Reduced revs & lack of performance.

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STW82
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Reduced revs & lack of performance.

Post by STW82 » Mon Jan 21, 2019 4:30 pm

Hello MGF and TF gurus. I'm hoping someone on here will have had a similar problem giving me something to go on with fault finding my TF135 engine. I recently changed from a 1.4 16v Mems 3 setup (fitted to a Rover 100) to a 1.8 by swapping the engine and ecu but keeping the 1.4 loom I already had. Since fitting the engine and taking it out for a drive the extra power seems instantly noticeable. Until I get into the mid rev range and it just feels like it's hit a limiter. Has anyone come across anything similar or has anyone got any pointers on what to check first?

https://youtu.be/YmB-3WsJi1o

When I change gear there is physically nothing else available power/revs. But while it's getting there it's very smooth and feels to have plenty of punch.

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Rob Bell
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Re: Reduced revs & lack of performance.

Post by Rob Bell » Tue Jan 22, 2019 2:25 pm

It sounds as though it is running sweetly enough, but I agree, it doesn't sound as though you're getting the whole rev range there.

Have you got access to an EOBD reader? Would be interesting to see what the engine sensors are telling you what is happening. I *think* the harness plug is wired the same for both the 1.4 and 1.8, but as I recall, looking at the MEMS3 small plug, there are differences between models here...

With an EOBD reader, you should get a clearer idea of what the ECU is reading from sensors.

A real possibility is that if you are using the original 114 fuel pump, the injectors are running out of fuel as the rpm increases: you may need to fit a higher capacity fuel pump :)

flyingbanana
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Re: Reduced revs & lack of performance.

Post by flyingbanana » Wed Jan 23, 2019 1:51 pm

Rob Bell wrote:
A real possibility is that if you are using the original 114 fuel pump, the injectors are running out of fuel as the rpm increases: you may need to fit a higher capacity fuel pump :)
I used the same metro gti fuel pump on my vvc 160 race car as i did when it was a 1.4.

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Rob Bell
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Re: Reduced revs & lack of performance.

Post by Rob Bell » Thu Jan 24, 2019 4:21 pm

From memory, the GTi had a different pump to the SPi versions - but if not, the old Metro pump is not delivering the juice any more.

The way to tell is to still a fuel pressure gauge in the system and see what is happening. With a standard fuel pressure regulator, the fuel pressure should stay at 3.0bar what ever the engine load.

If it isn't that, then the problem is ignition related. Failing coils will give a misfire, so that's unlikely. Failing spark plugs? Compression problem? Manifold leak?

itsonlyme54
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Re: Reduced revs & lack of performance.

Post by itsonlyme54 » Fri Jan 25, 2019 5:33 pm

if its a Spi model then the fuel pump will be the problem, it simply cannot deliver enough fuel at higher rpm, been there done that one

STW82
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Re: Reduced revs & lack of performance.

Post by STW82 » Mon Mar 11, 2019 3:13 pm

Hi

Sorry, with one thing and another the car took a bit of a back seat thanks to commitments at work and a holiday. I appreciate the replies though. The car was an MPI to start with and ran fine with the previous 1.4 MGZR engine. The confusing thing was the cut in power was very neat, it didn't judder or cough so I thought it might be going into limp home mode and the ecu cut the revs. Based on the speed it was maxing in each gear compared to the max speed it should achieve at red line (I forget the standard red line value now as its been a few months). I estimated it was cutting at about 5200-5500 revs max. In the past when I have had cars with engine management issues I've basically worked my way through the sensors one by one and unplug them. I usually find the car runs much better with the sensor unplugged and the ecu reading default values rather than the incorrect values being given by a faulty sensor. First of all I unplugged the lambda sensor and gave it a run.

https://youtu.be/GjSBlukx7TQ - here is the result. Much better

I tried the lambda sensor first because I used a 4 bolt manifold on my conversion and the MEMS3 lambda (with a D shaped plug) didn't fit in the threaded boss so I used one from the 4 bolt manifold (which had the square plug) and made a loom to convert the wiring. Obviously this loom didn't work or the lambda isn't compatible.

Has anyone converted to MEMS 3 and retained the 4 bolt manifold? If so did you encounter any problems with fitting the sensor?

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Re: Reduced revs & lack of performance.

Post by talkingcars » Mon Mar 11, 2019 11:28 pm

STW82 wrote:Has anyone converted to MEMS 3 and retained the 4 bolt manifold? If so did you encounter any problems with fitting the sensor?
The first sensor should be fine for MEMS3, it is only the plug that is different.

The second, post cat sensor is only for refrence, I didn't have it plugged in on my mk2 ZS at all, it peiodcally gave a EML.
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Rob Bell
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Re: Reduced revs & lack of performance.

Post by Rob Bell » Tue Mar 12, 2019 1:58 pm

MEMS3 is very fussy about Lambda sensors - so use the one from a MEMS3 car if at all possible. I am surprised that it didn't fit in the threaded boss? Different thread???

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