SP ENGINE MISS AT 4-4,500 RPM

[fredbareoz]

Hi there
Okay, been having issues with this since we have got the car.
esp noticable in second and third gears, you try to balance the car on the throttle or back off and the thing has a big miss. sometimes pig roots badly. Blows heaps of black smoke and it feels like its leaning off. My guess is its actually getting too much fuel. Boost is also down. Although with some fiddling we have got it up from 4 pound to around 6-7. Not where it should be though.
Have swapped over the air flow meter. have tested the O2 sensor on the MMDS and swapped over from a donor vehicle (just in case)
Rang Chip torque, they suggested we have a leak somewhere. It all appears to be good on inspection. The intercooler looks sound (no cracks)
Even with my contacts i am having trouble finding some one who can tell me how they govern the fuel.
We dont think its in the blow off valve but am willing to try anything to get this SOB to run properly

H E L P !!!!!!!!

Thanks

Al

[Hammer]

My advise is to contact MX5 Mania (click above ad link of this forum).

They work on a lot of SPs. Daniel who worked with Allan Horsley when they developed the SP, also works there from time to time. Both David and Daniel should be able to provide some guidance on what's causing it.

As it happens, I just picked up my SP from them today after a major engine rebuilt. It was rebuilt with better pistons and conrods - no modifications. The original Mazda Conrods where starting to bend - I'm lucky none broke. Otherwise, it could have broken through the engine block.

Now my car feels just AWESOME!!!!

[stevesports]

ah, he's in melb. I guess you could call them? Have you tested for vacuum leaks using soapy water?

otherwise give dick or tony a ring.

[Hammer]

ah, he's in melb...

Yes I know. That's why I said "contact them". He's after some advise, and I'm sure MX5 Mania will be more than happy to provide some advise over the phone.

PS. I'm not affiliated with them whatsover, I'm just a happy customer.

[Juffa]

Al,

You mention that you think she is running rich at times. Have you checked the AFR to confirm this? Do you have access to a exhaust gas analyser in the workshop? If not, a workshop with a dyno should be able to check the AFR at various points.

just my 2c worth.

J.

[mx52nv]

As an ex-SP owner, I can attest to this problem existing and can also add that you are hitting the boost cut, which in the case of the SP, also meant a fuel cut. This was particularly dangerous for me as I was actively competing and the problem always occurred when I entered the first corner of the sprint track. This made it very difficult to hold the correct line and hit the apex

Running on the dyno may pick this up BUT the problem only occurs usually in the higher rev range in 3rd gear AND while feathering the throttle.

All in all, unless you are happy to start playing with the factory ECU or replacing it with a new aftermarket programmable one, no cheap solution there. However, if any other SP owner has had similar problems and found a cheap way around it (that has actually worked), please do share

As for amount of boost, I was under the impression that 6-7 psi was the standard setting. Although this varies a little between each SP, I don't think that boost was set any higher.

As for the boost being at 4psi, this was exactly the same problem with Bob's old SP - the car was a real 'bad apple' compared to all the other SPs within the WA MX5 Club. After numerous checks, dynos, sending the ECU to Chiptorque, replacing the actuator with a new Garrett replacement, the problem was finally solved when we installed a Electronic Boost Controller that was set at 7psi. Although this made sure that the minimum boost was 7psi, boost still still crept up to 9psi momentarily in the upper rev range. Bob really did not mind too much in this case as from an underpowered SP, he went to the most powerful SP in the club

Granted the unstable boost was never really solved for whatever reason, at least minimum boost was maintained.

As a side note, all SPs run rich from the factory - the general consensus is that this was to ensure that the SP would last through the 3 year factory warranty. Most SPs will have a large amount of unburnt fuel/soot that is left behind the exhaust tip and ground.

I hope this provides an insight and some possible solutions to your problem.

[Hammer]

Thank goodness, I extended my warranty to 4yrs. As on that 4th year, my turbo was replaced under warranty.

