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MG MGF Technical - MGF 1.8 mpi Starts and idles but won't rev up

Help wanted!.
My F will start on the first crank of the starter and idle happily, but when you open the throttle it won't rev up.
The engine induction noise roars but the engine will go no further than 1500ish rpm. it misfires and dies.

When it first starts it sounds rich with a rhythmic note in the idle and when it warms up it cuts out and won't start again 'til its cool.
I've changed the ECU temp. sender and the dis. cap and rotor arm and the ign. leads.
Cleaned the crank sensor, The mag. tip was covered in small particles, but no change when clean.
Checked all fuses and connectors.
The fuel pump delivers plenty of fuel on prime before starting and I've changed the filter, had the injectors cleaned and serviced and checked the pressure reg.
All seems OK.
I'm stumped, the car is unusable.
Has anyone had similar before ?, all help appreciated.


N HUGHES

Yes, I had a very similar sounding problem with my 1.8 mpi - Ran on idle but would not pick up and would stall if too much throttle was applied. I read that coil related problems tend to become more apparent when the engine is warm and the coil breaks down. I replaced my coil but it wasn't the cause of the problem. The leads/rota arm/dissy cap/plugs initially worked for me but I kept getting a re-occurring intermittent fault which appeared to be cured by an overnight charge of the battery?? - Tests showed that my alternator wasn't giving out the correct output, so that was changed - but the problem came back again after a short time - Then the battery was tested and found to have a dead cell - that was changed but again the problem came back after initially working fine - but this time I could not start the car on the key, not enough power to starter motor but battery was fine and the car would bump start.... FINALLY, while testing the starter cable and the various earth connections back to the battery I found that the engine earth to body connection (directly under the open boot vent) had a high resistence reading - I undid this, cleaned the connection and the screw thread with contact spray and problem solved!! (or so it would appear.... six weeks, no re-occurrence, although this may be just another coincidence). It may have no bearing on your problem and I'm not entirely convinced that a poor earth could be the cause but I thought it was worth a mention.
Mark

Mark,
Thanks for the suggestion, It didn't do the trick but it was dirty and needed doing & just the kind of thing that's likely to be the answer.
I had a scimitar many years ago that suddenly worked properly when a jump lead was put between the engine block and the battery -ve, because the earth return was defective.
Good idea, but no coconut, sadly.

Any other ideas out there ?
N HUGHES

I think a thread reported a similar problem a while back cleared with new plugs - the old ones worked but the gap was too large or the insulation was breaking down at higher frequency or some such. It can't do any harm, although a b***** to get at.
Charles

Check the TPS and the3 wires from the TPS back to the ECU.

Regards,

Simon
SCJ Connolly

Thanks for the contributions, chaps,
I've changed the plugs and done the Throttle Pos sensor, previously.
I'm going to take off the ECU and look for dirty contacts and check the relays behind, tonight.

I'm also wading through the MG-Rover.org forum in my spare time.

But don't be put off, Keep them coming. The answer's there somewhere.
N HUGHES

I currently have exactly the same problem on a 1.8 Freelander. Identical engine. The crazy part of this is that I have a MGF sitting next to it on the driveway and have been swapping parts to try find the answer, but so far no luck.

My car will run until warm and then will refuse to rev up. If you cut it at that point you will battle to start it again. if it starts it simply won't rev up. If you leave it idling, it eventually worsens and dies. Let it cool a bit and it all goes fine again. The car is in fact driveable for 20 min till it is warm again and the same problem re-occurs.

I had a vary similar problem on my Alfa, which turned out to be the crank sensor - It would work when cool but when warm would go faulty.

My Freelander has me stumped right now - I swapped the Crank sensor mith that from my MGF - no joy.

I have still to swap the coil - if I can get it loose, and I am wondering whether the fault could possibly lie with the throttle sensor?

To me it really seems like an ignition problem but I am beginning to think that the computer is not fueling the car properly due to an incorrect reading from one of the (Throttle?) sensors.

Have you made any progress?
Tom
Thomas Schonen

Update - I spent a good few hours yesterday swapping over bits from the MGF to the Freelander. I got the coil loose only to find the connector marginally different and incompatible, so I carried on with the rest. Surprisingly I swapped over the ECU and the car fired up as before with the same problem still. The MGF fired up and ran fine with the Freelander ECU, so I was thankfully able to rule that out.

Next I dismounted the whole inlet manifold plus fuel rail and injectors, only to find I could not get the damn thing out of the MGF, being mid mounted. Instead I just swapped over the throttle ass. and the injectors, and whatever green sensor it is in the inlet manifold.

