Rover v8 mx5 won't rev up

[Rover v8 Mx5]

Hi there,

Just joined this forum so be gentle.

I've got a 3.5 rover v8 in a mazda mx5 with a supercharger on the top pushing 12psi.

It's running the tvr tune resistor as it's more rich, exhaust was glowing red before this was changed, very lean

It runs lovely up to about 3k rpm then it backfires, lots of black exhaust, almost like a popcorn limiter.

So far I've replaced/checked

MAF - changed as was reading 50 percent at idle on direct in rovergauge. New one reads same 50 percent, maybe vaccum leak? Also noticed brakes are very hard, there there but very weak, maybe vaccum related.

Ignition coil, replaced - genuine, no luck

Plugs

Plenty of fuel pressure

I'm thinking either timing or ht leads?

Any help is much appreciated.

Rowan

[scudderfish]

We're lovely here I'm sure people more knowledgeable than me will be along, but you have to post some photos, your car sounds awesome!

[Ian Anderson]

Start it in the dark and then give it a rev and see if there are sparks between the spark plug cables.

Rover manages to do this quite easily and will cause backfiring etc.

Ian

[stevieturbo]

Hi there,

Just joined this forum so be gentle.

I've got a 3.5 rover v8 in a mazda mx5 with a supercharger on the top pushing 12psi.

It's running the tvr tune resistor as it's more rich, exhaust was glowing red before this was changed, very lean

It runs lovely up to about 3k rpm then it backfires, lots of black exhaust, almost like a popcorn limiter.

So far I've replaced/checked

MAF - changed as was reading 50 percent at idle on direct in rovergauge. New one reads same 50 percent, maybe vaccum leak? Also noticed brakes are very hard, there there but very weak, maybe vaccum related.

Ignition coil, replaced - genuine, no luck

Plugs

Plenty of fuel pressure

I'm thinking either timing or ht leads?

Any help is much appreciated.

Rowan

Quite a few red flags.

Firstly no engine vac/brakes.....and the supercharger. Something is massively wrong there. What is the idle speed ? What timing does it have at idle ?
Get a proper measure of mixtures at idle too ( wideband would be sensible here )

But no vac sounds like something is plumbed wrong.

Glowing manifolds will nearly always be far too little, ie. retarded timing.

Don't throw parts at random, test.

Of course, are you just winging it with the install and whatever this "resistor" mod is ? Or is this some actual tried and tested, well proven thing to do ? And if there is a MAF involved, where is it installed ?
And also what type of blower ?

[Rover v8 Mx5]

Hi guys,

Thanks for the warm welcome and swift responses.

I started the car up last night and there is no sign of sparks between ht leads (only some angry neighbours )

Pleaee see spec below.

Eaton m112 charger
4.4 fuel pump
Intermediate front timing cover
Uprated oil pump
14 cux ecu.
Fuel injected.
No lambda sensors ( the loom is there but I know it has ran in its current configuration correctly, but will be looking to install these.
Straight through exhaust

The 14cux ecu can select different tunes based on a "tune resistor". These alter fueling parameters only I believe.

Not sure of idle timing, how would I check this?
I'll grab a video of the issue I'm having this afternoon.

The MAF is installed before the supercharger, with a k and n cone filter attached to the intake side of the maf.

Idle is currently at around 1100rpm when cold, then once up to temp idle is around 850-900 rpm

Please see attached pics of install

Rowan

[Rover v8 Mx5]

I may sound daft here, but it's just crossed my mind that it looks like the red vaccum hoses are attached to the output side of the charger vacc advance also

[Rover v8 Mx5]

I'll post a rover gauge log also

[stevieturbo]

You need to know mixtures, no guessing or assumptions.

Timing....with a timing light of course.

[Rover v8 Mx5]

Hi stevie,

First of all, I'm obsessed with your capri!

How do I see mixtures?
I'll get a timing strobe ordered.

Please see attached





Many thanks
Rowan

[stevieturbo]

Hi stevie,

First of all, I'm obsessed with your capri!

How do I see mixtures?
I'll get a timing strobe ordered.

Please see attached





Many thanks
Rowan

I don't own a Capri ?

As already said, you can check mixtures with a wideband lambda.

[stevieturbo]

And that is clearly off cylinders, it is not running on all 8 in that video.

[ChrisJC]

And that is clearly off cylinders, it is not running on all 8 in that video.

That was my thought - there is something wrong with that engine!! I would run a compression test on all the cylinders to make sure there's no serious engine damage going on.

It might however be just swapped plug leads - double check they go 1-8-4-3-6-5-7-2 around the distributor.

Chris.

[Rover v8 Mx5]

Thanks guys,

Your scaring me! Hopefully nothing too serious

Checked the dizzy cap and all plugs are going to where they should be.

I remember the guys who sold it to me mentioned about the dizzy cap being rotated, they have written the cyl numbers on the cap, not sure if true, the garage was not pleasant, seemed very dodgy so questionable

Please see attached. Hopefully if there's anything wrong with the cap someone with a trained eye can spot it.

Checked inside cap and the points have slight degradation but nothing too bad, there not making contact, that's for sure.

I can see alot of corrosion on the ignition amplifier, but I believe the engine would not run atall if that was faulty?

I think I'm going to get a compression tester before I spend more time or money on this, is there a particular type required or just a generic amazon special?

Thanks
Rowan

[Rover v8 Mx5]

To clarify,

1-8-4-3-6-5-7-2 round the dizzy, clockwise

Time for a comp test I think to see if I'm wasting my time with this engine

Would it be possible to adjust the timing. Retard 10 degrees or advance 10 deg? I've read that to set it correctly you advance until it pings then take it back slightly.

What sort of wideband lambda may I need, and can anyone recommend a decent timing strobe that won't set me back too much?

Thanks guys this one really has be stumped, I've worked on engines a lot in my spare time, starting to pull hair out with this beast!

Many thanks
Rowan

[stevieturbo]

To clarify,

1-8-4-3-6-5-7-2 round the dizzy, clockwise

Time for a comp test I think to see if I'm wasting my time with this engine

Would it be possible to adjust the timing. Retard 10 degrees or advance 10 deg? I've read that to set it correctly you advance until it pings then take it back slightly.

What sort of wideband lambda may I need, and can anyone recommend a decent timing strobe that won't set me back too much?

Thanks guys this one really has be stumped, I've worked on engines a lot in my spare time, starting to pull hair out with this beast!

Many thanks
Rowan

So you know nothing about this engine ? has it ever ran good with or without the blower ?

And is it really an old dizzy with points ? Are they set correctly with correct dwell etc ? ( essentially this is what you're actually trying to achieve when you set the points gap )

On that basis, an old timing light with a built in dwell meter would make a lot of sense....but probably a rarity these days, if one even exists for sale.
Dialback or advance feature is good to have, and of course an rpm display.

Wideband, there are a plethora of options. Cheapest searches come up with

https://www.ebay.co.uk/itm/204149405931

https://www.ebay.co.uk/itm/185270685548

Never heard of the first company, but PLX have bee around a very long time and make decent stuff.

Prices on a lot of others seem to have gone up quite a bit.

And if you advance until it "pings"....good chance you'll blow it up, even more so if you're trying to listen with your ears just sitting in the car.

But that's a bit further down the line to worry about vs just getting it idling, revving and driving half right.