Truck is at the dealer now with a P1093, just 1000 miles after a P1093 and EGR valve failure repair. Nothing on the original warranty repair concerning the P1093, they simply cleared it I suppose. The code was thrown stock with 1000 miles on fuel filter this time driving 70-75mph. I cleared the code and it came back at 60 mph immediately. I just received a call from the service advisor stating they need to install a new fuel lilter on my truck because the aftermarket ones don't flow properly and it is at 3" vaccuum. Waht is the magic vac number??? They are wanting $142.00 for a filter install and diagnostics time. After I talked to the advisor for a few minuites and asked him about the trouble tree for the P1093 and the high pressure return valve in the fule rail he backed up a bit and said they can not check it until I pay for the fuel filter? What can I tell him to get this right?

More details:

Mileage on truck.
Tuners.
Exhaust.
Any other mods?

The first thing they do is replace the fuel filter. $142 is ridiculous. You can do it yourself in 30 minutes.

You can of course let them replace the filter, and when that does not fix it, request that they eat that for diagnostic time.

Aren't all Dmax (stock location) fuel filters made by Racor? How could an aftermarket fuel filter made by Racor and badged as brand xxx flow any differently than a fuel filter badged as Racor made by Racor? Hehe sounds like the service dept might be reaching on this one.

10k miles on truck

i do have the edge j/a, but it was not installed at the time the cel light came on and had not been installed for 3 days.

no other mods. truck had been stock for nearly 600 miles when it limped.

bad part is i know the dealer is reaching, but they have to follow the "trouble tree" and the first required step for this code is replace the fuel filter at customers expense if the code does not reappear in 10 miles. it is crap!

The problem is the pop off /pressure relief in the drivers fuel rail.I just come in from the shop on an 05 that keeps setting this. If you snapshot fuel rail pressure it slightly low on accel but he problem is usually when you decel. The rail pressure will spike to 24-26k psi and the relief pops and returns the fuel to the tank.Once this pop, it doesn't seem to close till rail pressure drops under 6-7kpsi.
To test put a hose on the relief and road test with a container stuffed in the corner by the brake booster.Use a larger container because when it pops it it really leaks.It should really should never pop.
The trucks I've seen don't seem to act up till hot. The fuel temp is usually above 140*
Gm's fix is to replace the LH fuel rail with the relief in it. This truck I just tested, I replaced the fuel rail earlier today.There seems to be a problem with the reliefs.I will try to talk with engineering tomorrow and see whats up.
I've got several snapshots and very well documented test results and this will get rectified.Be patient

The problem is the pop off /pressure relief in the drivers fuel rail.I just come in from the shop on an 05 that keeps setting this. If you snapshot fuel rail pressure it slightly low on accel but he problem is usually when you decel. The rail pressure will spike to 24-26k psi and the relief pops and returns the fuel to the tank.Once this pop, it doesn't seem to close till rail pressure drops under 6-7kpsi.
To test put a hose on the relief and road test with a container stuffed in the corner by the brake booster.Use a larger container because when it pops it it really leaks.It should really should never pop.
The trucks I've seen don't seem to act up till hot. The fuel temp is usually above 140*
Gm's fix is to replace the LH fuel rail with the relief in it. This truck I just tested, I replaced the fuel rail earlier today.There seems to be a problem with the reliefs.I will try to talk with engineering tomorrow and see whats up.
I've got several snapshots and very well documented test results and this will get rectified.Be patient

Sorry but I have a dumb question as usual. Is this the same system that was used on the LB7? If so could it just be programming on the LLY is more sensitive to this than the LB7?

Thanks for you efforts.

lakingslayer the lb7 doesn't have thesame relief valve that midwest is talking about it is located in the back of the drivers side rail. i agree with midwest i just changed my valve alone not the whole rail because gm only offers the rail as a assy. but from bosch you can get just the valve. i could pretty much throw 1093 at will i know it's only a day but can't throw them so far. i think the rail is like in the range of 300.00 us and the valve is like 125.00 us

No the system is totally different. This systems feeds the LH rail from the front and then feeds the RH rail out of the middle of LH rail to the front of the Rh rail. The pressure relief is in the LH rail @ the rear. The fuel pressure sensor is in the Rh rail.It's not a programing issue. The problem could be aggraveted by programming due to increased fuel flow but not the problem. I have several stock trucks that do this. The relief can pop when fuel pressure spikes but should close @20k or so.I feel the window of operation is too large(25-8k).Pop @25 reset@20k psi

How hard is it for a semi competent DIY to replace the valve? I'm worried that since it's on the rail it's under a good amount of pressure. Also if it's a fairly easy job do you have a P/N and contact at Bosch for one? These P1093's can potentially be dangersous for us and other drivers.