Unfortunately the problem persists, and the MGF still fires up and runs first time. By now I have replaced practically all parts! The only two things that remain are the ignition coil and the possibility of fuel pressure. So today I bought a coil. Will post a note when I have installed it! I think I have fuel pressure, because when it runs it runs fine - I must have another listen and make sure actually. The problem is too predictable to be a blockage and it only happens when the engine is warm - all things now point to the coil breaking down, but funny enough, there is a strong healty spark at all times.

Tom
Tom

Tom,
Thanks for all the input, it sounds like you have the identical problem.
You have my full sympathy.
I, sadly, haven't cracked it yet. I'm waiting for the ECU to come back from testing.
It passed with no fault found, bizarrely, I was hoping they'd come back with bad news about the fuelling circuits, oh please, and that a repair would sort it.
It would have meant an end to the pain.
In forty odd years of playing with cars & bikes this has to be the worst fault I've had to fix.
.... & .....
The only vague consolation is that I've learned lots about the fuel injection etc. and I have more idea than the garages locally.

Re: the fuel rail, I did manage to get that and the injectors out on their own, I had to remove the Stepper motor to get at the screws, but it will come out on its own if you persist.
Tight but do-able.
I had the injectors cleaned , back flushed and new seals, but the guy said there was nothing much wrong with them.

I'm waiting for the ECU to come back and then I want to start the car up and crack the exhaust open in front of the cat. I've heard reports of blocked cats doing similar to this, too much back pressure in the exhaust ?, who knows.
After that there is probably only the harness in the back end.
Thanks for posting, if anything happens I'll be sure to let you know, you'll hear the yell if nothing else.

Gramh
N HUGHES

HI,
Have you checked for a partially blocked fuel filter?
Could be your problem.
willyphixitt.
W A Nixson

I don't know if this helps, but I had a similar problem in a mini I owned many years ago.

It had a similar problem that took me weeks to find.

It would start and idle ok but as soon as you tried to up the revs it cut out and died.

It would start again with out problem, and I found it was a broken wire in the LT side of the coil.

When you reved the engine or tried to drive away the engine moved slightly on its rubber mountings as it either revved or took up the strain of moving forward against the torque of the wheels.

As the coil was attached to the engine this moved the attached 12v wires and unknown to me there was a break in the wire under the pvc covering, so the slight movement moved the copper wire under the pvc slightly and broke the circuit causing the spark to fail and the engine cut out. When it cut out the engine moved back into position and the wire relaxed bridging the gap, and making the circuit again.

It was a nightmare to find, after I had replaced points, plugs, coil, cap, etc, but the immediate cut out told me electrical rather than fuel or other.

Don't know if this helps at all, but you have my sympathy as it was weeks before I found this fault.

Brian
Brian

Dissapointment...

I have swapped absolutely everything, from the MG eventually - except the coil - it didn't fit. The new one arrived on Tuesday - it was the only thing left. Put it in - went for a couple of drives, and Great things looked good! It did struggle to start a bit though as before. Then yesterday after a 30 min Drive it died with the same symptoms. absolutely no difference with the new coil. I am absolutely mystified!
Thomas

Does your ecu assembly (the one at the rear left of the engine bay) have the MAP sensor in it? If so did you clean it?

Branko

After staring at this thing for a while I went back to basics. Air, Fuel and Spark. Led me to think about the advancing mechanism that the older cars had, but I couldn't really get anywhere with that.

I started thinking Fuel starvation. So with the car in a "Broken Down" condition, I removed the left bolt from the injector fuel rail (The right one is under the Stepper motor - I just left that one), and I popped the left injectors out of their manifold sockets. Then went and started up the car, and yeah - it actually started and sputtered along, and I could see little jets of fuel spraying across the gap and into the orifice in the manifold. Trying to rev the engine would normally cut it out anyway so no luck with that, but it appeared to be fuelling. Put it back together.

Went away for a while and came back later. Car started normally and was idling and revving fine. I decided to repeat the previous experiment, so I popped off the rail with the engine running this time, and was initially surprised by the response - the engine ran away and revved up wildly - makes sense when you think about it - you are drawing in false air, bypassing the butterfly and essentially running with a full throttle! With this happening the volume of fuel coming out of the injectors incread substantially - it becomes a pretty solid gush!

I have since SOLVED THE PROBLEM! (I hope I havenít posted this prematurely!! but the car is running and I did quite a few runs with it till the early hours of this morning) The problem is NOT heat. It is TIME. Nixson (above) hit the nail on the head as well. You are not able to sustain the required pressure in the fuel rail. When the car stands, enough fuel gets through the filter and perhaps enough dirt falls off the fuel filter to run for a while till you pick it all up again and your fuel pressure collapses.