I later found out (when warranty ran-out), Mazda replaced the turbo with a wastegate that was only rated @ 5 pounds. This was confirmed by Daniel @ MX5 Mania through the serial number on the new wastegate.

Prior to the replacement of the turbo (the original one), I participated in one of the dyno days, and my SP was producing just above 7 pounds of boost.

As a result, during my recent rebuilt, Mania fitted a boost controller and allowed me to increase the boost back to the standard 7-8 pounds range.

But as MX52MV already mentioned, what you're experiencing is the way the SP was tuned - albeit yours might be more on the excessive side. I experience jerkiness (or lumpiness of torque) around 5000 rpm, while the throttle is being feathered. I notice this most in 2nd gear. Though on occassion, I will get it in 3rd. Rarely on 1st, and never on the other gears.

I was told the only way to overcome this is to fit an aftermarket computer that is piggybacked into the factory one, then it can be tuned properly.

Benny had his done and when I was taken for a drive in it, I gotta admit, apart from noticing a bit more accelaration (ok, way more) , it was smooth, linear and tracktable. It felt like a V8 with the way it produced torque.

I was quoted around $2500 (can't remember exact price, but its around there). This include a piggyback computer, bigger injectors, a new air/fuel sensor & electronic boost controller. This also included labour and tuning. I'm seriously considering it. But at the same time I don't really want to modify my SP. They're worth more un-touched.

[Alex]

Quick question, is your car stock of have you done mods.
I thought the SP's only hit the boost cut after intake or exhaust mods?

[mx52nv]

I thought the SP's only hit the boost cut after intake or exhaust mods?

Hi Alex,
Hope I'm not hijacking your question to Al (the OP) but all three SPs that I worked on in the past were almost bog stock except for a K&N drop in Panel Filter Element in the Carbon Airbox. Technically, I suppose this counts as a "intake mod".

They all had the stock exhausts and all three presented with the problem.

As both Hammer and I have mentioned, the real solution is to get a proper programmable engine management system to sort out the tune. My only experience with NBs have been using Autronics and WOLF V500 ECUs so I can vouch for them in this instance. However, it will cost $3k-$4k approximately installed and dynotuned. Use a plug extension and you could make it plug in so you can remove it in the future if you wish to sell the SP.

If you do go down this route then I've said it before and I'll said it again - choose your tuner before you choose your ECU.

Just as a final thought, none of the SPs that I've mentioned actually went to an aftermarket ECU as they all felt a stock SP was worth more in the long run.

I, however, would have done it if owning both the SP and my old NA turbo was financially viable
In the end, I had too much heart and soul in my NA and sold the SP

[bigdog]

Mine has always done this - more so with the T piece mod than before. My solution has always been to drive around it by driving more like a race car - full throttle or brakes when pressing on, or very light throttle and short shifting in traffic and around town.About the only time it really annoys me is running hard uphill - I often find it cuts mid corner and upsets the handling. I don't understand why the ecu change is so expensive - based on IT developments they should be much less - what they do is not complex, and the components are not expensive.I guess we're paying that elusive 'copyright' figure for someone's development, but they should still get cheaper over time, yet they seem to get dearer! Apart from cost I hesitate to modify my car from a legal perspective. I don't want the agro of defect notices etc - that's why I bought an SP and not a red turboed NA6 . With the moves to crack down even further on this area I will just continue to drive around it for the time being anway.

[Garry]

Hi Al,

Have you tried replacing your BOV (recirculating valve) with a know good one to find your missing boost? The plastic Bosch ones aren't particularly durable. I've been through 2 Mazda ones already. Currently I'm using a Bosch one from an old model Porsche. It looks the same as the original but it seems to be more durable and it's characteristics seem to suit the SP better than the one Mazda chose. I tried an aftermarket GFB one and it's characteristics didn't suit the SP at all.