It is fairly easy iI can get you one.

Those of you reading this post and have p1093 DO NOT automatically assume you have a pressure relief issue. If you have a big Program it IS very likely that you will have low rail pressure on hard acceleration.This is where monitoring fuel rail pressure is critical. If it is low on accel and the relief has not poped you WILL need a lift pump.If you experience this stock, it is probably the relief. It's simple to check the relief as I described before.
I tried to get someone in engineering today and no luck. The guy I talked to said if the relief pops replace it. He claims it is a one time only relief and should be replaced. I disagreed and ask him then why does it pop 800-1000 above operation range.The original documents on the LB7 Was 29400 for relief. He had no answer and got pissy.I said if fuel rail is at 23500 @ wot and you lift the throttle and fuel delivery instantly stops pressure will spike. (like water hammer in grandma's house), and he had no comment. I,ll try again tomorrow.

I have replaced several LH fuel rails for this concern as well.:exactly: The problem is the pop off /pressure relief in the drivers fuel rail.I just come in from the shop on an 05 that keeps setting this. If you snapshot fuel rail pressure it slightly low on accel but he problem is usually when you decel. The rail pressure will spike to 24-26k psi and the relief pops and returns the fuel to the tank.Once this pop, it doesn't seem to close till rail pressure drops under 6-7kpsi.
To test put a hose on the relief and road test with a container stuffed in the corner by the brake booster.Use a larger container because when it pops it it really leaks.It should really should never pop.
The trucks I've seen don't seem to act up till hot. The fuel temp is usually above 140*
Gm's fix is to replace the LH fuel rail with the relief in it. This truck I just tested, I replaced the fuel rail earlier today.There seems to be a problem with the reliefs.I will try to talk with engineering tomorrow and see whats up.
I've got several snapshots and very well documented test results and this will get rectified.Be patient

Dealer replaced fuel rail yesterday. Today set 1093 code. Pred on kill, from about 45 mph wot to about 70 mph, at let off coded. Same old story.

All this stuff is scary to new truck owner...I have 800 miles on mine and I hope none of this happens with mine...Does it seem to happen more if you put a tuner chip in?

All this stuff is scary to new truck owner...I have 800 miles on mine and I hope none of this happens with mine...Does it seem to happen more if you put a tuner chip in?

It does seem to be more common with power adders. There have been a few with the problem running stock though.

8shot can you monitor actual rail pressure? Was it low on accel? Did the code set when you got back on the throttle AFTER a decel or While decelerating. Tim

Don't know if it was at let off or when i got back into it. I let off at 70ish, then rolled into throttle and truck fell on its face. Then i saw engine light. Pluged in pred and had 2 codes. P0101 which pops up once in a while and 1093. Cleared codes and stood on it . Could not get it to happen again. Aso had a full tank of fuel. Can i check rail pressure with pred?

I have the fix for the relief valve poping. Its not Gm approved but it fixes 1093 codes due to relief valve poping on decel 100%.The great thing it cost only one thin dime. I will reveal later. Checking legal. Be patient Tim

I had another 1093 today. I hit the hammer and spun the tires hitting 3rd gear. When I hit 5th it started bursting bad at about 80mph. I slowly let off the hammer. No problem. I slowed to 60mph and started to do a slow accel to get back up to 65mph. When I put my foot on the peddle I got no power and the CEL came on. Scanned with the Predator on the fly and P1093 code. Erased and went on. This is the second time I did this on the trip after filling up. I was on the freeway yesterday going 70mph and I hammered it and let off the throttle at about 85mph and no codes. That was on about 1/4 of a tank. Also no bursting.

You have my attention Tim.

Just put a set of FM100's in and it seems that 1093's are A LOT less frequent, driving 2 days, only kicked in during one trip..

Well.. spill it would ya :)

and what was the "thin dime fix"? I have to be on the road heading to scranton on friday and my local mass dealer dont have a clue yet.. I need this asap..


thanks :)

Is it just a resister?

Sounds to me like he is blocking off the relief valve. High risk?

midwest has been testing it and he says that its %100 working but he has not mentioned anything of it being dangerous or a potential risk.. We'll just have to wait and see! He will release more information after this weekend..

Round three with mine. Just took it in this morning. Truck runs fine, pass a car on the highway at half throttle cel comes on and loss of power. Took it to a differant dealer this time, they brought out the service manager, 2 advisors and 1 tech who brought his tech2 to the service drive. He hooked up and found the 1093 again, manually drove the rail pressures up and they were perfect. He thinks mine is a pressure regulator or the fuel rail pressure sending unit. They will be on it today and let me knw what it is. I also showed them the fuel filter the other dealer said was clogged, his response was that filter looks nearly new. I think I will be getting a refund on that part too. The tech also told me that 6" vaccuum at the service port is not a problem, the injection pump will almost always produce vaccuum at the service port and that the way theyt are supposed to determine fuel filter problems is by driving the rail pressures up and monitoring them. Does all this sound legit? This guy really seemed to know what he was talking about and was quick on his feet with answers and reasonable suggestions.