In the Freelander - access to the pump is easy - the tricky bit is getting the retaining ring off, but fortunately I had a gizmo lying around from when I took apart my Alfa because of a stuck gauge. Anyway, managed to get the bugger out and it is a bit messy with fuel all over - best not to be paranoid at this point! I was checking for a built in filter in the fuel pump. The actual pump housing is predominantly plastic. It has a very course outer filter which appeared fine. There are three clips holding the bottom cover onto the housing - pop it open and you find a really fine flat "Envelope" looking filter on the bottom of the intake. This filter was black with dirt -really fine, best described as silt. Pretty sludged up - I was onto something! Took it inside - had a good brush at it with a paint brush and it changed back to its normal translucent colour. The whole pump overhaul took under an hour till it was back in place with the car running. It also starts quicker now. All kinda makes good sense! One of the most perplexing problems I have faced in 20 years of tinkering with cars and bike. I enjoyed the callenge but hell was it frustrating to have a non runner!

Huges - I know you said you played with the fueling system, had the injectors cleaned, etc - Have you tried cleaning out the fuel pump filter?

Best of luck!
Tom
Thomas

Hi Tom,
I thought I was on the right track from what was posted earlier. Hopefully Mr Hughes' problem is the same. You may have filled up with some dirty fuel recently to add to your woes.

The fuel filter should be changed every 60,000 miles.

Good luck.
willyphixitt
W A Nixson

Hi have seen many similer problems to this try wiggling the wires next to the crank sensor when reving car I have seen on many occasions the wiring worn near to the sensors regards ex mg tech
ex mg tech

Tom, Great news.
I never did manage to get the fuel pump out, but had changed the in-line cartridge filter, as you say it had black sludge in it. That prompted the injector clean. I'll go back to the pump again.

The ECU came back with no fault, so continued trying.
In fact things are worse,now the car will crank OK but the fuel pump does not prime up at switch on and does not start. There is an audible two tone beep at ignition switch on which used not to be there.....
so I had a look at the black relay box innards, looking for a fuel pump relay problem maybe, there are four relays in there one of which was quite badly burned at the points, so i've cleaned it up gently and put it back together. No change though.

I'm borrowing a trailer and taking it to Barbers, the ex MG dealers mid week, they still have all the diag kit and are willing to run it on the kit for £50 and see what comes out.
I'm extremely pleased you've got your's working again and i'd be lying if I said I'm not envious, well done.

Thanks to all for the posts, I'm trying them all.
Gramh
N HUGHES

Latest situation.
Severely depressed after last post. Bottle of red and curry revived spirits, though.
Sunday.
Removed the fuel pump (swine of a job without the tool) and checked the little gauze bag filter at the bottom, nothing much on it. While the pump was out ran it with a clear pipe to connect the output and return and watched the fuel going round. everything OK. sounds OK too.
The main in-line filter is new and I change them every 20K or so.
Started looking for duff electrics, revisiting Mark's earlier suggestion but more aggresively this time.
Replaced the ignition coil unit - no change.
cleaned up the multi junction earth box by the fuel cut off, also checked conductivity & function of fuel cutoff switch, all OK.
Redid the body earth in the engine bay.
Once started again it seemed a little better, so Before it goes on the diag m/c I'm going to try a new Crank sensor. It has been checked and pronounced OK along with the TPS, but where else can i go ?.
To Ex MG tech & Brian, thanks, I tried the wires.
To WillyPhixit and Tom thanks, I don't think the fuel system could be much cleaner now.
Thanks to all.
N HUGHES

HI Mr Hughes,
What engine management system has your car got. There are several out there. It depends on the year of the car. Mine is a MPi MEMS 1.9, a 1996 F MPi (up to 200MY) This has the MAP sensor in the ECU itself. One of the sensors is not giving the right info to the ECU and it makes the car run in "emergency mode", ie you can just limp home with it. You've checked the crankshaft sensor but there are 7 basic sensor inputs to the ECU. Have you cleaned the MAP sensor. If you have a VVC, then there is a cam sensor also. What about fuses have you physically checked each one with a multimeter (back to basics and all that)? What year and model of car do you own? VVC or MPi?
Hope I can still throw some light on it after all the trials and tribulations.
Regards.
Bill
aka willyphixitt
W A Nixson

This weekend I swapped the Crank sensor and the Throttle sensor - no change - and checked the MAP sensor & pipework, no change.
The MAP sensor is onboard the ECU ( a MEMS 1.9 MPI), connected to the right of the manifold via a tortuous pipe and a plenum box. No fractures, no punctures, some chafe though.
The fuses are all ok and voltages good.
If you disconnect the MAP at the ECU the engine goes really rough and dies, so it's obviously working.

