38 replies to this topic

[a13gpn]

Hello, Bit of advice needed really.

Getting a quite famous MPI Rally Car running again after a good 7 years since proper running. The engine now turns over and fires and runs ok.

However I am having some quite strange problems it still isn't 100%.

- The engine is running very Rich, Black soot around the exhaust after you rev up 3k+ also seems to be spitting black soot out as well. 

 

- Engine idles ok around 900. And revs up fine if you take it very very slowly. 

 

- Main problem is, when you push the throttle quickly the revs immediately drop to 0 and the car fights a stall. If you release the throttle immediately it usually recovers but if you hold the throttle down it stalls.

 

- The car isn't very drivable because obviously when you push the throttle down the revs drop immediately and it is very lumpy.

- No smoke white or black.

 

- I have changed the Coolant Temp Sensor and Checked Earths.

 

- Brand new Racing Spec battery.

 

- Runs an aftermarket MBE Engine management system.

 

What are the next things to try to get this running smoothly?

 

Thanks

 

[Fast Ivan]

is it otherwise using the standard MPI set up, injectors, inlet manifold, sensors etc?

Does it still have the OBD comunication port?

[a13gpn]

Yes standard setup sensors wise, but with a 52mm Throttle body and K&N filter. 

It doesn't have the OBD comms port but does have another serial connection into the ECU which I am trying to get the correct cable for.

 

It has stood in a barn for many years before I got it, maybe something has perished/corroded? 

[Fast Ivan]

could be a number of things and the running rich may not be related to the rev issue.

I would start with a good service, including flushing out the coolant system.

Check the valve clearances, and I would be doing a compression test as well, just to give an indication of the general health of the engine.

It could be something as simple as the spark gaps or a blocked air filter, or if the cooling system is clogged up the CTS might not be able to read correctly.

After this I would check and clean all of the sensors and connectors, make sure they aren't corroded and are seated correctly. Check the loom for damage and scuffing leading to exposed wires.

Does it have an adjustable fule pressure regulator fitted? this could be causing an overfueling issue, worth checking for sure, maybe back it off a bit.

An injector stuck open would also cause over fueling though normally they become bocked and reduce flow.

In terms of the ECU and diagnosis, the reving issue sounds like the throttle position sensor or the throttle switch.

the runing rich could be linked to the MAP sensor /or the IAT sensor, both of these are used to calculate the volume of air present and then the fueling is adjusted to suit.

A faulty lambda might also cause problems.

A diagnostics reader may through up more information, remember that it may well highlight error codes but you will also need to look at the live data and compare that to the factory spec.

Hope this helps

Edited by Rob Mac, 02 November 2013 - 09:34 AM.

[a13gpn]

Ok spent a few hours on this today.

Checked all Sensor connections - All ok with no corrosion.

Removed, cleaned and replaced all Earth connections again.

Removed, cleaned and replaced all Spark plugs (gaps look around 8mm?) - note they were absolutely covered in black soot and they were brand new a month ago.

Tried a number of other things but the problem still persists, engine ticks over ok, but when pressing accelerator the engine begins to stall and rev counter drops to 0. Note if you absolutely floor it, it won't stall and seems ok but obviously not running correctly in the lower power band. 

At the same time as pressing accelerator hard you get a spray of black soot out of the exhaust.

If you listen in the engine bay when it is "stalling" the problem seems to be coming from the throttle body area, and sometimes you get a hint that air might be escaping from the throttle body area, where would be wise to check for leaks? Could this be causing such a problem?

 

Another possibility was when first trying to get the car started the Main Engine relay was covered in corrosion, cleaned up and the car starts ok, but on one occasion some sparking and smoke came from the box, could it be that 1 of the other relays in this box has shorted out and causing this? I believe the lambda sensor heater is controlled from here? 

 

Any more ideas? This is a really famous car and would love to get it back on the road again.
Cheers

Edited by a13gpn, 02 November 2013 - 06:52 PM.

[Fast Ivan]

the lambda relay is in the main relay box, top left of the engine bay

do you mean 0.8mm spark plug gap?

[cian]

Id say its overfuelling with the black sooty plugs and black smoke out the exhaust, turn the furl pressure down on the regulator that will lean the mixture

[a13gpn]

Yes sorry 0.8mm gap but this is only a rough estimate, they are brand new correct spec plugs but I haven't gapped or adjusted them. Just fitted to get it running, what should they be set at?

I would agree that it sounds like an over fuelling issue for the soot etc but I still have the stalling after pushing throttle issue and I think the two maybe combined.

The car does not have a fuel pressure regulator fitted, standard pump in the tank, braided hoses through the inside of the car straight to the throttle body.

[Andy500]

There will be a regulator fitted, is it using the standard mpi rail with the regulator in the end? This is non adjustable anyway unless you crimp it.

 

Have you checked the return fuel line isn't being squashed/squeezed anywhere as that would cause the pressure to increase and then lead to overfueling.

 

Have you had a code reader on it?

[cian]

Definatly get the laptop hooked up to the ecu and take it to a pro because it sounds like something in the brain needs adjusted

[a13gpn]

Ok! So little update.

I have made a cable and now have the car connected up to Live ECU mapping/diagnostics. My results are the following.

Coolant Sensor - All good.
Air Temp Sensor - All good after a clean.
Throttle position Sensor - All good.
Battery volts - All good around 13v.
Lambda Sensor - getting a signal back but it rapidly from 0v-1v totally fluctuating randomly. Then after the car is warmed up it drops to 0.3,0.2,0.1 then dies totally. (The car keeps running) 

From this I seem to think that I must have a problem with this sensor?

I am still getting tonnes of black soot out of the exhaust in a spray (coupled with dirty plugs), and a big hesitation when putting your foot down slowly. When you reach about 2500rpm it is fine but below this it seems like it is starved of fuel possibly, it seems to almost stall until you reach 2500rpm.

Any ideas on the next things to try in this investigation?

 

Cheers

Edited by a13gpn, 01 December 2013 - 11:51 PM.

[Badboytunes]

Sounds like its running rich, what it could be though I couldnt say.

[jaydee]

Try a new lambda sensor

[Fast Ivan]

the lambda readings are odd - the fluctuating is exactly how it should work, from lean to rich in milliseconds. but the dying when warm is odd but don't go splashing out just yet.

the sensors that you have checked, are they operating within the correct parameters from cold up to warm?

Does the throttle position sensor reading increase with revs?

do you have anything on the map sensor, the throttle switch?

did you do any of the suggestions I made in my first post? 

[Shep76S]

Cool, the Plant brothers car?