Coolant temperature sensor


Evening everyone,
Iv got a quick question…
would the ECU Coolant temperature sensor cause the car (MK1 GTO N/A 1991) not to start?
Even though it seems to test correctly…

I recently sold my pride and joy to a chap after never having any bother with it at the whole time I owned it. (Yes a few of the usual GTO problems, but with preventative maintenance it never let me down.)
I had a phone call off him saying it wouldn’t start. I felt obliged to help the guy out so I said I’d look into it. It was a private sale, but I would always help anyone where I can.
Having owned numerous GTO’s and worked on 10’s of them and 3000GT’s I was sure it would be a simple fix.

Symptoms are;
Will start but only after about 30 seconds of cranking.
Won’t rev for the first 30 seconds.
After that all is as usual, goes well, pulls well.
Once warm starts spot on.

I would be incredibly greatful if someone could answer my question,


Crank sensor or fuel pump issue?


Really don’t think it’ll be related to the temp sensor.
Sounds like a fuelling issue to me. The cold start time MAY change if the fuel tank is full (when compared to empty) and/or parking the vehicle on an incline and trying again when cold. If so I’d say fuel pump.
Hope that helps.


I would start from checking the ECU. This is the first thing to do when problems with engine. Ones you have done that, you are sure it might be some components on engine.
I wonder if the new owner gave car a hard drive and reving it a lot.
See inside ECU if there is a burn somewhere or capacitor exploded.


Thanks, it now starts every time after changing the sensor but has to spin for a few seconds.
So I think there must be a fuel pump issue too.
To be on the safe side the ECU is going away to be checked.
I’ll have an update once it’s back :+1:


@ne_gto Tell the buyer to come and join us, lots of technical data and help within the club ! :+1:


Ok, small update.
I thought I’d double check over everything, incase I’d missed something.
Tested all the sensors, MFI relay. All good. Good voltages.
Then tested the ECU outputs.
Also checked the fuel pump for the voltage issue.
Fuel pump is getting 12.8v upon cranking.

This is all with a warm engine. When hot I can stop and start it as many times as you like, sometimes spins a second longer then normal but that’s it.

Tomorrow I’ll test again when it’s all cold, as it’s only first cold start of the day the issue starts. When it doesn’t start, it is like it’s not getting fuel… then it will gradually fire up, then won’t rev. 2 minutes later, it’s a different car. Revs up as normal and goes well.


Hi @ne_gto
Glad you are getting there with the car.
There is loads of info on this kind of issue within the massive technical sections we have on the forum which are opened if you/or the new owner become full members. I can’t link you into the topics I found whilst looking for my own car with fuelling issues as these are only readable to full members.
I see you have been a member since 2011, so as you know this is a great club full of help, info and so much more.
The membership fee keeps this great forum and all the technical info going.
Hopefully the new owner will pop on the forum and join up.


When the car is cold; low voltage 8v or below feeding into the MFI, sale voltage at fuel pump.
So the fuel pump is running but you can hear it’s not up to speed.



As @jensenrichardson said newbie section is for newbies, please join for continuing technical support.

Closed topic till then sorry, only fair to others.