By miss I assume you are talking about the stumble when backing off the throttle a little? As others have said the only way to get rid of it is to change ECU's to get rid of the MAF. As it was explained to me a long time ago it's caused by air flowing through the MAF in the reverse direction after the BOV opens. Unfortunately the MAF works just as well in the reverse direction. So if you've got a full head of boost, back off the throttle, even slightly, the BOV opens and big wack of air heads towards the turbo intake pipe where some air then goes back into the turbo but some also heads back towards the MAF. The MAF thinks the engine has just taken a big gulp of air so tells the ECU to dump in a whole lot of fuel and the engine momentarily drowns until the BOV shuts again and the air starts flowing the way it's supposed to.

I've found that different BOV's make things better or worse as I alluded to up the top. The GFB valve was very twitchy and opened very quickly which made the stumble much worse. The guys at GFB wanted me to take it back so they could play around with spring rates etc to get it to work better on the SP but I never got around to taking it them. The valve from the Porsche opens slower or the flow rate through the valve is less than the GFB valve and the stumble is not as intrusive. Though it's still there and under high boost, high load conditions the stumble can be quite severe.

So it's an SP "feature" you'll have to learn to live with and change your driving style to reduce it, or shell out some $$$$ for a new ECU and all the other problems that creates.


Hammer,

The replacement turbo I got from Mazda under warranty was also set around 5PSI. I'm guessing Mazda changed the specs to help stop the rods from bending. The subsequent replacement aftermarket turbo I bought was also set to around 5PSI.

[Rotary]

Has anyone tried plumbing the Blow off before the MAF, as in between Air filter and MAF or in the filter box itself?
If the problem is as gary described, then this should reduce the disturbance to the MAF readings

[Garry]

There isn't much room between the airbox and the MAF and I'm not real keen to hack up my $3K airbox to try it out. I was toying with the idea of getting another nipple fitted to the turbo intlet pipe closer to the turbo and further away from the MAF to see if that helped but never got around to seeing if it could be done.

The SE plumping seems very familiar to the SP but they dont seem to have the same problem. Maybe with the addition of the boost sensor to the SE Mazda was able to do some trickery in the ECU tuning to avoid the over fueling?

[Rotary]

without knowing the problem entirely(probably need to see it) its hard to speculate on exact reason and solution.
but if indeed a MAF issue, then the only way would be to have it plumbed before the MAF, or into a seperate muffled box of some sort.
But it should most likely sort it.

One way you could try it, is block of the return in and the leave the Blow of side in free Air and see if there is a difference

[Benny]

I doubt there is anything you can do to stop the stumbling problem, which only surfaces if you back off the throttle while the engine is under boost, unless you get ridof the MAF sensor and go to an aftermarket computer.
This "pig-rooting" is terrible and makes the car hard ot control sometimes as it's impossible to feather the throttle when going around fast bends.
Like Dave, I leartned to drive around it, but sometimes you have to feather the throttle rather than keep the boot in all the time.

I have the Mania add-on computer and my car is as smooth as silk.
Even smoother than an NA stock car.

When selling the car, I intend to revert the car back to stock, which is quite easy.

Daniel at Mania can tune the add-on computer so well that I wouldn't hessitate in highly recommending him.

By the way, the rods bend very easily, and there is probaly not one standard SP that doesn't have at least one bent rod.
When I had my engine re-built, I had 2 bent rods, and I would recommend you put in forged rods and pistons, then you can go to town with boost and power levels.
My car is just amazing now.
It has heaps of power all over the rev range, and is so easy to drive.
There is no lag at all and it feels like there's a big V8 under the bonnet.
You can back off at any time, and it just decelerates exactly as you would want it to and when you put your foot down, it just explodes!

Even if I take off gently then put the boot into it, it starts wheelspinning at around 4000 RPM, then change to second, and if the road has any moisture on it, it will start wheelspinning again when it hits 4K, but the throttle is so adjustable that even just a tiny flex of your ankle will give you the desired affect.