Jfrahm

Hi all,
In another thread I am working on getting my 1987 928S4 with a Murf Stage II to cold start. I bought the car from my brother's estate hoping to save it from a part-out or god knows what. Long story. Anyway...

I am looking at the injectors and I see they are Ford 30lb/hr at 3 bar.

Stock 0280150730 are 18 lb/hr at 3 bar.

So these are flowing 65% more fuel (?) I do not see any indication in the manual I have (emailed by Tim) that there are chips included in the kit. Does this mean it just runs pig rich until it gets into closed loop?

I know the Stage 2 is superseded but it seemed to run OK before I dug into it to deal with some issues, check the timing belt, etc.

Thanks,
-Joel.

Imo000

You are missing either a chip set or a fuel management unit/rising rate fuel pressure regulator.

Jfrahm

So you think that the Murf Stage 2 is supposed to have chips? I have the FMU but it is plumbed after the stock regulator and thus would not pull the fuel pressure down to correct for a rich open-loop condition with oversize injectors.

There is nothing about chips in the instructions. I have not looked at the LH but I believe this one had been opened in the past to put aftermarket performance chips in so I'd have to actually examine the PROMs.

hacker-pschorr

Post edited - incorrect information posted. See Tim Murphy's post below.

FredR

You need to check what eeprom programming the LH is currently running. It would seem somewhat stupid to simply stick bigger injectors in without modulating the fuel flow to each injector. Earlier attempts at programming typically used the original sharktuner to burn a different program to a single shot new burn eeprom and I dare say someone who went to the trouble of doing these mods would probably have known this. what you now need is to fit a set of PeMS nito the LH and Ez units and have access to the latest version of Sharktuner

Sticking 30lb injectors in will change the AFR from around 13 to something in the region of 8- utterly pointless and probably would not run like this, at least not for long.

Regards

Fred

Tim Murphy

It's been a long time since Stage 2 kits were produced, so I have to think a bit what was all done.

They did include 30lb injectors and a Vortech Super FMU, and I think a fuel pressure gauge kit. This FMU allowed you to set fuel pressure and had an 8:1 disc in it that would increase fuel pressure under boost. At 10 psi it would wick it up close to 100 psi and make the mixture pretty rich. This and the knock sensors helped keep ignition reasonably safe. I did test this after I bought one of the very first Shark Tuners and although there was knock present in the upper RPM it would never exceed what the ezk was able to adjust for it. With each knock present the ezk would pull out 3° timing advance up to 9° max. It would never get there. I believe we set the fuel pressure to 42 psi with the vacuum line disconnected which allowed it to run stoichiometric while at idle and cruise, with help of the adaptation of the LH. This is very close to what Vortech did on the supercharger kits for 5.0 Mustangs at that time.
This is way before the Shark Tuner was available and is really old school by today’s standards.

Today, Stage 3 kits get a machined aluminum elbow for the intake with an air straightener glued into it. The MAF gets a special re-calibration disc mounted in it, 42lb Bosch gen 3 injectors slightly modified to fit the 928 fuel rail, and custom Murf 928 chips for fuel and ignition. The rest of the fuel system stays stock. Instead of 8-10 psi the Stage 3 now runs 13-15 psi boost which ends up to be about 60-80 more rear wheel horse power.

Hopefully that answers some questions.

hacker-pschorr

Totally forgot about the Super FMU's. It has been a while......

Jfrahm

Thanks for the info. I have ordered some injectors to take it back to stock fueling, actually they are Gen III Ford injectors. Hopefully with these I can get it running with the supercharger disconnected and that will be a step forward. If the Ford injectors seem like a new set of problems I can pirate the injectors from my other car but I would prefer not to do that.

I do not have any of the stock parts to convert the car back to stock, so it'd be a challenge to try to sell the supercharger kit separately. My goal is to get to a point where I have a car I can sell for decent money, balancing the time and money I put into it with the selling price. The car is sort of an albatross for me, I regret getting involved but with 20/20 hindsight. Ah well.

karl ruiter

I'd buy a complete stock intake from Mark or somebody. Pull the Murf system and sell it separately to someone who wants to tinker.

Jfrahm

Actually there are a lot more parts than just the airbox and intake tubes so it'd be a bit of a big job, and then I'd have multiple pieces to market as well as the car.

I expect to get the injectors in the next few days, if I can get the car to run well w/o boost on stock fueling I will consider my options. The car might be struggling more at altitude (Boulder CO) with the 30 lb/hr injectors than it did at sea level and that is the root of my problem. I want to validate that assumption and get the car running well w/o boost and then evaluate, that is usually what I do with modded cars.

I think it might be possible to drop the base fuel pressure with the 30 lb/hr injectors and get to a decent tune, and a new owner could take on sharktuning it if that was their desire.

Jfrahm

Hmmm well the stock size injectors are fitted and no improvement in cold start. Better idle after I do get it running though. Puzzling. I am going to follow up in my other thread as at this point I do not think the supercharger is relevant.

Jfrahm

As I updated my no-start thread. I swapped in another ECU and it starts right up. So that's good, although costly.

I am not sure what I am going to do next, re-fit the 30 lb injectors and/or mess with the tune. I will think on it some. I should hunt up some 17mm lower injector O rings in any case, I do not want to re-use the ones I have again.

Thanks for the info!
-Joel.