Engine won’t rev up

[LozB]

Hi there

I've recently bought a 'spares or repair' 2001 MR2 Roadster as a project for a charity challenge European road trip I'm doing with a friend this summer.

The car hasn't been on the road for a couple of years and but is reasonably structurally sound, decent bodywork and has a good interior and roof

First job on the list of many is to get the engine running.

We charged the battery and turned the ignition and it started first time, much to our delight.  However whilst tickover was fine once we tried to rev the engine it got a bit lumpy and wouldn't rev above about 2500/3000 rpm. It kind of feels like the engine is being starved of fuel or air once you try and rev past this point. Tick over is smooth, no smoke or nasty knocks.

There was an EML light so we plugged in a OBD reader and got P0120 which is throttle position sensor.  We ordered a new one on eBay and fitted it today. Whilst the fault code has now gone the engine still won't rev past 2500

At one point we had P300 to 305 - engine misfire on all cylinders fault code but when we last cleared it it didn't come back.

Today we have tried the following based on reading this forum:

Cleaned MAF
Pulled all contacts, cleaned with contact cleaner and refitted
Checked vacuum pipes for leaks
Removed, cleaned and refitted crank position sensor earth bolt
Disconnected battery for 20 mins to reboot the ECU.

For info the battery keeps running flat so we suspect the alternator isnt charging properly but don't think this is connected with other issues.

Currently we have no fault codes showing but the engine still won't rev above 2500 and gets lumpy and dies when you try.

Any ideas what to try next?

Anyone know a good specialist in or near Birmingham who could come and have a look? (Car is not road legal so can't drive anywhere)

Many thanks

[Ardent]

Hello and welcome.

Have you checked the air filter?

Mr twos Willenhall?

[LozB]

Hello and welcome.

Have you checked the air filter?


Yep, used but fine, tried with it out too and no improvement.

Mr twos Willenhall?

Thanks, will google

[Joesson]

@LozB

Hello and welcome.
While my car will ( has since 2011) start on 6 month old fuel I doubt 2 year old fuel will have the same volatility, but then maybe you have made sure all is well in that department?
I have read of petrol filter blockage/ problem, so maybe worth a search .

[Carolyn]

In order of likelihood:

A bad MAF will not throw a code, but cleaning may have been insufficient.  The only way to know with the MAF is to put a known good one in.

If the alternator is dragging the voltage down, that could well be the problem.

You don't mention spark plugs or air filter, both things to consider.

Bad crank sensor.

Unlikely, but possible: Sometimes this can be a symptom of a blocked catalytic converter.  This can be caused by the break-up of the pre-cats in the exhaust manifold. It's worth removing the two oxygen sensors in the manifold and checking the condition of the matrix it should have a regular flat surface and the honeycomb should be easily visible.  If the matrix is worn, that could be your problem. 

[Joesson]

@Carolyn
It's sometime since I read about a blocked cat on here, but now you mention it the inability to rev was a typical symptom.

[Ardent]

I recall the same, but thought let's start at the cheap easy end 1st

[MRSwede]

+1 on the petrol filter and lines

[LozB]

@LozB

Hello and welcome.
While my car will ( has since 2011) start on 6 month old fuel I doubt 2 year old fuel will have the same volatility, but then maybe you have made sure all is well in that department?
I have read of petrol filter blockage/ problem, so maybe worth a search .

Thanks, hadn't thought about fuel but your are right it could well have been in there for a few years, will try that next.  Anyone know the best way to drain a fuel tank?

[Joesson]

Thanks, hadn't thought about fuel but your are right it could well have been in there for a few years, will try that next.  Anyone know the best way to drain a fuel tank?

I don't know the "best way" but a certain/ quick but not so tasty Way is with a length of tubing/ garden hose and a  suitably sized container/s  and syphon it out:
Hose long enough to reach the tank bottom at one end and the ground , or lower if possible at the other.
A good suck on the open end and then straight into the container on the ground, (the open end Must be lower than the tank end) just before you get a mouthful.
It is all in the timing. This probably should come with all sorts of health warnings, but I have survived several such procedures.

