THE ROVER SD1 FORUM

ramon alban · Posted: Tue Oct 16, 2007 10:10 am Post subject:

tommosredone wrote:

Hi Matt,
Are you saying that you start the car, and with no throttle pedal movement, the engine races up to 5000 rpm on it's own?
That would indicate to me throttle cable/spindle/disc problems...
If you are not touching the throttle, there could be no way the engine could get enough air to reach 5000rpm on it's own.
Lets have some more info on this!
Good luck!

Tom, In a different universe would the following scenario be possible.

The cold start injector gives a good squirt of petrol and a massive rogue air leak into the plenum provides enough air to generate a combustible mixture so the engine fires and runs flat out until it is stopped by a completely kyboshed mixture due to that massive air leak (somewhere)?

Matt. You mentioned the overrun valve.

Well it lets air into the plenum from the air rail when manifold vacuum is high to generate a combustible mixture on overrun when the fuel condensed on the inside of the plenum evaporates under the influence of the vacuum, so that same unburned fuel cannot not pass into the exhaust system where it will detonate with the air there causings lots of banging and heat.

Now this valve can get stuck open or closed, either way its a problem so I suggest you take it off, clean and inspect and put it back with all tubes intact.

It is mentioned on page 4 of the PDF available here:

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but if that is not the cause you need to review all the Air Leak test procedures in the same PDF because something is making your engine run flat out momentarily and that can only be a combustible mixture that lasts ONLY for that same period of time.

Another big orifice that must be a suspect, the brake vacuum line which should have two one way valves one in the plenum and one on the servo.

_________________
Ramon

Mattv8 · SD1 User Joined: 20 Sep 2007 Posts: 28

Hi Tom, Ramon.

Ok more info.

The car will not start without opening the throttle a little. then it revs round to 4500-5000 rmp where it stayes for a second or 2 before decelerating to stall.

if the throttle is re-opened befor the engine drops below 1500 then it races again to 4500-5000 rpm. this is with the tinyest ammont of throttle.

The cold start injector is disconnected.

Is it the TP or the AFM that tells the ECU when and how long to fire the injectors for?

The engine will not start without opening the throttle... WHY???

ramon alban · Posted: Thu Oct 18, 2007 11:46 pm Post subject:

Mattv8 wrote:

Hi Tom, Ramon.

Ok more info.

The car will not start without opening the throttle a little. then it revs round to 4500-5000 rmp where it stayes for a second or 2 before decelerating to stall.

if the throttle is re-opened befor the engine drops below 1500 then it races again to 4500-5000 rpm. this is with the tinyest ammont of throttle.

The cold start injector is disconnected.

Is it the TP or the AFM that tells the ECU when and how long to fire the injectors for?

The engine will not start without opening the throttle... WHY???

Hello Matt, My prior suggestion was more a hypothetical response to Tom who posed a question regarding the requirement for the engine needing AIR. And therefor I postulated a couple of possible entry points IF the CS injector was connected.

What I cannot yet grasp is how many if any of the following possibilities have been eliminated.

Chris Powell explained that a NOISY throttle pot can cause probs. If it is not connected then that is one issue and the car MAY not run in that situation. If it is connected a prior report indicated that there was a noisy pot. Is it fixed or replaced? just taking out of circuit is not a solution.

I have suggested that the Overrun valve may be jammed open. If its open then this allows loads of metered air into the plenum which would also bring in fuel as determined by the action of the AFM. Have you checked to see what the status of the overrun valve is?

I have suggested that airleaks can really upset the system. This is tricky because the only diagnostic method is to check for air leaks with the engine idling. In your case this is not possible so one would have to modify the procedures to make a thorough physical inspection of all pipes and then disconnect everything that is not needed (ie brake servo, Overrun valve and other possibilities)mentioned in my Plenum essay) and try to get the engine to start without them.

You said that the fuel pressure fell a few PSI when the pump stopped. Has that situation been eliminated - if not then fuel is going somewhere, possibly into the manifold and causing some sort of uncontrolled ignition.

You confirm the cold start injector is disconnected. Does that mean electrically disconnected? OR removed from the plenum and the orifice blocked up with sticky tape or similar???.Its got to be removed to eliminate any leaking

You ask what determines how long the injectors are open. Well its mainly the AFM, but with minor adjustments from air and coolant temp sensors, and battery voltage.

Note, this brings me to an observation. My last point, particularly and several others already made here or elsewhere, are answering questions that are FULLY explained on my website, sometimes in excruciating detail. The fact that you are still asking some of these questions makes me think that some suggested reading matter is not being well understood. If so, all I can suggest is to re-review all the articles related to the Efi components.

You ask why the engine will not start without opening the throttle. Well under normal circumstances it should - but one reason why it might not would be a blocked idle gallery and breather gallery. This came up previously and the only way I know of to do this is to remove the plenum and poke out the crud. I dont remember if you did this?

One thing that keeps occuring to me is that there may be a fundamental error in the wiring and/or the way things are connected.

If that were a problem, I cant think of any way of telling without doing a point to point check on the whole wiring loom.

Another thought is that the engine seems to start but will not keep running this may be due to the Steering module and the way it drives the main and fuel pump relays and how the fuel pump contacts in the AFM are working.

I have this week, added a new article on the Efi (Diode) Steering Module and the main and fuel pump relays which explains how and when those components function.

_________________
Ramon