long term fuel trim for bank 2 hit 49.2% at that time too. Long term fuel for bank 1 was from 0-1.6% the entire time. I’ve done some poking around and all of my fuses look fine, the body grounds are clean and are grounding. The ground on the transaxle has a bunch of stuff on it but it reads 12 Volts when tested. I’ll clean it up tonight and see how much joy that gets me. Any other ideas?
 

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Bad coolant sensor will effect the fuel trims. You maybe want to replace sensor or at least measure the resistance. How's you temp gauge? I think you have one for the gauge and one for the PCM. There has been a few posting about issues and bad sensor, it screws up the fuel mixture because it think the engine is warming up.
 

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2001 Taurus 3.0 2v
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Discussion Starter · #3 ·
The computer sees it climb up from ambient temp to 190 idling within about 10 minutes. The thermostat is a 192 degree one, and it sits at about 190-192 idling. Driving at highway speeds it doesn’t get higher than 216. Fans come on when started and shut off when it hits 190 and I assume they operate somewhat normally. My temp gauge on the other hand, 190 is sometimes the bottom end of the normal area on the gauge, sometimes it’s smack in the middle. I know there’s one sensor that looks new on top of the housing and then one from the hose that I assume comes from the heater core, idk which is which but what resistances should I be looking for on them?
 

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So the computer sees a correct functioning temperature is what you are saying? Is the -22 degrees intermittent? You have cleaned the PCM ground to the firewall?
 

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2001 Taurus 3.0 2v
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Discussion Starter · #5 ·
I think the computer sees a correct temp, the -22 was intermittent and happened at the same time as the other intermittent issues. I have not cleaned the pcm ground to the firewall, I’ll do that when I clean the other ground.
 

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My temp gauge on the other hand, 190 is sometimes the bottom end of the normal area on the gauge, sometimes it’s smack in the middle. I know there’s one sensor that looks new on top of the housing and then one from the hose that I assume comes from the heater core, idk which is which but what resistances should I be looking for on them?
The "sender" with the brown connector goes to the gauge in the instrument cluster. It should be 275 ohm when cold and 18-20 ohm at operating temperature (Haynes 3.6.3). If that is the one that looks new, perhaps the previous owner also noticed the problem with the gauge.

The sender operates completely independently from the PCM. Does the gauge misbehave at the same time the scantool reports -22 degrees?
 

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2001 Taurus 3.0 2v
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Discussion Starter · #7 ·
The gauge doesn’t misbehave. The sender to the pcm appears to operate correctly except when it reads like -22, but that’s at the same time that the pcm reads 8k rpm and everything else goes a bit wonky. I can barely fit my probes to touch the pins, so I’ll try to get some alligator clips tomorrow and go from there.
 

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Slight misunderstanding. I think in the 2001 model the instrument panel gauge is still separate. Near the thermostat housing there are two sensors: one is called the "sender" (brown connector) which is a 1-wire connection to the gauge; the other is the ECT sensor (grey connector) which is a 2-wire connection to the PCM. I thought that from 2003 onward, there is only the ECT sensor to the PCM and the PCM in turn sends the temperature info to the instrument cluster (which displays it as a number).

If the gauge is sometimes at the bottom of the scale in stead of in the middle where it should be, that might be an indication of where the bad connection is. The sender for the instrument panel is just a variable resister with one side to the engine block and the other going to the gauge. So either the 12 V to the instrument panel is not reliable or the engine block is not properly grounded.
 

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2001 Taurus 3.0 2v
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Discussion Starter · #9 ·
So I cleaned the ground in the transaxle and the pcm to the engine. I can barely get to the pcm ground to the firewall and my one wrench is too long. There is some surface rust that came off after a couple seconds just brushing the outside, but I’ll get a stubby wrench and take it off to fully clean it. I measured the grey and brown connectors at cold and operating temperatures. One probe on a pin and the other on a bare spot on the engine for the brown. As for the gauge, it doesn’t move suddenly, but where the pcm reads temp around a certain point and it is consistent, the cluster moves in that range but it will slowly climb to the middle of the gauge the longer I drive. I paid more attention to my graphs on my scan tool on my drive today and the pcm will seemingly randomly read a crazy low number and sometimes but not always the revs will be a crazy high number. The gauges do not read this but the scan tool will. Could the grey connector sender be bad and sending crazy readings that would freak the system out like that?
 

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So I cleaned the ground in the transaxle and the pcm to the engine. I can barely get to the pcm ground to the firewall and my one wrench is too long. There is some surface rust that came off after a couple seconds just brushing the outside, but I’ll get a stubby wrench and take it off to fully clean it. I measured the grey and brown connectors at cold and operating temperatures. One probe on a pin and the other on a bare spot on the engine for the brown. As for the gauge, it doesn’t move suddenly, but where the pcm reads temp around a certain point and it is consistent, the cluster moves in that range but it will slowly climb to the middle of the gauge the longer I drive. I paid more attention to my graphs on my scan tool on my drive today and the pcm will seemingly randomly read a crazy low number and sometimes but not always the revs will be a crazy high number. The gauges do not read this but the scan tool will. Could the grey connector sender be bad and sending crazy readings that would freak the system out like that?
On my G-4's, the tab on the firewall makes it hard to reach the bolt. I used a block of wood and hammer to bend that tab down a bit so straight line access for quarter inch extension. Then easy.
-chart-
 

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2001 Taurus 3.0 2v
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Discussion Starter · #11 ·
Thanks for the trick chart, that worked. That ground had rust spots all over and part of the braided cable had rust. Cleaned all surfaces and reattached, but the problem still persists.
 
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