[LozB]

In order of likelihood:

A bad MAF will not throw a code, but cleaning may have been insufficient.  The only way to know with the MAF is to put a known good one in.

If the alternator is dragging the voltage down, that could well be the problem.

You don't mention spark plugs or air filter, both things to consider.

Bad crank sensor.

Unlikely, but possible: Sometimes this can be a symptom of a blocked catalytic converter.  This can be caused by the break-up of the pre-cats in the exhaust manifold. It's worth removing the two oxygen sensors in the manifold and checking the condition of the matrix it should have a regular flat surface and the honeycomb should be easily visible.  If the matrix is worn, that could be your problem. 

MAF - interesting comment - had assume no code meant it was ok - engine dies when we pull connector so it's definitely communicating with ecu - might give this a try after fuel check as new ones seem quite pricey

Alternator - interesting comment too, hadn't thought of that - problem still occurs when battery is fully charged though - does this mean less likely?

Plugs and coils done by previous owner, look new.

Air filter is ok, even tried without it installed and problem still occurs so can't be that.

Crank sensor - we checked the earth which is ok, again assumed faulty sensor would throw a code but maybe not? Do you need to remove oil to remove sensor? Does it just pull out once screw removed?

CAT - will check via o2 sensor holes. Currently struggling to remove heat shield due to bolt corrosion. Disk cutter in the post.

Thanks for all your advice

[Carolyn]

You don't need to drain the oil to remove the crank sensor. You're right about how it comes out.

The maf might be working-ish, but not well enough.

The alternator not working is a common cause of failure to rev.  This cropped up with another member fairly recently.  As it's bad, you have to replace it anyway.  If it's dragging the voltage down, sparks can struggle even if the battery has been charged.  The more I think about it, I'm thinking this is the most likely culprit, as we know it's malfunctioning. 

Fuel filter and pump problems are unusual.

[Ardent]

CAT - will check via o2 sensor holes. Currently struggling to remove heat shield due to bolt corrosion. Disk cutter in the post.

Don't confuse pre cats with actual cat.
Don't need to remove heat shields to check pre cats.

[Joesson]

Don't confuse pre cats with actual cat.
Don't need to remove heat shields to check pre cats.

But do really need a special cut away socket spanner to remove the sensors while the heat shields is in place/ or not.

[McMr2]

MAF - interesting comment - had assume no code meant it was ok - engine dies when we pull connector so it's definitely communicating with ecu - might give this a try after fuel check as new ones seem quite pricey

Alternator - interesting comment too, hadn't thought of that - problem still occurs when battery is fully charged though - does this mean less likely?

Plugs and coils done by previous owner, look new.

Air filter is ok, even tried without it installed and problem still occurs so can't be that.

Crank sensor - we checked the earth which is ok, again assumed faulty sensor would throw a code but maybe not? Do you need to remove oil to remove sensor? Does it just pull out once screw removed?

CAT - will check via o2 sensor holes. Currently struggling to remove heat shield due to bolt corrosion. Disk cutter in the post.

Thanks for all your advice

Had a bad crank sensor on a VW 1.8t once, no codes but same symptoms in that it refused to rev past 2500rpm or so.

[Gaz mr-s]

Just in case, - MAF cleaning, the sensor is not the easily-visible blob, - it's up inside the plastics.

[Ardent]

Spray, don't touch.

[LozB]

Ok today's latest update.......

First we tried running the engine with battery fully charged.  Still wouldn't rev past 2500.

Then we removed as much fuel as we could but not much as tank was almost empty.  Added 20 litres of shell's finest and ran for 20 mins and still no improvement

Then we fitted a replacement MAF out of a working Toyota, still no improvement

We have now removed the alternator ready to replace next weekend

Also started to remove crank position sensor, removed sensor itself and bracket holding wiring in place, but currently struggling to work out how to get to the connector on the other end of the wire - the cable seems to disappear above the AC compressor/fuel pump (not sure which it is) and can't see it or get to it. Any ideas what I need to remove to get to the connector?

