MG Sports Cars

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

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limey222
Michael Cubbon
Portland, OR
(129 posts)

Registered:
08/01/2015 12:55PM

Main British Car:
1969 MGB GM 3.4L V6

Poor starting ...... getting desperate to find reason
Posted by: limey222
Date: March 03, 2018 10:45PM

OK fellow members, this is not the first time I've asked about this problem but it still exists.
Here's the background:
93-95 GM 3.4L V6 + T5
Stock EFI and ECM
The car starts OK and runs great, I drive a few miles and maybe go into a grocery store. When I come back out she just won't start, turns over just fine. If I hold the gas peal down so the ECM shuts off the fuel supply to the injectors to clear out any flooding she will eventually start with a cloud of smoke for 5 seconds. Today however she just wouldn't restart at the grocery store. She never even occasionally fired during multiple attempts. Cranking was very strong but nothing except eventually a strong gas smell. I had to call AAA for a flatbed, after another 10 mins I thought I would try one more time....and yes, she started so I had to cancel the tow truck.

So what have I done to try and solve this over the months, I've replaced the injectors, fuel pressure relief valve, coils and ignition control board, spark plugs, all sensors, etc and the problem still occurs. Fuel pressure is within specs, I see no error codes on my laptop via diagnostic port that I've installed. I replaced the injectors and pressure relief valve because I thought that perhaps one or more cylinders were being flooded due to a leaking injector or a blocked relief valve...but no.

I'm getting pretty desperate right now becasue the cause continues to elude me. Can any one help?


rficalora
Rob Ficalora
Willis, TX
(2529 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Poor starting ...... getting desperate to find reason
Posted by: rficalora
Date: March 04, 2018 08:57AM

Sounds like it could be heat soak. Is your fuel line close to the exhaust or block?

Also, you say fuel pressure is good. Have you watched it while cranking when it's not starting? Or test the voltage at the fuel pump when it's acting up. Possible you're not getting full voltage when hot due to a poor ground or an under sized power lead.


MG four six eight
Bill Jacobson
Wa state
(281 posts)

Registered:
10/23/2007 02:15AM

Main British Car:
73 MGB Buick 215, Eaton/GM supercharger

Re: Poor starting ...... getting desperate to find reason
Posted by: MG four six eight
Date: March 04, 2018 11:29AM

Michael,

Since you are using a stock ECM, are you able to connect a scan tool to it?

If you are, then I would use a scan tool to monitor the data during the no start condition. Since it sounds like that it may be flooding, pay close attention to the coolant and air temp readings. If the temp values are cooler then the actual temperature, then the ECM will add fuel.

Bill


limey222
Michael Cubbon
Portland, OR
(129 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: March 04, 2018 01:31PM

Bill,
thanks for the suggestions and yes I do have a 2.0 diagnostic port wired in despite the system being 1.5. I can get full readings on my hand-held scan tool and my laptop with suitable software. I will check the temp values that suggest as that's not been checked before. Knowing how to interpret some of the readings has not ben my strong point outside of there either being a fault code or not. This time of year the engine rarely reaches normal operating temperature on a short errand trip. However even in the heat of summer when the electric fan is on most of the time I still have the starting problem (which initially led me to investigate heat soak).


DiDueColpi
Fred Key
West coast - Canada
(1259 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: March 05, 2018 01:58AM

If you can get your scanner to show data while cranking, check the output from the crank angle sensor Michael.
It's very common for the GM sensor to fail when it's hot.
The sensor isn't critically required while the engine is running. If it fails the ECU ignores it and goes into limp mode. Once you shut the engine down however it then won't restart until the sensor cools and becomes active again. While you are cranking with an inactive sensor you will not have a spark, but you will have fuel as that function derives its signal from the cam position sensor. That leads to the impression that the engine has flooded.

Hope that's helpful.
Fred


limey222
Michael Cubbon
Portland, OR
(129 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: March 07, 2018 03:46PM

OK I'm running Scan9495 for V6 software on my laptop. I get no DTC's and I'm not sure how to interpret some of the readings. For instance in the lower part of the attached photo there are condition that sometimes are highlighted in green. Notably "engine closed loop" and "CAM signal" the engine closed loop message appears to not lit until the engine is warm then it is high lighted in Green. The CAM signal flashes on and off v erratically all the time.
I always thought that the closed loop should be green until the engine reaches operating temperature then the green highlight should disappear....I'm lost
Can anyone help?
IMG_0198.JPG



Edited 1 time(s). Last edit at 03/07/2018 03:48PM by limey222.


pcmenten
Paul Menten

(242 posts)

Registered:
10/08/2009 10:40AM

Main British Car:


Re: Poor starting ...... getting desperate to find reason
Posted by: pcmenten
Date: March 09, 2018 07:44PM

Hi Michael,

'Open-loop' means that the ECU is using 'hard-coded' values for spark and fuel. This is the mode used while the engine is warming up. 'Closed-loop' means the ECU is using the sensors to adjust spark and fuel values. Closed-loop is the mode used when the engine is warmed up.

