Flat spot caused by 3.5lt really a 3.9lt?!

[ecodan]

Hi all,
Problem I'm having is my sons 88 Range Rover has a flat spot when you try to accelerate over 80kmph. Will happily cruise at 120kmph, kicks down when you floor it, but no real oomph and very slow to pick up.

Background... Car came running poorly as some ones restoration, worse still they bought it as someone's restoration. Good news, engine rebuilt (very clean, uses no oil or water runs very smooth, plugs good colour no blow by in intake etc), 5 new tyres, new bushes shocks, new paint, etc. bad news microtech ecu (ran crap till removed, advice from Dyno guys was universally to pull it out) with lots missing from under the bonnet, silly high lift on springs and chassis.

Other good news, came with donor car, so pulled out microtech, moved over loom and missing original components... Spent three days painstakingly testing all components as per manual, started first time and ran / runs smooth and powerful from stand still, up hills but slow pickup under hard acceleration at highway speed.

It's been suggested the engine (marked 3.5lt) might now be a 3.9lt..
Running the flapper style Efi, which I know might not provide enough fuel for a 3.9 if that's even the problem...

So, suggestions... Upgrade efi fuel power boost valve? http://www.v8engines.com/carbs-3.htm (Original tests with in rover specs with pressure gauge at ignition on).
Does this computer accept a wide band O2 sensor (neither car came with O2 sensors), will this make it provide more fuel?
New injectors?
Or something I've missed (tps is calibrated and seems to check out with multimeter as does air flow flapper unit)

Also fuel filter changed (twice as fuel pump was swaped)

Appreciate any thoughts!
Cheers,
Dan

[superquag]

Had a close look at the vacuum advance gizmo? they are prone to perforate and testing is relatively simple. - Take the hose off at the other end, suck strongly and use your tongue to 'seal' the hose end. Wait 30+ seconds and see if the vacuum 'disappears'.
It shouldn't.

Being a tiny bit OCD, I'd also suggest taking off the distributor cap and rotor button - VERY carefully /budget on a new one anyway! - and see if your sucking is actually moving the IGN 'advance' mechanism.
Good excuse to oil the dizzy shaft felt pad.:p

A future Ignition module upgrade from the Prince of Darkness (LUCAS) to the BOSCH BIM 024 is a good idea.

There is a FORD rotor button that can be substituted for the OEM one, the advantage being a wider 'business end electrode'. Rover v8's can be run with more timing advance than is specified... around and up to 6 degrees more. The wider end shortens the gap from rotor to inside the dissy cap points.
Heck, why stop there? Order a new distributor cap and may as well change the leads too.... :eek::eek::eek:

[pop058]

Engine number prefix should clue you on the capacity and compression ratio of your motor

[ecodan]

Thanks guys.
Forgot to mention cap rotor button and leads are new, and i just fitted a vacume advance and visusly checked it was working.

Reason for questioning the engine capacity is that being clearly labled a 3.5 on the engine, i have no way of knowing if they lengthened the stroke to 3.9 during the rebuild hence the crappy after market ecu. However I realise i could be barking up the wrong tree.

Further info... Idle is Very smooth, timing is at 6btdc at the mo. But i doubt that would account for the complete lack of acceleration at highway speeds. Especially given it pins you to your seat taking off from the lights.

[bee utey]

A 3.5 is the same stroke as a 3.9. You can't easily "recondition" one into the other as the blocks are a different bore size. Read the first few digits of your engine number (next to the dip stick tube) and plug it into a LR engine number data base. The external accessories from a 3.5 will bolt on to any of the bigger capacity blocks so are no guide to capacity.

Rover V8 Engine Numbers (http://www.rimmerbros.co.uk/content--name-Rover-V8-Engine-Numbers)

Check that your distributor has fully working mechanical advance. base timing can be raised to 10 degrees on low compression engines no probs.

Mixture wise you need an O2 sensor in the exhaust to get any idea of what is happening under load, there's all sorts of stuff out there if you're interested. Even a cheap narrow band sensor will tell you something with little more than a simple multi meter. 0V lean, 0.8V+ rich, look for transitions as you power up.

You can lever off the cover of the flapper and adjust the spring preload to change the mixture profile. Make sure you keep note of where you started from so you can go back there.

[ecodan]

Thank you.
Will find out the engine number and take it from there.
I have a spare flapper, so can play with that one and not risk the other.