Current plan is to fit recon alternator and new crank position sensor next weekend. Also check the o2 sensor holes for pre cat degradation - sensor removal tool in the post.

If all that doesn't work then we are pretty much stumped and will have to phone a friend at a local MR2 specialist.

Unless you lot have any other thoughts or advice?

[Ardent]

Still leaves the blocked cat option.

Never done it myself, but does the crank sensor not just unplug from the wiring.

[Carolyn]

The wire for the connector you seek is clipped to a small bracket on the dip-tube.  It is, as you suggest above the A/C compressor. (The fuel pump resides inside the tank).  My money is still on the alternator.

[McMr2]

Ok today's latest update.......

First we tried running the engine with battery fully charged.  Still wouldn't rev past 2500.

Then we removed as much fuel as we could but not much as tank was almost empty.  Added 20 litres of shell's finest and ran for 20 mins and still no improvement

Then we fitted a replacement MAF out of a working Toyota, still no improvement

We have now removed the alternator ready to replace next weekend

Also started to remove crank position sensor, removed sensor itself and bracket holding wiring in place, but currently struggling to work out how to get to the connector on the other end of the wire - the cable seems to disappear above the AC compressor/fuel pump (not sure which it is) and can't see it or get to it. Any ideas what I need to remove to get to the connector?

Current plan is to fit recon alternator and new crank position sensor next weekend. Also check the o2 sensor holes for pre cat degradation - sensor removal tool in the post.

If all that doesn't work then we are pretty much stumped and will have to phone a friend at a local MR2 specialist.

Unless you lot have any other thoughts or advice?

Hope you get to the bottom of it. These kind of problems are frustrating in the extreme and often due to something simple.

This is a proper hail Mary, but is the throttle fully opening? It seems highly unlikely but just thinking if the cable is reeeeeeally stretched or has become dislocated it might mean the throttle isn't fully open even if the pedal is flat to the floor. Easy to check by opening the throttle by hand?

[jvanzyl]

How tight is the throttle cable? It would be amusing (in a way) if it's a case of the throttle cable being too slack...

[LozB]

Thanks for responses again folks. You are brilliant.

Re the throttle cable I'm 99% sure it's not that as I rev by manually rotating the actuator on the throttle body. Good thought tho.

It's really strange, initially the revs rise but then once you get to a certain point the revs flatline and the more you open the throttle the more lumpy it gets.  It's like the air volume is increasing but the fuel volume isn't......or vice versa.

Crank sensor and alternator next weekend along with inspection of pre cat.

As a matter of interest whilst thinking about sensors do you think it's worth changing the camshaft position sensor at the same time? Do these ever fail without a fault code?

Thanks

[MRSwede]

Sorry naggin about fuel. Fuel pressure ?

I don't now if Gasoline cars work's the same way as Diesel.
Correct me if i am wrong (Wife say's it happens time to time)
Driving one of our diesel car's it was as if you turned of the key over 2000rpm when the fuel filter was clogged. Computer "shuts off" to save the engine when the amount of fuel isn't enough. 

[Carolyn]

Thanks for responses again folks. You are brilliant.

Re the throttle cable I'm 99% sure it's not that as I rev by manually rotating the actuator on the throttle body. Good thought tho.

It's really strange, initially the revs rise but then once you get to a certain point the revs flatline and the more you open the throttle the more lumpy it gets.  It's like the air volume is increasing but the fuel volume isn't......or vice versa.

Crank sensor and alternator next weekend along with inspection of pre cat.

As a matter of interest whilst thinking about sensors do you think it's worth changing the camshaft position sensor at the same time? Do these ever fail without a fault code?

Thanks

If you change too many variables at the same time, you risk learning nothing useful,  Get the alternator and crank sensor done (seeing as you've already spent that money) and see what gives.  I bet it will run fine.