MG Sports Cars

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.

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

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.

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.

Is that header ceramic coated?

Yes, it is ceramic coated

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

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

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.

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?

It's not ideal but you could reverse the two wires at the coil pack. Certainly much easier and would be a quick way to check the problem.

If really really desparate
[www.youtube.com]

Ivor

I'm pretty certain that the new 3X sensor is working OK after running some tests outlined in my factory manual for this engine. However i have just installed my second Walpro in-tank pump, just in case the first one was faulty. (The original that Todd Budde installed in his 18 gal aluminum tank had begun to squeal.)
I replaced it with exactly the same model pump, i used the same internal wiring and connector and i didn't touch the external wiring which has run for 3 years.
When i turn on the ignition key i hear the pump pressurize the system for about 4 secs just lie it used to with the old pump. The problem is that the pressure gage attached to the bleed valve on the fuel rail shows no pressure and if i bleed it there s no fuel squirting out. I have checked the inline fuel filter. I also replaced the fuel regulator valve last year and the vacuum line attached to it shows no fuel in the line, which would be the case if the valve diaphragm was faulty.
Anyone got any ideas

Your pump will have polarity markings on it. Make sure that it is connected correctly. I have seen them reversed on many occasions. I have also seen them installed with the port plugs still inserted.

OK, what a very strange week. Finally installed the 3X crankshaft sensor for a third time after taking it back out and finding that on one of the wire extensions I added to the sensor's short pigtails the splice, using a crimped joint, had no continuity. Once repaired and everything was re-installed the car roared to life.
Strangely the pressure gage still attached to the fuel rail bleed port still showed no pressure so I am assuming that the gage is somehow faulty.
I drove the car many times yesterday in 80 degree weather and it started every time...until late last night when I wanted to drive it into my garage, it failed to start. I could have held the gas pedal to the floor and I'm pretty sure it would have eventually started like old times but it was late and my garage is close to the neighbors house so I didn't want to disturb anyone, there was also a strong smell of gas too. I'll wager money that i will start first time this morning.

So there we have it, new fuel pump and new 3X sensor and still the starting problem persists when hot. I've protected the sensor wiring with heat tubing and have also installed an aluminum heat shield between it and the header per member suggestions. So to recap, I have now over the last several months replaced the above 2 items, the in-tank fuel pump, teh fuel presure relief valve, the ignition control board and 3 coils, spark plugs and their cables. When it won't start I get no error codes when I scan although I'm going to carry my hand held acton scanner in the car from now on just in case.

Brian at BMC is sending me another ECM just n case mine is faulty. It will be a pain to swap them out and I probably won't get to that until I return from an upcoming business trip to Germany. I forgot to mention that I also removed all cable tie wraps and checked all wiring both in the engine compartment as well as under the dash for wires that might be suspect and found nothing wrong before tidying things back up.



Edited 1 time(s). Last edit at 06/03/2018 11:43AM by limey222.

Came home on a flatbed today. No start whilst at the shops.
After spending three hours with a Tirfor winching the Landy part way up our steep drive - I really must work out something better than that - I tried it once more and ...it started.

I almost had a Basil Fawlty moment
[www.youtube.com]
but after I calmed down I realised this failed hot start was an extension of the cold start problems I've been having recently with my Rover V8.

I think when the engine is cranking there is no ignition supply, as I noticed it fires just at the moment I release the key.
So tomorrow I'll be underneath checking the ignition feed on the starter.
Sometimes it's the little things,

Ivor

LOL...one of my favorite car-related comedy sketches.
I have a suspicion with my car that I inadvertently may have created a problem. My cooling fan was originally controlled by the ECM which is the factory method.
I later added a time delay relay circuit to have the fan run on for a length of time after I had shut the engine off. To achieve this I had to use a simple temperature sensor switch installed in the top of the radiator to control the fan rather than the ECM. The ECM probably still thinks it is connected to the fan when the engine is running but the wire is just disconnected. After a few weeks the "run-on" circuit began to malfunction (it was an aftermarket kit) so I disconnected it, but didn't revert to ECM control over the fan. What sometimes happens is that the fan is still running when i get to my destination. If it's a short time when I go to restart the car, upon turning the ignition on I find that the fan comes on, indicating that the coolant temperature is still high enough to trigger it. The engine cranks just fine but I wonder if the current draw of both the fan and the starter motor combined is sufficient to cause a problem with the ignition circuit
If I waiting a minute or two until the fan turns off and then try to start the car usually starts OK.

Is the coil opening up when it gets hot?

The OP already replaced his coils - although sometimes we replace bad with bad - so I won't add much about my non-start. Yes, there was the usual voltage drop whilst cranking, but it was the coil.
Been failing since March, I think, when we nearly had a non-start on returning from Cyprus to Gatwick airport after midnight.
The coil was beginning to earth itself. When running, I could see spikes. 10.8V normal (ballast) but brief spiking to 12V even up to 16V, and dropping to zero then back to 10.8V. I removed the coil from the clamp to isolate it, and it started fine.

New 1.5 ohm coil - job done. Only took me all day to figure that one out.

Electricity..... who needs it.

Ivor

On the GM L32 3.4 V6 there ae three coils , each one feeding two cylinders. So if a coil is failing the car would probably still start but would run very badly.

In my case the problem does seem heat-related, there is never a problem starting when the engine is cold. The next time it occurs I need to quickly take resistance reading to see if the 3X sensor still reads between 900 and 1200 ohms. If it shows a direct short or open circuit then I know that I still have an overheating 3X sensor problem, if not then I can eliminate it from my troubleshooting. The next area to check would be the ignition control module that the 3 coils are mounted on. The 3X sensor output is connected to this module and it also feeds a related signal to the ECM. The 3X sensor is low resolution and is only in play at low rpm, above 900 rpm the 24X crankshaft sensor takes over.