Question. Will it work on both the LB7 and LLY?

Question. Will it work on both the LB7 and LLY?

LB7's are a whole different beast. Seems that lift pumps really benefit the LB7 tremendously. I think we're pretty much in a league of our own with these 1093's.

First off it will not work on the LB7.As in several post before, it is very simple to catch the regulator.Install a hose on the regulator return and plug original hose.Put a large container by the brake booster and then drive it like you stole it. If any fuel in container it is the relief.

There is also a fuel rail DELIVERY issue with big boxes.This will not likely be adressed By GM but I have a fix.It will be tested on a aurora 5000 LLY this week.
The pressure relief problem is on stock trucks but is worse on trucks with programs because of the increased demand for fuel delivery.With the increased injector pulse the rail pressure falls off quickly so the pcm commands the pressure regulator to lower the duty cycle to increase rail pressure. Normal duty cycle is 30-35%.With big boxes the increased fuel delivvery causes the reguator command to go as low as 18%(max) (the lower the duty cycle the higher the pressure comand) With the regulator maxed out or at least lower duty cycle the rail pressure spikes much easier when you decel and the relief pops.Not a programming issue just The result of.

Remember if you drop rail pressure on accel only it is MOST likely a fuel delivery issue. If it happens after decel and then reaccel, check the relief.
More info after indy. TIM

That was a very good explanation IMHO of how the fuel system is regulated. Thanks

I have a 2004 DMAX with the 1093 problem. Truck has 8100 miles and is bone stock. After a day and a half of diagnosing at the dealer with the multiple page trouble tree and info for the GM tech line, the problem pointed to the injector pump and not the injectors. Pump is being overnighted and we shall see if it fixes the problem when I get it back this weekend.

I may be possible its the pump but I really doubt it. Hope in your case they're right.

Got mine back on friday from the dealer, they flashed it and boobie trapped it for a performance box. The tech smeared silicone all over the connectors to tell if a box was being connected. The turbo seems to spool quicker and it makes a few more pounds of boost. They could not identify any other problems. Hooked onto my trailer (about 8500 lbs worth) and headed out for the weekend. 100 miles of trouble free towing to the first wife induced stop. Took off out of their parking lot and boom, cel comes on right in the 1-2 shift and straight into limp! pulled over and checked fuel filter for water, none. cranked truck back up and cel still on, but it was out of limp. Truck never limped again all weekend, but I was very easy on it and cel went out saturday evening on the way home. It seems like mone only does it at 1/4 tank and under and only during a shift. Im am at a loss with this truck, I have been a chevy man for 10 years and I love the truck but it is becoming very frustrating.

hey midwest whats the plan here? GM is saying now the vendor is out of stock untill late August... I need this fixed by late today):h ots aggravating as F%^K I disconnected the Edge last week and it almost seems to be doing it more often now.

any clues?

Do your own diagnosis with the return hose and see if it is actually the refief. If it is it can be bypassed very easily but not the proper repair. Parts shortage is why I have not released my fix because I modify the stock relief and have cut apart several to figure out and have no cores to send anyone. The relif should never pop unless a pressure control problem. I have several heavy moded LLY's with the relief blocked and no issue but not something joe blow should do. I'll post more as I get more parts. Tim

The "tuner" P1093 is not related to the "stock" P1093. Two entirely different situations.

This may have been gone over before..... But what is so different in the LLY fuel system from the LB7 fuel system?

Do your own diagnosis with the return hose and see if it is actually the refief. If it is it can be bypassed very easily but not the proper repair. Parts shortage is why I have not released my fix because I modify the stock relief and have cut apart several to figure out and have no cores to send anyone. The relif should never pop unless a pressure control problem. I have several heavy moded LLY's with the relief blocked and no issue but not something joe blow should do. I'll post more as I get more parts. Tim

How do you go about blocking the relief valve?

With my d-max out of the shop for the 1093 problem, they found it was the injector pump. Through the trouble tree, pressure tests, fuel flow rates etc, it was found that the pump was only puting out 116kpa instead of 160KPA. They said the pump could not maintain pressure even when programmed form the tech 2. SO the pump was replaced. Truck seems to run fine and I will keep you posted. It was not the injectors which is what I thought. :ro)

I hate to say this but they are not short of supply unless you need say 40 or 50 valves. I just order 10 more from the supplier.

any new info?