Doin a fuel pressure test on my 305 tbi... it bogs out and drops rpms at 40 mph.. if I do a fuel pressure test at idle and it is indeed low fuel pressure at 40mph will it show up as low at idle???

also does anyone kno the correct psi for the pressure?...and where do I do the test from?

 

I want to say its 9-13 but it may be 11-13. The fuel PSI doesnt ever change from the fuel pump. The only thing that changes is the amount of fuel being let in by the FPR. I had a similar issue on my 89 and did the test and found pressure to be like 6-7 so changed the fuel pump and no more issues since. Speaking of that its about time for another fuel pump to go out. I change the damn thing like every 2 years.

 

My bad forgot to add in that you will have to undo the fuel line on the driver side and screw in the adapter. then connect the line to the adapter and there you go

 

Try changing your fuel filter first. When I first got my car like 12 yrs ago it would bog after too much RPM and it was the filter. My fuel pump went bad about 4 yrs ago, I put in a Walbro and been good ever since.

 

Is there a test port on this thing?

I have this fpt http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_Fuel-Pressure-Tester-Kit-Actron_9030328-P_N3388_T|GRP2018____#fragment-3 will it work?

I think its suppose to be checked before fuel filter?

 

Are you refering to the fuel line attached to the throttle body closest to the driver side?

 

Look at the pic, next to the alternator you can see the T adapter (that one has a black plastic cap on it) for that gauge , though it does not seem to be included with the gauge in the link you posted.
https://www.thirdgen.org/forums/atta...i-dsc08259.jpg

edit: add FP related link https://www.thirdgen.org/forums/tbi/...-pressure.html

 

Yea I have the T adapter for the gauge , Im not 100% sure where to hook it up tho... I have no garage or jackstands so I cant lift up the rear to get to the fuel filter...where else can it go?

 

Next to the alternator on the top line (feed line), is a easy spot to ad the T. Like shown in the pic in post #7.

 

thanks man Im out of state right now but will do it that whay when I get home

 

The adapter in that Actron 7817 kit can also mount to the fitting @ the back of the TB itself.

Like the fitting I posted for DSGx, for a remote cabin gauge.

I've used that actron setup for years & plumb wore one out while working on many different rigs, even my new one is lookin a little ragged.

I mostly post this at the late date, for other readers so they know what we are talking about.
& can find the right stuff with a link.

Gauge kit: http://www.summitracing.com/parts/SUN-CP7817/

Adapter: http://stores.ebay.com/TBIPARTS_TBI-...=p4634.c0.m322

 

my camaro runs great thru all rpm ranges with lots of power. However, when the engine is cold, it takes about 10 seconds for it to start. I can turn the key and wait, it will start right up.It has been suggested to rebuild the diaphram in the throttle body, because pressure is bleeding back when the engine sits. Does this sound right to anyone else?

 

NO. TBI systems don't hold pressure.

 

With the engine off and key in the run position the fuel pump runs for about 2 seconds, after the 2 seconds the pump stops and the pressure drops. The pump starts again at the same time as the key is moved in the the start position.

If the diaphragm is bad, fuel will leak out of the fuel pressure regulator.

 

I rebuilt the regulator, still have the same problem. If i put a splash of gas into the tbi it fires right up and runs beautifully. I have full power thru all ranges.

 

First Guess: Fuel pump relay circuit. No fuel pressure until the fuel pump is triggered by the oil pressure switch, which requires cranking long enough to build oil pressure.

 

The fuel pump relay switch is bypassed, as soon as I turn the key, the pump is running.

 

WHY would you do that? Damned unsafe in a collision--the pump won't stop pumping fuel, and the car--and you--burn to death in a bath of gasoline.

 

Thanks, I'll try that. you must be referring to the pinto and mustang scenario. But back to the problem at hand.

 

Fast355 talked about brazing up the fuel pressure bleed-off port in the regulator. I have never done this and not quite sure which port it is but he claimed his van no longer suffered from the TBI long start up syndrome.

Your fuel pump could also be getting weak. I noticed when I upgrade my pump to a TPI one the car start much faster... But still slow compared to a properly setup carb or newer style fuel injection.

 

Maybe, but I don't know. The power is perfect thru all the rpms. A weak pump would make it a bit sluggish. Besides, it's a throttle body, they don't need near the fuel pressure as tpi.

 

Is there a wat to set up a primer for my throttle body so it will start quicker when cold? Once it has started, it restarts fast thereafter.

 

I already told you what to do in my post above if you want faster start up time for your TBI.

BTW, when I upgraded to a TPI pump I noticed more power throughout the whole power band. If the pump is not putting out the volume it should be, performance will suffer. Regardless of psi required to run.

 

Never noticed anything like "the TBI long start up syndrome" in normal ambient temperatures.

Every engine with TBI, I have came across started up just as quick as any other type of well maintained fueling system.
I do have experienced that by -20° C temperatures, WOT is required to start these TBI engines, but in these situations the same happens with many other fueling systems from various manufacturers.

As to what could cause such a long start up syndrome in normal conditions, could by many things and maybe couple ore more little things combined.
If it was happening on my set up, I would go over every ignition and fueling related components, as last resort probably even look at the fueling tables and adjust accordingly.

 

I just got the car back from the shop. I had two brand new batteries go dead. The first was replaced, the second I charged and took it to the shop. They couldn't find a drain and couldn't find a problem. But there again, once you get it to start, after that it starts on about 1 revolution. Also turns out I knew more than the shop. The mechanic couldn't believe that the battery may be low enough to allow it to spin fast yet not enough current to activate the ecm. I can splash a little gas into the throttle body and it will fire right up. And my second battery is new and fully charged.

 

I never had this problem at -20C. Just the normal "long" TBI start that I've had with any TBI I've owned/worked on. Now I did have a problem starting my car in -40C and forgot to plug in the block heater over night. It started, didn't like it but it did run after 20 seconds of cranking.

 

good thing the fuel didn't freeze

 

Then the TBI cars you've "owned/worked on" are very different than the one's I have experience with. Good luck.

 

TBI starts are not even comparable to any MPFI, espescailly those with a cam/crank sensor. Full stop. I'm not trying to be rude here, but I would suspect Switzerland does not have many (US) TBIs. I have owned 3 TBI vehicles, all of which the TBIs were rebuilt, fuel pump changed + pressure checked, starters rebuilt, tuneup, etc etc. Also worked on the bench for 2 years before I got into the elevator trade and saw/worked on a large number of TBI vehicles. NONE of them start like a newer vehicle. Perhaps our ideas of a "long" start differ. A properly setup carb literally catches with a flick of the key, even in -20c. Newer MPFI is pretty good. TBI is at the opposite end of this spectrum.

PS: I would just like to add that I am refering to STOCK TBI stuff. My modified TBI running EBL does start a lot better than stock. I'm sure the high torque, gear driven mini starter helps as well.

 

I think you need to get yourself a good Stopwatch.