mark kibort

Are you talking my car or the 6 liter... this isnt my car that has the issue.. this is the street 6.0 liter from devek.

now, what kind of computer **** would you recommend for my car, and what is the expected gain?

who is "everyone else" ? my competitors (mustangs) with engines that are much more advanced and have the ability to make 450rwhp, just with ecu tweeks and all out of a 5liter..... they are grossly different. (eg '08 mustangs)
so far, not many people have put down as much hp as i have with a stock 5 liter engine. can you name them???? oh yeah, half of them have blown up

sometimes the carburetor approach works for ball parking functionality. having a 11:1 to 12:1 fuel curve from beginning to end , is not a bad thing or too far off optimal.

again, Bill hooked up all the diagnostic testing equip and we went out to peg the rev limiter. it seemed to him that the car was very healthy .

Rob Edwards

You have a car that won't even start. The 'gain' is being able to figure out why, in some semi-rational matter.

GregBBRD

I think that someone with Kibort's incredible knowledge about the fuel system on the 928 model could solve a simple starting problem, without starting a thread about it.....

mark kibort

I have a perfectly running car. Greg, you are taking on a Troll form.

mark kibort

My car starts and has always started fine.. (for the most part) there has been plenty of help here in diagnosing the times over 30 years that it didn't. green wire, ajar EZK box connection, ground wire cut by suspension, etc.

so, why do you think my approach to this is "irrational"? there are plenty of things that can be wrong. im looking at the most likely first.

that fuel regulator (because it seems there is no fuel pressure)
the fuel damper, but its clear, that leak would have to be POURING into the vacuum lines
or the fuel pump.... can be tested at the entrance of the fuel damper by seeing if at that point, its producing a pressure stream .

by the way, I haven't seen the car. this is all over the phone.... so I think im helping a 928er in a very logical way.

you, on the other hand, seem to insinuate that you need a shark tune and replace everything to diagnose and fix the issue. news flash, some good old "logic" can usually fix these things. The only gain I can possibly have on my car, is more power and I haven't seen to much of that for just a 1 point change and optimization of a fuel ratio. However, if there is a proven 30hp gain, I would make the computer change tomorrow. (and if it was proven safe)

jcorenman

Mark: Pay attention to what Stan, Duc and others have said: If you (whoever is working on the car) smell fuel in the vacuum lines then find the leaking damper or regulator and replace it. It is not about pressure, it is all about dumping fuel into the manifold via a damper/regulator with a busted diaphragm that lets fuel (under pressure) into the vacuum lines.

PEMs and Sharktuners and computers is science, we don't need no stinking science...

jcorenman

It's actually sqrt(30/19) too much fuel but it's a 6.0L which needs (6.0/5.0) more fuel, and ironically the worn-out MAF probably helps (reads low = less fuel). Opening-time is the wild card which makes it all work.

(MAF ohms only matters for 85/86, not used for the LH 2.3).

Rob Edwards

We're not talking about your racer, Mark. Apologies if it wasn't clear that I was talking about the non-starting 6.0 liter street car that doesn't belong to you, and not your track car, I thought that would have been self-evident.

I didn't mean to imply that your approach was irrational, I'd honestly like to see the owner of this '88 6.0 car get his car running right, and it certainly sounds like there are problems with fuel delivery. Perfectly reasonable to replace dampers with split diaphragms as a 1st step.

Jim, didn't realize MAF ohms were not relevant to the operation of LH 2.3- is the resistance across pins 4-6 still a good assessment of MAF health for 87-95 cars, or no?

Randy V

Well, that's the first hurdle.

jcorenman

The resistance between pins 4-6 on the MAF is the potentiometer which is used to adjust fueling for the LH2.2 (85-86)-- not used for 87+.

The resistance check for the hot-wire sensor is between pins 3 and 5 on the MAF, should be 3.6-4.1 ohms (bottom of page D 24-15 of the WSM, in the "LH-EZK-Diagnosis/Troubleshooting" addendum -- section 24/28).

I don't think that is an adequate test to find out how aged and out-of-spec a MAF is, however. It is also really hard to get an accurate resistance measurement for that low a resistance-- just touching the probes together usually reads half an ohm or so.