[loanrangie]

If its a 3.5 block its possibly been stroked which would explain the aftermarket ECU, so it could be 4.2 + capacity.

[ecodan]

Is their any way to find out without dismantling part of the engine?

[DoubleChevron]

couldn't you verify the stoke and piston size by dropping the sump :confused:

seeya,
Shane L.

[loanrangie]

couldn't you verify the stoke and piston size by dropping the sump :confused:

seeya,
Shane L.

Yes the crank should tell you if its been stroked or not, pistons not really unless you removed one to measure the gungeon pin height.

[PLR]

Is their any way to find out without dismantling part of the engine?

G`day ,

as it doesn`t need to be exact .


If you put a rod down a plug hole and rotate the engine through a full rotation , you should get an idea .

71mm is a std 3.5 a stroker will have around 86mm

The stroker will be second oversize , 20 thou but you can`t find that without dismantling .

The Australian flapper ECU lack what the UK ECU has , an enrichment at full throttle but i doubt cause for your situation .

[ecodan]

So this is where the engine number sits... Factory 3.5L

23D00001

R.Rover/efi auto 8.13:1cr

1986 onwards


Does this mean we should be looking at timing around 10btdc?

Also, thanks for all the other guidance guys, I'll have a look at flapper spring tension and piston height through the plug hole when my Son and I are in the same place with the car again!

[PLR]

So this is where the engine number sits... Factory 3.5L

23D00001

R.Rover/efi auto 8.13:1cr

1986 onwards


Does this mean we should be looking at timing around 10btdc?

Also, thanks for all the other guidance guys, I'll have a look at flapper spring tension and piston height through the plug hole when my Son and I are in the same place with the car again!



G`day ,

this is only a suggestion , there`s no reason not to do as you`ll be advised .

Google how to set ignition timing with a vacuum gauge .

This takes into account the wear in all parts .

The numbers at the crank only mean something if the TTDC mark has been found and recorded , otherwise they are a guide .

[Homestar]

I'd be running at least 10 degrees if not 12. One of my 3.5's had 15 degrees dialled into it by the PO and it still went fine unless it was a hot day under heavy load. :)

[ecodan]

Okay set to 11degrees, definitely improved performance, so will adjust flapper next to increase fuel as still feels like it's starving under heavy acceleration.

Also will do stick stroke test through spark plug hole.

Probably unrelated, but a re-occurring problem is occasionally the car will crank till the battery is flat without catching. Majority of time it starts first crank, even when very cold.

[superquag]

Okay set to 11degrees, definitely improved performance, so will adjust flapper next to increase fuel as still feels like it's starving under heavy acceleration.

Also will do stick stroke test through spark plug hole.

Probably unrelated, but a re-occurring problem is occasionally the car will crank till the battery is flat without catching. Majority of time it starts first crank, even when very cold.

Next time it plays this game, check to see if you (a) have spark, and (b) there's enough bite in the spark. You mentioned 'new' distributor cap/rotor/leads... but I'm guessing you have'nt replaced the LUCAS ignition 'amplifier'

In the mean time, you could implement 'Gap Theory'. As an Industrial Sparky colleague of mine was wont to declare..

"Most electrical problems are caused by GAPS. Either a gap in the wires where there's Not supposed to be a GAP, or the lack of a GAP where there should be a GAP"

- Check every possible plug/connector in the Fuel Injection and IGN circuits, especially any 'Earths' to the body... - Land Rover has a well-earned reputation for designing & assembling dodgy "Earth Returns"

EDIT:- Vacuum gauges are not that pricey, and going on the Google articles, could be a worthwhile approach. http://www.ebay.com.au/itm/Mini-Dial-Air-Vacuum-Pressure-Gauge-Meter-Vacuum-Manometer-30inHg-1bar-8H9R-/291588705923?hash=item43e40a8e83:g:7G0AAOSw37tV8-Z-

[ecodan]

Sage advice. Unfortunately untill the fault persists, i'm having trouble recreating it long enough to check the spark.
The Module sounds interesting... Shall investigate, though its not missing under load.

Meanwhile I'm going to change the fuel pump relay.

On other news, adjusting the flapper spring 5 notches anti-clockwise definitely gave more power through the flat spot. As did cleaning the contacts and strip.

[ecodan]

Noticed since I altered the spring on the flapper, cold start idle is now a lot lumpier yet fine when the car warms up. It's not bad, bad, just not as smooth as before. Any thoughts?