Engine running too fast and then stalling

[perkins_gl]

Hi All

 

I have swapped my exhaust including manifold for a sport exhaust and a K&n air filter for the std air filter. I also replaced the bosch fuel pump to revingtons pump and filter arrangement and replaced all the fuel tubing. I restarted the car today and it runs badly at 2500 + with no choke and tries to go faster but stutters and fails. I have disconnected the choke and taken off the air box and all the butterflies are closed. I have checked and retightened the manifold nuts to ensure no air leaks.

 

Is the air leak screw fully tightened low revs or fully open low revs I think its closed and this is how I have mine (probably cracked open 1/2 a turn). doesn't appear to be a great fit in the inlet manifold but still not bad. so please send me any ideas to stop me pulling out what's left of my hair.

 

Cheers George

[Richard Crawley]

George

The position of the air bleed screw is probably about right. They vary from car to car & the more you open the screw, the more air you let in behind the butterflies & so increase the tick over; if everything is in perfect condition & the butterflies are correctly synchronised you should just about be able to stall the engine by screwing it fully home; I doubt this is causing your problem.

 

There is a lot more to checking butterfly synchronisation than simply removing the air box & checking they are all closed, even the slightest variation will affect things; but this won’t be causing your problem at 2500 + revs either.

 

Was the car running OK before you did you changed things?

 

Are you sure it’s not electrical (timing!)?

 

Have you bled all the air from the system?

 

Have you installed the Bosch pump correctly & checked/reset the fuel line pressure?

 

Are all of the injectors firing OK?

 

Have you changed anything else?

[perkins_gl]

Hi Richard

 

Thanks for the reply.

 

The engine was running fine before I meddled, same old story.

 

I haven't physically checked the timing but it was running OK and I haven't touched the distributor so I'm guessing it shouldn't have changed.

 

As for air I have had the pump running for several minutes previously and it has recirculated petrol so I'm assuming (probably wrongly) that the air has cleared? Wouldn't air cause it to stutter and run poorly but not rev so hard?

 

I believe I have installed the pump correctly according to the instructions. I haven't reset the pressure as I have no way of measuring it. i have seen fuel pressure kits on ebay for £40 or so are they any good?

 

Not checked the injectors I assume (again) that i do this by pulling them out individually while the engine is running and check they are pulsing and giving a good spray? If so this is a little difficult as the car probably runs for 1 -2 mins max before stalling.

 

I ahve also replaced all the brak and clutch pipes including flexible hoses and as yet haven't refilled and bled the system.

 

So from what you've said I guess checking the pressure would be next on my list and the timing. Advice on checking for air in the system would be welcome.

 

Cheers George

[Laurie]

Hi George

 

Is she ticking over normally and won't go above 2500 or is she stuck at 2500?

 

If the former then air or dirt is probably upsetting the system and if the latter then, having had your manifolds off are you really sure that the butterflies are fully closed, with no air passing. The tiniest crack can give 2500.

 

I see no reason why your fuel pressure should have changed unless you were playing with the PRV. The PRV is only dependent upon its own set tension to relieve at a given pressure regardless of the output pressure of the new pump.

 

By the way, did you fit the system with the small glass pre - pump coarse filter?

 

You should be able to check all six injectors within 2 mins. Remove all retainers, start (they'll stay in due vacuum pressure)and pull 1 injector at a time. If spitting first try bleeding by holding vertically (spray upwards not downwards) and pull the pin on the end of the injector for a moment.

 

Regards

 

Laurie

[Richard Crawley]

George

Firstly check the ignition timing is set correctly & all the ignition components are in good condition - replace the lot as you will then be sure! & set up the excess fuel lever (choke) correctly. To have any chance of setting up the fuel system properly, you need to get yourself a pressure test gauge. You can get all the bits you need to make up a test kit from RS Components for between £30-£35, a search through the archive will reveal the details; I don’t know about the kits on E bay but I suspect that some enterprising fellow is buying the bits & then selling them on at a small profit!