Sounds like the trouble starts when the engine warms up and the ECU switches to closed-loop.

I'll take a closer look at the picture to see if anything jumps out as strange.

Paul

Edit:

> It seems odd that the coolant temp is 46 degrees and the engine is in closed-loop.
> The spark timing is 32 degrees when the engine is at 1000 RPM. That seems very high.
> I see a message that the 'CAM signal missing'. I'm not sure what that means. Is that the camshaft angle?

Question: is the EGR installed and working? Does the engine have an AIR system? These are called 'pollution control' devices but they serve other functions, too. The AIR system helps prevent the Oxygen sensor from fouling while the engine is warming up. Once the engine is warm and the Oxygen sensor starts to work, the ECU typically diverts the air to the oxidation side of the catalytic converter to help keep the cats from fouling. I'm not familiar with the controls of this engine, so I don't know if a Air Injection Reactor (AIR) pump is part of the strategy.

The Oxygen sensor is reading .446 volts. Have you seen it change? If the Oxygen sensor is fouled, it will cause the fuel metering to be off. Typically, engine management strategies try to run the engine slightly lean under part-throttle operation. That would push the reading of the Oxygen sensor up to a value like .800 volts. If the Oxygen sensor is fouled and isn't able to properly read Oxygen levels, the ECU will be trying to lean out the fuel curve.

EGR (Exhaust Gas Recirculation) is used to reduce Nitrous Oxide (brown smog) by reducing combustion chamber temperatures by adding atmospheric volume to the air/fuel mixture at part throttle operation. When combustion chamber temperatures reach 1600 degrees F, Oxygen and Nitrogen will react with each other. Adding inert exhaust gasses to the mixture lowers the average temperature of the gasses. This changes the dynamics of the combustion process. One of those changes is to increase the part throttle compression ratio, which increases thermodynamic efficiency. Another change is to reduce the density of the Oxygen in the mixture. Because of the increased volume of atmospheric volume in the combustion chamber, the average temperature is lower and the speed of the flame front is lower. This means that you need more spark advance. If the EGR is detached, then the ECU's base table for the spark advance needs to be modified by reducing spark advance values.

I hope that helps.

Paul



Edited 1 time(s). Last edit at 03/09/2018 08:29PM by pcmenten.



302GT
Larry Shimp

(188 posts)

Registered:
11/17/2007 01:13PM

Main British Car:
1968 MGB GT Ford 302 crate engine

Re: Poor starting ...... getting desperate to find reason
Posted by: 302GT
Date: March 14, 2018 01:43PM

I once helped someone with a V6 Camaro (FI, do not know what year). It seemed to be "flooding" when hot starts were attempted. The fix was to replace the temperature sensor since it never recognized that the engine had warmed up and did not need an enriched fuel mixture.


MGBV8
Carl Floyd
Kingsport, TN
(3450 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: March 27, 2018 10:55AM

Have you tried another ECM?


limey222
Michael Cubbon
Portland, OR
(129 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: March 29, 2018 06:33PM

No EGR fitted and no air system, I donít think that many if any running the 94 3.4L have those systems installed. They were never part of my instructions from Brian at BMC. Going to check if the CAM signal sensor is bad or itís wiring damaged just in case. It actually goes on and off all the while, someone told me that was normal.



Edited 1 time(s). Last edit at 03/29/2018 06:36PM by limey222.


DiDueColpi
Fred Key
West coast - Canada
(1259 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: March 29, 2018 08:25PM

Your cam sensor is a hall effect sensor and its "on" for 1/2 of the cam rotation and "off" for the other 1/2.
The ECU uses that information to determine which stroke the crankshaft is on.
So "someone" was technically correct. But your scanner program shouldn't really report the cam signal as off and on on a running engine.
Also like Paul says, 46' temp. and closed loop don't really fit together.
With whats happening here you should have the MIL on but the screen says no DTC's
I would suggest trying another scanner as your current readout doesn't appear to be possible.

Just to muddy it up a little. Your intake temp is higher than the engine temp. Is it possible that they are backwards?

The whole thing runs on FM!
Cheers
Fred


limey222
Michael Cubbon
Portland, OR
(129 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: March 30, 2018 09:02PM

Fred,
Thanks for helping me wade through the data and status, I'm still very new to this. For a start should I try swapping the temp connections to reverse the apparent anomaly of having intake temp higher than engine temp and observe the resultant effect?

What exactly is MIL?


limey222
Michael Cubbon
Portland, OR
(129 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 06, 2018 12:49PM

OK, attempting to revisit this continuing problem again in the hope that someone new can shed some light on its cause. Please go to my original post #1 for a description of the fault ad how my car is configured so I don't have to repeat all of that info.
The car car still starts immediately when cold. After running for a short trip it is questionable whether it will start again, twice this weekend it has restarted a couple of times without a problem and then the next time refused to fire. It happened once on a gas station forecourt and then again at home when I wanted to drive it into my garage. The only difference this time compared to historically every other time, it actually threw up a code stating a 24X error which at first glance seems to reference the crankshaft sensor. However after more research it appears that it can also point to coil pack problems as well as some owners who have a GM 3.4 V6 conversion have stated.

