alritzer

Hi guys, I finally got my S5T2 rebuilt (since July of 2013). It started right up and ran pretty good for about 35 minutes. Then it just died. I thought it was a bad gas problem so I drained the gas and refilled the tank.
The engine starts pretty easy but only runs for about 15 seconds and then dies. If I pump the gas pedal I can keep it running but as soon as I quit pumping the pedal it dies. If I restart it right then, I will have to pump the pedal to keep it running.
If it cools off a bit, it will run OK for about 15 seconds.

thanks, ashley

pfsantos

iTrader: (1)

That's weird (yeah, you already thought that). Almost as if the AFM is unplugged, but you said it ran for 35min. before, so that couldn't be it, unless the plug doesn't have the clips and just happened to undo itself after the first time it ran.

Not sure if the S5's have the yellow fuel jumper female plug near the AFM. If it does, I'd jumper it and see if it runs easier.

Check fuel pressure. Also, how's the fuel filter? Almost seems like it's building pressure to start, then can't keep up. So another reason to check the fuel pressure.

alritzer

I've already tried jumping the test plug for the fuel pump and I checked the AFM as outlined in the FSM.
The fuel pump is new, Walbro 255 GSS341. I checked it anyway with a fuel pressure tester. Pressure inline is about 38psi, max pressure was about 60 psi. The only thing that didn't appear correct was the hold pressure. The hold pressure is supposed to be above 18psi after 5 minutes but mine was below 10. The reason I disregarded that reading is because I was using an Autozone tester and wasn't sure about the accuracy.

gxl90rx7

iTrader: (1)

i had a similar problem and it ended up being a vacuum leak, the cold start map was rich enough to get it to idle even with the leak, but not when warmed up

alritzer

OK, thanks. I'll check for leaks.

alritzer

I had a friend check for vacuum leaks and not one was found.
Does anybody have any idea why it runs ok for 15 seconds and then dies? I have the idle set way up to around 3000 rpms. So, it starts pretty easily, runs at 3000 rpms for 15 secs or so and then dies, unless the gas pedal is pumped repeatedly.

ash

w0ppe

The autozone testers aren't actually all that bad unless you're using incorrectly. Most of them are just rebranded normal tools.
You have spark obviously since it runs, check timing?
You have air flow since it runs, and the turbo / engine should pull in as much air as it needs, no constrictions or leaks (seems like you did this already).
You have fuel, but are you too rich or too lean?
If none of the above, let us know to move on to the next step.

pfsantos

iTrader: (1)

I'd still recommend checking the fuel pressure. Both teed into the system, and dead headed to the pump. You can sometimes rent the F.I. pressure testers.

Really seems like it's starving for fuel.

alritzer

I had already checked the fuel pressure with the tester inline and dead headed. Inline pressure with the key on and fuel pump checker jumped is 38psi.
I just checked the pressure again with the gauge inline. When the engine starts running the pressure drops down to 28 psi. As soon as the engine stops, the pressure goes back up to 38 psi.

alritzer

.

pfsantos

iTrader: (1)

Oh, yes, missed that part. Can't add much more, but any chance the fuel lines are reversed?

lastphaseofthis

iTrader: (8)

You say you pump the pedal to keep it running.. what if u just hold the pedal steady at say 3500 rpm instead of jabing it and the rpms boucning.

Can it ibe made to stay steady with steady throttle?

alritzer

Nope, if I try to hold the rpms steady it will die.

Should the fuel pressure drop down to 28 psi with the engine running? It actually drops more when the rpms are raised.

bumpstart

depending if s4 or s5 then 38 base pressure sounds about right, and it will drop when engine vac is applied
( the stock ECU will deny the FPR a vacuum signal for a short period after starting )

on a well tuned engine idling around 900 rpm then usually this will be about 18 inch Hg
,, or about 9 psi.. so 28/29 sounds about right if your engine is pulling this vacuum

it should only go lower than that when in decel ,, when vacuum is higher than 18 in Hg

cone_crushr

iTrader: (18)

Ash...again? Your RX continues to test you. Please elaborate on this answer about vacuum leak checks. What exact leaks checks were performed? Did they spray carb cleaner or smoke? Where was it sprayed? around and under the UIM? around the fuel injectors, intake tract? This issue is worth more effort since a thermally induced vacuum leak seems a likely culprit. How can you do a proper vacuum leak check with an engine that can''t be made to run at any constant speed? Will it run at 4000 RPM? 5000?

w0ppe

If everything is good, I'd say to check the ECU mapping, but sounds like you're running stock anyway. You could also have a bad build that fell apart after 35 minutes...

alritzer

We used carb cleaner and sprayed around and under UIM and checked all of the connections to the fmic.
My friend checked for leaks while I kept the engine running. If I keep the rpms around 3000 and continually tap the gas pedal it will continue to run, just not very good. I can keep it running in the 2900-3100 rpm range by short fast pumps on the throttle.

alritzer

Yep, ecu is stock with the rtek 1.8 chip, 550/750 injectors and fmic. I really doubt the build fell apart, but if it did, it won't be rebuilt again.

I've had this 7 for 3 years and its never been more than a mile from the garage. The engine has been taken out and reinstalled 4 times. Long story starting with a used engine that was total crap.

alritzer

I found out that if I unplug the TPS the 7 will run a lot longer and smoother. It actually ran about 15 mins by adding more throttle every 30 seconds more or less.It might have run longer than that.
So,I figured I had a bad TPS so I swapped it out and nothing changed. Runs the same way with both TPSs.

pfsantos

iTrader: (1)

A common error is to adjust the TPS when the throttle is not completely closed. You not only have to warm up the car, but ensure the fast idle cam (at the back of the TB) disengages.

Unplugging the TPS causes the computer to ignore it and use a 'fail safe' value.

I'd try adjusting the TPS.

satch

iTrader: (1)

The default value for an unplugged TPS is full throttle so obviously your car runs better when the ECU thinks the engine is running at full throttle.

What were the condition of the primary injectors before install? Have they been serviced before being used. If not, then one possibility is they are somewhat clogged.

And are you using the fuel relay and resistor located under the AFM?

alritzer

OK. Thanks satch. When this first started I thought that I had bad gas. About 10 minutes before it died I had added 5 gallons in gas. Then, after it quit running I noticed that the gas was more orange then usual. I drained all of the gas and refilled. Maybe it was too late and one of the injectors was already plugged.
All four injectors had just come back from Witch Hunter before the problem started.

pfsantos

iTrader: (1)

Did you find out what the orange fuel was?

Did you prime the pump after putting the right fuel to take the old fuel from the lines (yellow fuel connecter you jumpered before)?

Have you adjusted the TPS, properly, engine warm, fast idle cam released and the throttle completely closed?

alritzer

We aren't sure why the fuel was orange but I know one of the gas cans was used for diesel fuel last winter for a torpedo heater. Nobody remembers if the diesel fuel was rinsed out. My dad says he "thinks" the gas can was clean.
I'm not even sure diesel fuel is orange-ish.

The engine is definitely getting clean gas now and the tps has been set correctly.

ash

MickeytFC

iTrader: (1)

Rtek 1.8 requires 720cc or higher injectors all around. Change out those 550s. Its possible this could be doing something weird to the fuel system although doubtful. If you do get it running 550s will lead to a very lean condition and you'll just blow it.