Vauxhall Corsa B - Engine hesitation

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Wed 22 Nov 2017 10:08
Vauxhall Corsa B - Engine hesitation - Lydscorsab
Hi all

I recently bought a Vauxhall Corsa b 1.2 16v 2000 reg. It seemed to drive fine and then partway home the eml came on as I hit 60mph and the engine seemed to struggle to reach 65mph. When I dropped the revs and changed gear the eml went off and it was fine at a lower speed. Also, I noticed that from a cold start it would hardly move in 1st gear with my foot to the floor. I’d have to restart the engine and then it would be fine.
I took it to a garage and they plugged in a diagnostic machine and couldn’t find any fault codes. They did a test on the exhaust gases and concluded the catalytic converter was blocked. They recommended a cat cleaner. Used the cat cleaner for a good 20 plus miles and still no change. Took it back and got a new cat. The catalytic converter hasn’t solved theissue. The engine is still hesitating at high speed. I’ve changed the spark plugs and coil pack. Disconnected the battery to try and reset the ecu. No change.
The cars not long been serviced as the oil is still golden.
I’m going to try changing the air filter, fuel filter, maf sensor and also the crankshaft sensor. It’s going back to the garage today as they suspect the lambda sensor may need a clean/change.

Any other ideas?

Edited by Lydscorsab on 22/11/2017 at 10:09

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Wed 22 Nov 2017 12:11
Vauxhall Corsa B - Engine hesitation - Cyd

As long as the garage are happy to continue their "diagnosis by guesswork" approach and are willing to let them keep changing parts (at no cost to you), then let them.

Obviously, we can't see or inspect the car, so anything on here is a guess too. All the same it sounds like fuel starvation to me. When did it last have the fuel filter changed? If you'd like to see what a 100,000 mile petrol filter looks like, I show you here:

https://www.youtube.com/watch?v=8aZLTbG993Y&t=246s

You could use a suitable live data app (I use Torque Pro) and in particular monitor the fuel flow rate and see if it is hitting a critical point that it won't climb above. If so try the filter (never a bad thing to put on a new one) but it could also be the pump failing. Or a combo of the two.

Edited by Cyd on 22/11/2017 at 12:14

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Wed 22 Nov 2017 12:32
Vauxhall Corsa B - Engine hesitation - Railroad.

A 2000 car is pre-EOBD legislation, but if it is EOBD compliant (and some cars were before it became a legal requirement for petrols 1.1.2001, and diesels 1.1.2004) you should use a suitable scantool to obtain live data readings and fuel trim information. Just changing sensors in the hope you're going to stumble across the fault will solve nothing and cost you more than the car's worth. Use a vacuum gauge to measure inlet manifold vacuum. That will tell you a lot about the mechanical state of the engine.

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Wed 22 Nov 2017 12:38
Vauxhall Corsa B - Engine hesitation - Lydscorsab
I think a vacuum gauge was used at the garage and that’s when they suggested the new cat.

I’ll let you know how I get on later
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Wed 22 Nov 2017 12:50
Vauxhall Corsa B - Engine hesitation - Railroad.

A vacuum gauge will diagnose a blocked exhaust, but it won't be able to pinpoint that blockage to the catalyst. The rear exhaust silencer may also be blocked, and since it's the part that takes the longest to warm up it's the most likely.

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Wed 22 Nov 2017 12:35
Vauxhall Corsa B - Engine hesitation - Lydscorsab
Thanks for your reply.

The parts i’ve bought are off my back and not the garage suggestion. I’m going to change the fuel filter, however the car has only done 45k.

How would I use Torque Pro?
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Wed 22 Nov 2017 12:54
Vauxhall Corsa B - Engine hesitation - Railroad.

45,000 miles since the fuel filter was last changed?

Please explain to me why mileage rather than time is crucial when changing it.

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Wed 22 Nov 2017 14:03
Vauxhall Corsa B - Engine hesitation - Lydscorsab

45,000 miles since the fuel filter was last changed?

Please explain to me why mileage rather than time is crucial when changing it.

Update, a fault code has come up and it’s the lambda sensor causing the fault.