There's nothing really wrong with Mark's old-school tuning for a race car-- just fiddle with the FPR until the mixture is about right from 4000-6500 at WOT, that's the operating range. It's going to be awfully hard to get a street car running nicely doing that however-- as soon as you want to drive part-throttle there are too many variables for a simple screw-adjustment. But the current no-start is something different.

mark kibort

actually it drives great part throttle. better than other stock cars Ive driven. no surging, no lag, no problem on start, ever. what I have done is actually pretty mild as a mod. just a fuel pressure mod. the MAF and other components don't know what the displacement is, and can adapt very well. just as the AFM on the Ljet did on the 84 going from 177hp to 290hp and uping displacement to 5 liters keeping fuel ratios in the safe range was pretty easy. surprisingly, all the part throttle operation was good too.

thanks. I also don't want to chase my tail (or he chase his) and just start replacing parts without understanding what is actually wrong. first glance it seems like, certainly there is a leak in the damper. that could be the age old problem of his hot start issues (intermittent over the years) . the no start could also be an issue there, but overnight, the initial start should be possible even with a leak. the fuel pressure being low with pump running is concerning, and points to a fuel pump or the RRFR. easy check I would think. check the source line for pressure at the damper and if that's good then its the regulator, or some injector is just flooding the cylinder to release that much pressure. im going to visit the patient today.. so thanks for the ideas!

what does the "30/19" is that the lb injector ratio of stock vs what he has?

do you think the damper can let enough fuel out of the lines, to cause the pressure to be almost non existant in the fuel rail? plus, we disconnected the lines (vacuum) and no fuel was shooting out, so its kind of pointing to the fuel regulator or fuel pump. going to bring my stock regulator over to his house and swap it if we get full pressure at the damper input for the main fuel line.
thanks guys!!! (my fellow 928'er thanks you for the input as well).

and by the way GREG, im no expert in fuel systems. just using some logic in diagnosing this issue. my tuning has been very simply just making sure the fuel ratios are safe. seems to work, since the capability of the stock system seems to be more capable than most give it credit for. In the early days, wasn't Joes and Mark's cars tuned this way?? 520hp with PVC pipe MAF adapter (4" pipe with the guts of the MAF stuffed in), bolted to a one off CF intake, with Home Depot tubing and stock ecu, no chip mods and a fuel regulator. and you bash on my techniques?

mark kibort

I just visited the patient! Now im more confused than ever with this one.

put a pressure gauge on the fuel rail...
occasionally used the fuel relay jumper to assure pressure in the rail.

here is what happened.

with the relay out and jumper in , the pressure gets to 45psi and stays there.
it doesn't start. interestingly, turn off the starting processs and the pressure goes down to 0 in about 4 seconds.
with the relay in, I doesn't start either, but the pressure doesn't rise above guage reading "0".

while trying to start, it seems to have arcing showing sparks at the disti.

Then, I starts to catch. in fact, it starts running, blowing all sorts of black smoke out the back, sounds like its running on 4 cylinders, but there is no pressure showing on the gauge. so , I quickly pull the fuel pump relay and put the jumper which gets the pressure to the normal range, but it wont start and do that again. a few times earlier , it would almost catch and the pressure went near 10 to 20psi.

now, I start to look at wiring, and I notice the LhJetronic box is really warm. im thinking , its the LHbox. it was rebuilt by Rich A a few years ago and maybe its got some issues. should the LHjet box get that hot to the touch... I think something is cooked!!

saw the fuel coming out of the damper only with use of the hand held vacuum gun to pull pressure on the nipple of the damper, but its really small amounts of fuel. with full line pressure, nothing comes out of the damper. don't think that could be more of an issue than just hurting warm start.

one time there was a very loud buzing noise from under the intake. could that thermo time switch have an injector in there or something that could buzz? didn't to do that all the time, just once.

mark kibort

oh yeah, while it was barely running, we had No TACH signal at the dash at all. it all points to a possible ECU LHJet issue, no???

little help from the slewth experts. anyother things we can test?

hb4

I'd swap out the fuel pump relay for starters. Sounds like the contacts are burnt causing low voltage at the fuel pump. More problems than that of course, but one step at a time.

mark kibort

we are well beyond that... we went back and forth with the relay. its working fine.. you an hear it engage at start up.

somethings up where there is no fuel pressure when it was nearly running. something is up where there is no tach read out too.
its almost like the injectors are being held wide open .
its really bad............. the only thing that makes sense right now, is that the LHjet could be really bad.... aftrer all, why is the box super hot to the touch. I don't think the LJjet box should have that much temp in it from just starting the car on and off for a while.