 

Remove, strip & clean the PRV; reassemble & put it back on the car - count the number of turns when you dismantle the valve so you can reassemble it somewhere near to correct pressure.

 

Remove the M/U main inlet hose & check the small nylon filter is in place & not clogged with debris. To purge the system of air up to the M/U, loosely fit the hose &, using a piece of rag to catch the fuel, switch on the ignition for a short time so that fuel spurts from the hose; tighten the hose. Once you’ve done this, switch on the ignition & adjust the fuel line pressure to 105–108 PSI.

 

Remove the injectors & check the small nylon filter in the end is clear of debris (if they are still there as many recon units no longer have them fitted!). Take the spark plugs out & get someone to crank the engine in 20 second bursts (with 20 seconds rest in between) while you bleed each injector in turn by GENTLY just lifting the injector poppet valve off it’s seat; do this with your finger nails or a long nose pair of pliers; when fuel starts to spurt through the injector, move on the next one until you’ve purged all the injectors of air. Don’t crank the starter for too long without letting it cool down for a few minutes or you could cook the motor windings; do 2 injectors at a time & let it rest for 5 minutes.

 

Put the plugs back & the car should stat & run fairly easily although there will still be air working it’s way through the system into the injector lines & you will need to bleed these several times, individually before they fully purge of air.

 

Once the car is running nicely on all 6, re-check the fuel line pressure with the engine running; ideally it should be done with the car being driven “spiritedly” to see if the pump maintains line pressure but you will need more than the basic pressure test kit to do this (I don’t bother!).You need to maintain a reading of 103 PSI, minimum.

 

Lastly, if you still have problem, re-fit the standard air filter (there’s nothing wrong with the design anyway!); if it still don’t work after all that, you have another problem!

Edited July 10, 2006 by Richard CRawley

[JohnC]

Hi George,

You did re-set the butterflies after putting the inlet manifold back on, didn't you? If not, you haven't a snowball's chance of smooth idle/running. Just trying to not disturb the settings during removal/replacement won't cut it. Synchronising the butterflies is free, and requires no equipment, just patience and care. Richard (I think) favours the 'fag paper' approach, I favour the 'sensitive fingertip', but YMMV. Search through the forum if this doesn't make sense...

Regards,

John

[perkins_gl]

HI All

 

Thanks for all the information.

 

Laurie: its the car going straight to 2500+ and then trying to go even faster but stalling and failing.

 

John: No I didn't reset the butterflies I just hoped that it would all remain OK. Clearly not!!

 

Richard: The ignition stuff is fairly new went on in june 05 but the car was only used for one month before the diff seal started leaking and I took it off the road for a quick repair (ha ha).

 

I'll start by checking the ignition and resetting the butterflies if that doesn't do it I'll get the gear and check the line pressure. If that doesn't work I'll buy an MX5!!

 

Cheers George

[Red Leader]

Hello George,

First of all don't touch anything that you have not just changed ie the PRV or the Ignition system, as that should have no impact on the problemand may cause even more.

I would suggest that you reset the butterflies first, using a fairly inexpensive airflow gauge like the ones people use for balancing twin carbs.

Then bleed all the injectors in the way previously described. I air has got into the system it will take some time to get it all out. you may have to bleed it several times before you get it all out

regards

[Richard Crawley]

Laurie: its the car going straight to 2500+ and then trying to go even faster but stalling and failing.

 

John: No I didn't reset the butterflies I just hoped that it would all remain OK. Clearly not!!

 

George

It should have been obvious to me that in changing the exhaust manifold, you’d also need to remove the throttle bodies & the throttle linkage so that one went over my head! I would agree with John in that it’s almost certainly due to the throttle linkage & butterflies being way out of synchronisation – probably one pair is remaining partially open. There are several ways you can set them up, as John says I use a strip of Rizla fag paper! I don’t smoke but my dad did & part of his legacy was to leave me several packs of the things so I saved them for setting butterflies & ignition timing! Read the archive posts to decide which method suits you best!

[perkins_gl]

Butterflies it is.