MG Sports Cars

engine swaps and other performance upgrades, plus "factory" and Costello V8s

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limey222
Michael Cubbon
Portland, OR
(125 posts)

Registered:
08/01/2015 12:55PM

Main British Car:
1969 MGB GM 3.4L V6

Re: Poor starting ...... getting desperate to find reason
Posted by: limey222
Date: May 10, 2018 03:13PM

Thanks Fred, Stupid me, I learnt my lesson trying rush things last night and did something that I normally wouldn't do, I reversed the top single upper connector on ignition control module with the single connector of the air flow sensor on my cold air intake ducting, they are very close on my car and look similar. Reversed the connections this morning and she fired up straight away.

The 3X sensor is the one I replaced yesterday, I believe it samples camshaft rotation.

Now when it stops raining I can rain her nice and hot and see if it has cured my hot start problem. If it hasn't then I'm back to suspecting a fuel component.



Edited 2 time(s). Last edit at 05/10/2018 03:16PM by limey222.


DiDueColpi
Fred Key
West coast - Canada
(1254 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Poor starting ...... getting desperate to find reason
Posted by: DiDueColpi
Date: May 10, 2018 05:05PM

You have 3 rotational position sensors Michael.
One for the cam position on the top front of the engine, this should be a hall effect 3 wire sensor with a 4'' or so pigtail on it.
#2 is the 3X sensor for the crank, it's on the lower right side of the engine and has a two wire plug receptacle on it.
#3 is the 24X sensor on the front of the engine.

Cheers
Fred


limey222
Michael Cubbon
Portland, OR
(125 posts)

Registered:
08/01/2015 12:55PM

Main British Car:
1969 MGB GM 3.4L V6

Re: Poor starting ...... getting desperate to find reason
Posted by: limey222
Date: May 10, 2018 08:49PM

Thanks for setting me straight Fred, I had forgot that there were three rotational sensors, I replaced all three when I first bought the engine 4 years ago. So I replaced the camshaft rotational sensor last night. The other one that I just purchased is the #X sensor, if its easy to swap out I'll do it tonight. Hopefully the 24X sensor is as durable as you say. Looking at the diagram in the GM service manual it looks like it may be swappable while not having to remove the crankshaft balancer assembly, can you confirm that.

BTW in case you haven't already realized, I'm at that "a little knowledge is dangerous" stage, but I"m a quick learner.



Edited 1 time(s). Last edit at 05/10/2018 08:50PM by limey222.


limey222
Michael Cubbon
Portland, OR
(125 posts)

Registered:
08/01/2015 12:55PM

Main British Car:
1969 MGB GM 3.4L V6

Re: Poor starting ...... getting desperate to find reason
Posted by: limey222
Date: May 10, 2018 10:01PM

Fred, bad news, I forgot just how close Bill Guzman's headers come to the 3X sensor. There was about a 1/8" gap between the middle branch pipe and the top portion of the 3X sensor when installed. I had to pack a piece of header wrap material into the 1/8" gap to try and insulate the sensor. If I need to swap it out i will have to unbolt the passenger side header and disconnect it lower down as well, not very easy to access without a lift, it's very tight in there spacewise.
Hopefully it's OK, it was new 3,500 miles ago



Edited 1 time(s). Last edit at 05/10/2018 10:02PM by limey222.


MGBV8
Carl Floyd
Kingsport, TN
(3349 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Poor starting ...... getting desperate to find reason
Posted by: MGBV8
Date: May 11, 2018 10:32AM

Is that header ceramic coated?


limey222
Michael Cubbon
Portland, OR
(125 posts)

Registered:
08/01/2015 12:55PM

Main British Car:
1969 MGB GM 3.4L V6

Re: Poor starting ...... getting desperate to find reason
Posted by: limey222
Date: May 11, 2018 01:49PM

Yes, it is ceramic coated


MGBV8
Carl Floyd
Kingsport, TN
(3349 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
79 MGB, Buick 215

authors avatar
Re: Poor starting ...... getting desperate to find reason
Posted by: MGBV8
Date: May 11, 2018 02:50PM

That & the insulation may help. Not much air gap, though.



ex-tyke
Graham Creswick
Chatham, Ontario, Canada
(990 posts)

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

authors avatar
Re: Poor starting ...... getting desperate to find reason
Posted by: ex-tyke
Date: May 11, 2018 03:05PM

Doesn't Brian McCullough have a 3.4EFI with a Guzman exhaust kit - wonder if there is something different in his installation.


DiDueColpi
Fred Key
West coast - Canada
(1254 posts)

Registered:
05/14/2010 03:06AM

Main British Car:
What if the Hokey Pokey really is what it's all about?

authors avatar
Re: Poor starting ...... getting desperate to find reason
Posted by: DiDueColpi
Date: May 11, 2018 08:44PM

Those sensors and heat are mortal enemies!
I would make up a small sheet aluminum shield for it. Fashion it to promote as much cool airflow around the sensor as possible.


limey222
Michael Cubbon
Portland, OR
(125 posts)

Registered:
08/01/2015 12:55PM

Main British Car:
1969 MGB GM 3.4L V6

Re: Poor starting ...... getting desperate to find reason
Posted by: limey222
Date: May 26, 2018 02:49PM

Grrrrr......really mad with myself. I installed a new 3X crankshaft rotational sensor earlier in the week. Miserable task, had to pull the alternator, cast bracket and Guzman header to access it. Made a nice heat shield out of sheet aluminum to protect it held in place by the same bolt that anchors the sensor. Put it all back together and tried to start the car....wouldn’t fire at all. So I connected my laptop , opened up my monitoring software and cranked the motor. Checked for DTC’s and there it was , the dreaded 3X error code. So I am faced within two possibilities, either the new sensor is bad or I wired up the new pigtail connector wrong. The problem was that although the two wires going down to the sensor had different color codes, the pigtail connector from the same manufacturer (Standard) of the sensor had the same color for both wires. I assumed that since it was a two wire sensor employing a permanent magnet pick up that it could be wired either way. But if it that is not true then I had a 50/50 chance of getting it right, or wrong in my case. Now I have to pull it all apart again since the space down there is too restrictive to achieve anything without removing the header, I have lacerated hands and arms to prove it. Here is where I have a question, I know that this will damage the ceramic coating on the header but I see an opportunity to hammer a slight indentation in the header just below the weld line where the three branches come together. The intent is to create clearance to enable me to pull the 3X sensor anytime I want to in the future without having to remove everything else. At the same time I plan on extending the pigtails wiring by soldering an extra length of wire to them and using shrink wrap. This would allow me to use some plug-ing connectors higher up where access is far easier. I would use some of the removable plastic convoluted protective tubing over the entire iength as well. I reckon that I will have to dent the header tube in about 3/8” for a 1” length to achieve the necessary clearance, does anyone see a reason why I shouldn’t do this?
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