No Fuel Under Boost??

[240Timmons]

Greetings fellow 944 fans! I'm new to the forums and very frustrated with my 951, as i'm sure we all have been!

I've been poking around on the forum and I haven't found my specific issue fully addressed but i'm sure it's been discussed many a time, so if this is a redundant repost, please kindly point me in the right direction


My Issue: *I HOPE YOU'RE READY TO READ...TAKES BIG BREATH*
Car goes completely lean after a few seconds of boosting (kicks, pops and looses power)


Back Ground Story:
I purchased my 86 951 a few months back. When I test drove it, it would only boost to about 9 psi and ran at the correct AFR's, but it didn't have very much power. After taking it home I discovered 3 large boost leaks (hole in the cold intercooler pipe and two rubber boots were torn)... After I fixed the boost leak the car would (and still does) after a few seconds of boosting, run lean enough to not support combustion. Even when I run it at the same 9psi or lower it acts like it runs out of fuel.
The fuel pressure feels EXACTLY like it's running on an accumulator and after a bit, it runs out of umph until you take it easy for a few seconds (10 or so) fuel pressure seem to "recharge". *NOTE: the issue may not be fuel pressure but that's what it feels like*The car seems to run better and not run lean as quickly once it's up to operating temps.

The car idles and cruses smooth and at the correct AFR's (maybe a little lean) but anything over 0 manifold pressure it will lean out after a few seconds. Keep in mind, the AFR's will remain correct at even 6000rpm as long as it's below 0psi. The car is also very very sluggish when cold with horrible throttle response.


Here's What I've Done So Far:
I've drained the fuel, installed new fuel screen, new fuel pump, new fuel filter, new stock fuel pressure regulator, pulled all 4 injectors and cleaned them. Rebuilt the waste gate and shimmed it, boosts to about 14 psi now. I've tested and cleaned the stock MAF (temp sensor or door) and it checked out perfectly. Tested all the coolant temp sensors, I found the one w/ the two open prongs to have an OPEN with NO RESISTANCE so I used a variable resistor to simulate a working temp sensor (300 ohms) at the applicable temp but it made no difference. I've used a smoke machine to locate vacuum leaks, the only one that i found was a minor leak through the throttle body shaft. I took out the DME and the KLR and cleaned the connections, the tube had no kinks. The DMEhas a tuned chip (MAX HP KIT 95 DME III) but lindsey racing told me that is was just as good if not better than their tunes. I also installed a new DME/FUEL PUMP relay (no difference)

I'm at a total loss and i'm quite discouraged by this car.. It normally takes me 30 seconds to diagnose and issue but this car has me STUMPED.

Any help would be GREATLY APPRECIATED!

my two last ideas are:
Possible low voltage to the fuel pump
or Bad DME or KLR

[Techno Duck]

First off, are you sure the vacuum line for the fuel pressure regulator is connected to a port on the intake manifold?

I would check your fuel pressure as this will save you alot of trial and error. You should see about 36psi at 0 manifold pressure. Then you should see 1 psi increase per psi of boost.

Monitoring your fuel pressure while running can be a pain, but you can get creative with a temporary solution.. .





Assuming you do not see expected fuel pressure at boost, as you already figured i would check your voltage at the fuel pump at full load.

[DannoXYZ]

How are you monitoring AFR?
What brand/model DME & KLR chips do you have?
Can you keep it floored and redlined if you set max-boost to 9psi?

[240Timmons]

Thanks Tech Duck:
i'll do that.. I actually intended on doing that but I couldn't find the correct adapter for my fuel pressure gauge. Do you know what size is it that connects to the front of the rail with the cap and ball?

Dan:
Right now i'm using the crappy narrow band that the PO installed. It's pretty vague but it tells me enough that i know that it's running so lean sometimes that it can't read it... but regardless of having a AF gauge, I can feel/tell when i'm running lean, rich or no fuel.

chip in the DME is (MAX HP KIT 95 DME III)

I cannot keep it floored at 9 psi.. or even 1psi with partial throttle. it will run at 13-14 for a few seconds (and it feels great) then it falls on it's face..



what really confuses me is the fact that it would run rich enough under 9 lbs of boost when it had all of those boost leaks but it leans out when it doesn't have any leaks

[DannoXYZ]

Hmm, if it's really a fuel-flow issue:

1. Test total fuel-flow volume. Remove cap @ end of fuel-rail and connect hose into bucket. Turn car on or jumper DME relay to turn on fuel-pump. You should be getting massive flow like 2-gallons/min.

2. Check fuel-filter

3. Test FPR as TechnoDuck mentioned. Pressure should be about 36-38psi @ idle. Then increase by psi per psi of boost. So with 10psi boost; you should have about 48psi fuel-pressure.

Monitor that fuel-pressure when you floor it and it dies. Does fuel pressure change just before or after the stumble?

[Techno Duck]

The fitting needed for the rail is M12x1.5 . Also your fuel pressure will only be 36psi at idle if you have the vacuum off of the fuel pressure regulator. With vacuum you will probably see closer to 30psi.

I wouldnt really trust anything that narrowband gauge is telling you as the resolution is just too low to tell you anything useful.

It is normal to run rich with boost leaks. The DME is injecting extra fuel based on what the air flow meter is telling it. With the boost leaks this air is being lost and not making it into the cylinder. The DME doesnt know this so its still injecting the extra fuel. The opposite happens with vacuum leaks, your sucking in unmetered air that the DME does not know about.