Willy, I know what you mean but this joker couldn't 'limp home' if it tried, it dies when it warms up. takes about 2 mins.
It looks and feels like it's still in the startup programme the ECU has - which richens the mixture to start and has a fixed ignition setting.
When it warms up it's too rich and the engine slows , roughens and dies.
It doesn't read the TPS to tell it to adjust the mixture.
Having read the Manual I saw a bit that said once it is running over 400 rpm the ECU starts to look at the engine sensors to function, particularly the TPS.
I don't think were getting that over 400 rpm signal through, but if it's not the crank sensor that sends it, I don't know what would, If the crank sensor wasn't working the engine wouldn't be able to start..., and it's a new one.
The ECU should read it and that's been checked and found fault free.
If it was duff wiring between CKP and ECU it wouldn't be able to start, because it couldn't time the spark.
If it was duff wiring between TPS and ECU it would get over 400 rpm and then look at the throttle setting and either die (no signal) or idle (no variation) and steadily warm up.

I'm still stumped,
Regards,
Gramh ( aka N Hughes )
N HUGHES

Hi Gramh,
Sorry to hear that any of the suggestions from everyone has not produced an answer to date. Thinking again, as the fault occurs when it's warmed up, there could be a fault with the coolant circulation. The thermostat or the jiggle valve could be screwing things up. You could try running the engine with the pressure cap removed from the overflow tank to see if there is any difference. While in warm-up mode the coolant only circulates around the engine allowing the alloy engine case to evenly warm up. Have you noticed the temperature gauge when the engine dies? Maybe not as your head was probably stuck inside the engine compartment at the time. As you have been through all other suspects (twice at least in most cases), I can only suggest the thermostat and/or jiggle valve may not be functioning as they should. The thermostat is then not sending the message to the ECU that the engine has now warmed up and the ECU in turn to lean the fuel.
Keep your spirits up. The answer has to be somewhere.
Good luck.
willyphixitt (no not yet)
W A Nixson

Hi, I forgot to say that the thermostat and the engine coolant temperature sensor are two separate items so check both for correct functioning. You also have the idle air control valve and its stepper motor to investigate if you have not already done so.
I also assume that you somehow or another have not got a blockage in the air intake system. Temporarily remove the air filter and leave off the filter box lid to see if there is any difference during the crucial few minutes.
Good luck.
willyphxitt (this time I hope)
W A Nixson

Willy,
thanks for the thoughts, you're right they're all possibles - I think I've checked them all once or even twice so far, maybe more in my sleep.
Since last post I haven't had a decent evening to get at the car since the w/e. Rain biggest problem.
My next job is going to be releasing the exhaust manifold to check the cat blockage theory. It shouldn't take too long.
I'll post again when I've done it.

Regards,
Gramh
N HUGHES

Is there abyway you could 'simulate' the sensor readings ?

So you could then test out the 'not getting temperature' settings theory, where as you say its needing to then say "now switch to lean mixture".

If you know what the voltage/resistance settings should be from a friends working MG, from the temp sensors then you could build that, and then switch this simulator in, and see if this keeps the engine running ?

Best of Luck

Brian
Brian


Gramh,

This website may help you

http://homepage.hispeed.ch/TomsSeven/Navigation2/Map.htm
Map.gif

Regards,

Simon
SCJ Connolly

AT LAST,
I slackened the exhaust manifold to test the blocked cat idea and release any possible overpressure and BINGO the engine starts to rev up again straight away.
Noisy mind you, but healthy.
Instant improvement.

It's always the last thing you try that works..., but that's because you could feel the exhaust gases and even the firing rhythm still coming through the tailpipes, but it's blocked enough to stop the engine revving up.

So, it's a new cat, some new tyres and an MOT, It should go like new again with the amount of new sensors and parts that've been put on it in the meantime.

Thanks to all for all the suggestions and help and moral support along the way, and I don't forget the website provider - It's really useful to have this forum, well done.

Best Regards to all.
Gramh.
N HUGHES

Great to hear you are all sorted.
willyphixitt (yes indeedee)
W A Nixson

Gramh,

Great news - I've been following your thread with interest - Always nice to read a happy ending!!

Funny thing though - Went out for tea on Saturday night to a friend's house and he said "I know someone with a car like yours who's having problems..." after a few minutes I realised I'd been following the story and that it was you he was talking about! (and that I'd contributed to the thread way back in June... albeit unsuccessfully). Clint said he thought it might be the cat but I knew you were going to try it at the weekend anyway - Great result.

I recently upgraded my exhaust and had to replace the cat at the same time (as the old cat was fused to the silencer section (reasonably okay to disconnect from the other side though - after a good soaking with penetrating spray).

Anyway, just thought I'd post to say I found a really good deal on ebay - The same cat used on the MGF is used on other Rover 1.8 cars, so I searched under Rover, rather then MGF and found a new one for £37.00 (cheaper than the MGF version but exactly the same part number and even specified MGF in the list of comparable cars).

Mark
Mark Clayton

This thread was discussed between 30/06/2008 and 18/08/2008

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