mark kibort

So i mentioned before that this car is running a little strange. starts hard warm, once it catches, it takes 30 seconds of runnig and wildly hunting RPM to stablizie. idle stablization valve?? its fine after that?? fine cold .

so i checked the fuel pressure, and i measured 18psi and reving the engine, it goes to 21psi. i dont think anyone has ever mesured fuel pressure, just pulled pressure out and put pressure in to keep the car from pinging. i havent heard or felt a ping only if its lugging in 1st letting the clutch out too early and with too much load.

since it has 30lbs in jectors, but only has 320rwhp and 375rwt, i imagine if im running 30lbs injectors and have 44psi presssure i would think that the low pressure could be a problem for the hot start, and could be a problem for its lack of power and pinging occasionally.

thoughts??

John Speake

At those fuel pressures the injectors won't be atomising the fuel properly. Get someone with a Sharktuner to make you a stock EPROM for the LH except with fuel injector size set to 30#. If they don't have an EPROM programmer, get them to send you the binary file set to the 32kbBi option tand then get someone to blow a 27C256 EPROM using the file provided. Then turn the fuelpressure up to 55psi.

The better long term solution would be to buy a PEM for the LH, get someone with a ST to set it for 30# injectors, and send it to you. Then you have the car ready to go to do a proper LH tune.

BC

If you destroy this engine with your purposeful ignorance and refusal to get a sharktune I hope no one here ever "supports" your racing again with anything other than a "good luck, chuck"

John Speake

I think this is a 6 litre road car Mark has borrowed, with a Devek engine... but yes, it clearly requires a good tune up.

jcorenman

The fuel pressure that is "felt" by an injector is the difference between rail pressure and intake pressure (vacuum). That's why there is a vacuum line on the fuel-pressure regulator (and dampers). The stock LH tune is based on an injector pressure of 55 psi.

Fuel pressure measured with a gauge is called "gauge pressure", i.e. relative to atmosphere. To make it meaningful, measure with the engine off (and manifold at atmospheric), and fuel-pump jumpered. Always. Numbers quoted with engine running are meaningless.

For example, if your intake vacuum is 7psi, then your 18psi gauge pressure is really 25psi injector pressure-- but I am guessing.

In any event, that is stupid-low. As John says, injectors don't work well at low pressure, and you are very far from the factory tune... basically wandering around in the woods at midnight with no flashlight.

How can you adjust fuel pressure without a gauge? (I know, with a wrench...).
If you are hearing pings then you are damaging the engine. And why would pulling pressure out help with pinging??

Yep. Although the pinging is more likely higher-than-stock compression, with stock ignition maps.

A couple... There is a tool which can be connected to your engine and will tell you whether your fueling is rich or lean, and by how much, and let you log that data while you drive. It will allow you set the injector size properly, and let you change the maps for any RPM and load, and properly compensate for engine temperature for warmup. It will also report on the EZK's knock-retard, how much and which cylinders, and allow you to set the ignition advance for any load and RPM. Knowing when and where the EZK is retarding timing is extremely valuable information, and staying within the EZK's retard range is critical. You can log all that data, for hours at a time if you want, and take it home and tweak your ignition and fuel maps with a few keystrokes. In addition, having access to the ignition maps also means you can set up one map for race gas with more aggressive timing, and another for street gas-- just wire a switch to the coding plug.

Considering all that you have invested in the engine and your car, in terms of money, sweat and passion, how can you not have one of these tools? It is called a Sharktuner, designed by a couple of very clever guys in the UK, and available for a pittance, considering all that it does.

[Edit: I understand that this isn't your car, but my point stands: You need a Sharktuner for your own car, and an extra pair of PEM's for this car].

IcemanG17

MK
Gotta do the sharktuner..... the 6.0 car CLEARLY needs it and I am SURE you could find lots of extra HP in your race car too....

There are a couple locally in the Bay Area.... One owner even has a DYNO too...

Rob Edwards

I bought a pair of PEMs and sent them, a WBO2 and my ST2 to Kibort (by way of Bill Ball) in May 2011 in hopes that he'd use them on the racer (I have $100 in that engine too). Bill kindly offered to help with the Sharktuning.

https://rennlist.com/forums/8551180-post242.html

Got 'em back in December, not sure that they ever made it into the car. You can lead a man to water, but you cannot make him drink.

Mark Anderson

Some men even more so

brutus

Even more of a problem if the man thinks he can walk on water.

BC

I did not connect that this was yet another car he is trying to bludgeon.

andy-gts

MK,

Just find a local tuner , that is familiar with sharktuning and get a dyno and for 100 bucks an hour you can have your car perfectly tuned.....just do It!!!!

Or ship your car to kcmodified and they will do it for 750 bucks... it is quite a deal as I struggled with no dyno sharktuning for weeks.... this is done in one day and awesome.

123

Who needs water when you've got Amsoil?

danglerb

Leading them to water may not do the trick, but holding their head under works really well, except they may be cranky after their drink.

mark kibort

thats what im thinking as well. why would all these builders put in 30lb injectors vs stock when the expected HP gain is only 30-50hp?? just turn up the fuel regulator like i did and you are set. my cars have aways run great and safe for racing. i think the best design for my 6.5 liter at 375rwhp would have been the 85 injectors i was running 70psi with the S4 with gt cams and now, i cant get the 6.5 liter lean enough with the 30lbers.

dcrasta

Wow? ? ? Really ?

We are talking modern MPI systems? I have never seen a EFI MPI setup with less than 30PSI on the rail. 36~40 psi is what I'm used to seeing even on NA cars. Turbo cars usually have a boost referenced fuel pressure regulator, and its typically a 1:1 ratio. Why your fuel pressure is so low at Idle is amazing and not very typical. What will end up happening with that low pressure is your injector pulse will have to be very long, and that will cause problems at high rpms' . Using injectors sized for a 5.0 motor (And sized pretty small I may add) will cause problems on a 6.5 liter motor (pretty easy to see why.) Preferably you would want to have large enough injectors so you can run a sane Fuel line pressure and still have the headroom so that you are not maxing out your injectors at the top of your operating envelope.

I have tuned turbo car's for years and if you are running that much pressure on the rail its usually a sign the injectors are undersized..

Wow.. <SMH>

From all the information you posted sounds like you need someone with a WB 02 sensor, knowledge of Sharktuner, a good dyno and a few hours (Days) of tuning or you will be rebuilding something soon.. Many internet calculators for injector sizing and other things that are useful when putting together your baseline tune.

[skill and experience matters here, no time for beginners..]