BTW, once started the car runs normally. The trick to start the car when experiencing this problem is to wait 10-15 minutes then it will start. Members have pointed out that it could be a vapor lock, caused by the fuel line routing near the exhaust (not in my case), the fuel lines on top of the block overheating (this area is exactly the same as the stock configuration on a Camaro with this engine so not likely), or flooding caused by an injector sticking open or a problem with the fuel pressure relief valve ( I have replaced all with new parts).

I have also replaced plugs and leads, the coil packs and the motherboard (spark control) that they are mounted on.

The only way to possibly start the car instead of waiting 10-15 minutes, is to hold the gas pedal down to the floor while cranking which turns off the injectors then it might fire. Thee si a strong gas smell when this happens. So it points to a flooding situation but if it is, I can't find the cause be it fuel delivery or spark control.


rficalora
Rob Ficalora
Willis, TX
(2529 posts)

Registered:
10/24/2007 02:46PM

Main British Car:
'76 MGB w/CB front, Sebring rear, early metal dash Ford 302

authors avatar
Re: Poor starting ...... getting desperate to find reason
Posted by: rficalora
Date: May 06, 2018 09:15PM

Did you ever check the things Fred suggested?
* Different scanner to see if yours is reading things right
* Figure out why intake temp is higher than engine temp
* Crank angle sensor - which based on his description of no spark but fuel ok, would seem to account for the strong gas smell when it starts.

Also, long shot, but if your fuel rail isn't stock GM setup, maybe a fuel line is too close to something hot. I recently did some digging on a similar problem my son's Jeep Wrangler 4.0 had and found a tech bulletin saying the line on #3 injector was too close to exhaust so they recommend an insulation kit. I used a spark plug wire insulator (the type designed for plug wires that are close to headers) by splitting it open and wrapping the injector. It solved the problem. You could have something similar going on.


limey222
Michael Cubbon
Portland, OR
(129 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 07, 2018 01:47AM

On that particular occasion I suspect that since the engine was cold and outside air temp was quite warm it would show what it showed on the scan. As the engine warmed up it would have reversed the suspected anomaly.

I have both a well respected program on my laptop and a hand held scanner.

The engine and EFI system is completely stock out of a 94 Camaro.

I have both a cam sensor and a crank sensor on order.

In the screen shot of the scan in a previous post where intake temp is shown as being higher than engine temp the engine closed loop message is not highlighted in green meaning to my mind that it wasn't in closed loop mode.

I really do still suspect a flooding situation that after 10-15 minutes has time to dissipate. Why it could happen is another subject since I have replaced all injectors and the pressure relief valve,



88v8
Ivor Duarte
Gloucestershire UK
(603 posts)

Registered:
02/11/2010 04:29AM

Main British Car:
1974 Land Rover Lightweight V8

Re: Poor starting ...... getting desperate to find reason
Posted by: 88v8
Date: May 07, 2018 04:20AM

....the fuel lines on top of the block overheating (this area is exactly the same as the stock configuration on a Camaro with this engine so not likely).... .

But that was with older fuels, and there's more space under the Camaro bonnet.

Ivor


limey222
Michael Cubbon
Portland, OR
(129 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 07, 2018 09:57AM

Still not convinced that its a heat soak problem affecting fuel lines on top of engine. However I will take some readings with my infrared gun.


limey222
Michael Cubbon
Portland, OR
(129 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 10:18AM

OK now I'm really confused. I received 3 new AC Delco coils plus a new "motherboard" that they are installed on. I also replaced the cam sensor but have not replace the crankshaft sensor at this time as it is a major job on my car. I will have to remove the front grill, radiator,cooling fans and crankshaft pulley just to get to it, could GM have put it in a worse location. Anyway after all of this the car would not start or even fire, it was running before I did the work. I thought that perhaps I had the plug leads wrong so I went online to check. I can't trust the factory manual in this area as there appears to be a typo on the diagram. Online wasn't much better as there was contradicting diagrams there too for the 94 Camaro 3.4L V6 engine.
Has anyone got a trustworthy diagram that I can use?
Today I plan on going over things again to make sure I didn't make a mistake last night. I may even put the old cam sensor back in because i know that the car ran with it. I just had an intermittent signal from it when scanning the running engine.


DiDueColpi
Fred Key
West coast - Canada
(1259 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 12:56PM

Here you go Michael.
IMGP0085.JPG
The firing order and the coil numbering is correct. The position of the coil pack is not as the diagram is for a FWD.
IMGP0084.JPG
Just for clarity the crank sensor that I was referring to is the low resolution 3X sensor located on the lower right of the engine.
The high res. 24X sensor at the front pulley rarely fails.
IMGP0086.JPG
Here is the correct wiring diagram as well.
IMGP0081.JPG


DiDueColpi
Fred Key
West coast - Canada
(1259 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 01:00PM

IMGP0082.JPG
IMGP0083.JPG

Hope that helps some.
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