[Xaerran]

I haven't seen you mention this yet, but have you checked the plugs? It is sometimes an easy way to verify the rich/lean scenario the A/F gauge is giving you.

[240Timmons]

Originally Posted by Xaerran

I haven't seen you mention this yet, but have you checked the plugs? It is sometimes an easy way to verify the rich/lean scenario the A/F gauge is giving you.

I'll do that, but run it lean so very little that I doubt it will tell me anything besides a normal AF ration.. but i'll look

Originally Posted by Techno Duck

The fitting needed for the rail is M12x1.5 . Also your fuel pressure will only be 36psi at idle if you have the vacuum off of the fuel pressure regulator. With vacuum you will probably see closer to 30psi.

I wouldnt really trust anything that narrowband gauge is telling you as the resolution is just too low to tell you anything useful.

It is normal to run rich with boost leaks. The DME is injecting extra fuel based on what the air flow meter is telling it. With the boost leaks this air is being lost and not making it into the cylinder. The DME doesnt know this so its still injecting the extra fuel. The opposite happens with vacuum leaks, your sucking in unmetered air that the DME does not know about.

^^this makes sense.. and i've thought of that.. but what doesn't make sense is that the fuel system could clearly keep up w/ 9 psi.. b/c regardless of it having a boost leak or not.. 9psi in the cylinders is still 9psi (boost leak or not). this is what's confusing b/c it makes me think that the air flow meter isn't keeping up or something.

thanks for the fitting size, i'll look for one locally first.. and I understand that I need a wideband.. i've always hated this narrow but the fact of the matter is, it's still telling me that i'm falling flat on my face under boost. once I get this issue fixed, wideband is next I had a wide band with the car I just sold, I just didn't think to pull it out :/

Originally Posted by DannoXYZ

Hmm, if it's really a fuel-flow issue:

1. Test total fuel-flow volume. Remove cap @ end of fuel-rail and connect hose into bucket. Turn car on or jumper DME relay to turn on fuel-pump. You should be getting massive flow like 2-gallons/min.

2. Check fuel-filter

3. Test FPR as TechnoDuck mentioned. Pressure should be about 36-38psi @ idle. Then increase by psi per psi of boost. So with 10psi boost; you should have about 48psi fuel-pressure.

Monitor that fuel-pressure when you floor it and it dies. Does fuel pressure change just before or after the stumble?

i'll check total fuel flow, good idea. also, the filter is brand new.

[DannoXYZ]

Sounds like a leak that's opening up under boost. Take apart the intake from the turbo-outlet to throttle-body and inspect every single piece of rubber. The thin intercooler hoses can split underneath the hose-clamp. Also the conical hose going into throttle-body can pop off as well since it has a very thin clamp and clamping area.

[240Timmons]

Originally Posted by DannoXYZ

Sounds like a leak that's opening up under boost. Take apart the intake from the turbo-outlet to throttle-body and inspect every single piece of rubber. The thin inter-cooler hoses can split underneath the hose-clamp. Also the conical hose going into throttle-body can pop off as well since it has a very thin clamp and clamping area.

It doesn't have any leaks, I replaced all of the rubber for the inter-cooler piping b/c they were almost all leaking.

[240Timmons]

Update:
So, today I was working on my A/C and recharging it. I got it blowing nice and cold but when I was about to take off the a/c gauge lines I noticed I heard a hissing sound from under or near the air box.. so i fumbled around and picked up the air box to see if there were any vac lines underneath and the whole MAF JUST FELL OFF! So MAYBE that's why it's acting like the MAF isn't working! i'm really hoping so.
When I was messing with the intake J-tube, I found out it was leaking and torn in 3 spots... And a I tore 3 different hoses/lines... And I broke the coolant tank. I swear I wasn't being rough with it, everything just seemed to be brittle and old :/ so it looks like i'll be spending about $300 tomorrow. Crossing fingers! I'm keeping an optimistic attitude

[DannoXYZ]

Ah... so the AFM wasn't connected to the rubber J-boot? That's quite a leak!

That explains the super-lean mixtures when it stumbles, the turbo's sucking in air after the AFM and the AFM is registering zero airflow. DME injects zero fuel. Damn old rubber and plastic parts are so crispy at this age. Get a metal J-pipe, custom-fab it if you need. Saves you a tonne of troubleshooting later.

[240Timmons]

Originally Posted by DannoXYZ

Ah... so the AFM wasn't connected to the rubber J-boot? That's quite a leak!

That explains the super-lean mixtures when it stumbles, the turbo's sucking in air after the AFM and the AFM is registering zero airflow. DME injects zero fuel. Damn old rubber and plastic parts are so crispy at this age. Get a metal J-pipe, custom-fab it if you need. Saves you a tonne of troubleshooting later.

Well this doesn't guarantee anything bc the meter was still hooked up and reading... It's just that it could have been leaking some amount that it wasn't enough air flow to register the boost. I think I'm just going to order a MAF kit instead of spending money on stock parts

[DannoXYZ]

Yes, go with the Rogue M-tune. Best value for the buck in upgrades. Infinitely adjustable and tuned via laptop just like an aftermarket EFI standalone EFI system. You set the actual fuel & ignition values in the chip itself, rather than use piggybacks like other systems.