Edited by Lydscorsab on 22/11/2017 at 14:08

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Wed 22 Nov 2017 14:26
Vauxhall Corsa B - Engine hesitation - Railroad.

Update, a fault code has come up and it’s the lambda sensor causing the fault.

You mean the lambda sensor is where the fault is being reported from. It doesn't necessarily mean the lambda sensor is the fault. The sensor tells the ECM the state of the fuel/air mixture, which in turn either adds fuel or removes fuel depending on the information it receives. Its aim is to run the engine between rich and lean, passing through the ideal point each time to maintain 'Lambda 1, which is 14.7:1 air/fuel ratio. This is what's needed to make the catalyst work. Because the ECM receives data from the O2 sensor and then responds to it it's known as 'Closed Loop'. Any mechanical fault with the engine, fuel injectors, restricted air intake or exhaust, and a whole load of other things will affect the efficiency of combustion. This in turn will affect the O2 sensor data. The ECM is not capable of telling the difference between an O2 sensor giving a bad reading because it's faulty, or giving a bad reading because there's some other reason why engine isn't running properly. Before you spend money on a new sensor you need to find out whether or not it's telling the truth. If it is then replacing it won't solve anything.

On the other hand it's very good practice to renew the O2 sensor anyway if you renew the catalyst.

Edited by Railroad. on 22/11/2017 at 14:30

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Wed 22 Nov 2017 15:48
Vauxhall Corsa B - Engine hesitation - Lydscorsab
What an absolute nightmare!! I’ve bought a maf sensor anyway just in case. So hopefully it is just a faulty lambda sensor and nothing more.

The car runs perfect through the rev range till I get to 60. Its so frustrating.
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Wed 22 Nov 2017 17:45
Vauxhall Corsa B - Engine hesitation - elekie&a/c doctor

If the Eml has come on, then hopefully there will be some fault code stored .Also you need to find somebody that can analyse the data from the engine control unit and make some assesment as to what is going on.Looks like the garage are shooting in the dark.Common fault for these to flag lambda sensor,when in fact the problem is the Maf sensor.

Edited by elekie&a/c doctor on 22/11/2017 at 17:46

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Thu 23 Nov 2017 10:15
Vauxhall Corsa B - Engine hesitation - Railroad.

The chemically correct air/fuel ratio for a petrol engine is 14.7:1. That's 14.7 parts of air to 1 part of fuel. However it should be noted that this figure is by mass, not by volume.

Mass air flow sensor information is displayed on most scantools in g/s, grams/second. Do the following to establish whether or not you MAF sensor is reading correctly or not.

Select live data on a scantool to show MAF data. With an assistant drive the car up the road and hold it in second or third gear. Drive at full throttle up to about 5,000rpm and note the point where the MAF reading peaks in g/s. Now multiply that figure by 0.8. The answer should be more or less equivalent to the engine's Brake Horse Power. If your reading falls well short then the MAF needs replacing.

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Thu 23 Nov 2017 12:25
Vauxhall Corsa B - Engine hesitation - Cyd

Now multiply that figure by 0.8.

DIVIDE MAF by 0.8 to give horsepower

MULTIPLY horsepower by 0.8 to give MAF

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Thu 23 Nov 2017 12:45
Vauxhall Corsa B - Engine hesitation - Railroad.

Yeah thanks Cyd. You're right, that's actually what I meant. Peak airflow should be roughly 0.8 of brake horsepower. So a 150BHP engine's peak airflow should be around 120g/s.

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Thu 23 Nov 2017 13:52
Vauxhall Corsa B - Engine hesitation - Lydscorsab

If the Eml has come on, then hopefully there will be some fault code stored .Also you need to find somebody that can analyse the data from the engine control unit and make some assesment as to what is going on.Looks like the garage are shooting in the dark.Common fault for these to flag lambda sensor,when in fact the problem is the Maf sensor.

The lambda sensor was replaced today and it hasn’t cured the problem. I have a Bosch maf sensor on its way. I’ll get that fitted and give another update...

Edited by Lydscorsab on 23/11/2017 at 13:53

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Thu 23 Nov 2017 22:19
Vauxhall Corsa B - Engine hesitation - blindspot

maf sensor . thats why it wont run from cold. cheap quick fix.

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