I have a rebuilt 383. It was rebuilt with SCAT forged 383, zz409 cam, dart 200cc heads, mini-ram, 58mm tb, 30# injectors, msd distributor and coil, and headers. i haven't been able to check the fuel pressure yet but when you slowly bring in the throttle it will rev just fine but if you give quick WOT, it hesitates for about 5 seconds and finally will rev. i can get a good idle if i adjust the screw and the TPS sets about .73 volts. I've tried to go lower with the idle to around .54 volts and it just isn't enough to keep the engine running. It has a PROM built to specs of the engine and timing is set 6*btc. Does this sound like a weak pump? Also I can hear the pump prime when I turn the key to on but I also hear the pump turn off when I shut the car off. Should I hear the pump turn off as well???

 

If it is the stock fuel pump then it might not be able to keep up with the engine demand. Only way to really tell is to use a fuel pressure guage and see what happens when the stumble occurs.

 

Did a little investigation and finally put a fuel pressure tester to it. With the line disconnected I have the PSI set to about 45 PSI. When I connect the vacuum line the PSI drops to around 35-38 PSI. It also has a intake backfire to it. I talked to Jim at TPIS and he said that if the intake is backfiring then it sounds like it's running lean. It only does the backfire at quick WOT squirts. When I turn the key off, the pressure drops from 45-20 psi in about 1min. but it will hold at 20 psi for a while. So I don't think I have a bad diaphragm or leaking injector's but should it drop from 45-20 that quickly, is that normal? Now when I hooked up to the aldl and was monitoring the rich lean condition. It was most of the time always lean so does this really sound like a weak pump? I have a Holly 255 on the way so do you guys think this will solve my problem? Thanks a bunch

 

Well i guess you are running a vacuum referenced regulator. Easy way to find out is disconnect the vacuum line from the regulator and plug it this way you should always have 45 PSI wether in gear or in park. If the problem disappears then you need to up the fuel pressure so you have 43 to 45 PSI when in gear and not in park or neutral.

 

Also just re read your post. You should adjust the fuel pressure with the vacuum line connected and the engine idling. This way you get your pressure at idle and it increases as rpm's increase.

 

Should the pressure go up when giving throttle, b/c when I see the gauge the pressure decreases when I give it throttle but it's only sitting still. Does the vehicle need to be under load in order for the pressure to go up? Again I see it decrease to around 35-38.

 

what are you running for a chip? a stock chip has a 22lb injector constant.

 

It's a custom chip build from TPIS for 30# injector's.

 

So i took a datalog today and here is what I find. With no VSS input, if you if it throttle, the EGR Duty cyle comes on. I thought the EGR duty cycle should only come on with VSS inputs. It's still stumbling when give WOT sometimes. I'm not really great at knowing what's doing on with this data so could someone take a look at this for me and tell me what the ECM is doing? The program I used is TTS datamater.

 

nobody? really could use the help

 

I found out that my fuel delivery system (combination of pump, filter, injectors, pressure regulator) could not keep up with engine demand by observing a fuel pressure guage during a dyno pull -full throttle, under load, max demand on fuel delivery system-. Can you minitor pressure while at full throttle in high gear? Either by guage indication during dyno pull, or, as I used to do, connect a guage, tape it to the windshield so you can read it SAFELY while punching the gas in high gear. If pressure drops off significantly, then one or more of the above mentioned components is restricting fuel delivery. I replaced the pump, filter, and regulator, then maintained full pressure at the fuel rail during the next dyno pull.

Bill

 

sounds like you have the same combo as me. I run a walbro 255lph fuel pump along with 30lb injectors. I don't care what anyone says, when you order a chip for your car, they tend to be off by a bit. I went that route originally,and then ran my car on the dyno, and it was rich as hell. I later dynotuned it and perfected it and gained 50 horsepower. So I don't know if its in the chip? But usually Jim is very helpful with helping one out

 

Joe, i was hoping you would chime in since we have about the same. I sent Jim that datalog and I'm waiting to see what he says. What should my fuel pressure be at WOT? I haven't been able to take it on the road and check it under load but sitting still if I go WOT, it stumbles for a second or two and then will finally catch just like the first post says. Also what vacuum should I normal have at idle, with my data log it should around 51-55kPa at idle? I think I may have a vac leak from the seal that meets the block to the manifold b/c I have a oil leak under pressure and I saw today that it looks to originate at that place.

 

Couldn't view the log but it sounds like you need more AE in the chip.
This is the equivelent to the Accellerator pump on a carb.
If your sustained power does not seem to drop off at high revs, I'm guessing you have the fuel avaialable its just not being commanded to be there when you stomp it initially. With a combo like that it would be best to learn how to tweak it yourself to see the best results out of it.

 

the fuel pressure on my car is 48

 

agreed. i was gona say AE, u need more. i had to up mine alot from stock. im close to you on ur specs. 383 HSR, 195cc patriot heads, XFI280 cam, 30lb SVO injectors, 58mm TB, and im running a walbro 255lph high pressure pump.

also u do NOT adjust the fuel pressure with the vacume line attached, you adjust it with the vacume line disconnected bc this is how it will be when u WOT the car, WOT=no vacume. someone stated that u adjust vacume with the vacume connected. when u set the fuel pressure with vacume off your setting the MAX psi... aka WOT, when the car is part throttle it creates vacume, therefore reducing fuel PSI bc its not needed, WOT= no vacume so fuel pressure is set at max for max fuel.

anyways, i had a hesitation like your saying, kinda like a bog when i would stab the throttle. took a bit of fuel in the lower MAF tables and a bunch of AE to get rid of it. sounds like your issue. maybe you have too much timing down low as well... dnt forget, more fuel means u can usually run more timing, if you have too much timing u can run more fuel bc it will require it. same goes for its opposite... maybe u have too much timing and not enough fuel so just back off on the timing. are u experiencing any detonation/knock?

 

thanks for the input. i've got timing set at 10 btdc, and fp at about 48 w/ vac line disconnected. not real sure on how i would id knock,detonation, can you give some insight?

 

wat i meant with too much timing would mean that down low, say below 2500ish RPMs u might have too much timing in the spark tables is what im saying. if your base is at 10, then make sure the base in the chip is set to 10. idk wat the specs are on the ZZ409 cam but aftermarket cams with more duration like quick ramp up with the timing but its possible to go too far and have too much.

any reason u have fuel pressure at 48psi? bc if your running ford SVO 30lb injectors then ur really running 32-33lb injectors at that pressure and u should adjust the BIN accordingly. not to mention if they are bosch design 30lb injectors then really its a 31lbish injector at 48psi. if they are bosch then set them to the 43psi as stock, a 30lb injector is more than enough for your engine bc my 30lb SVOs are enough for my 383 and then sum.

knock and knock retard can be detected with a handheld reader like a autoXray or if your tuning with tunerpro/tunerproRT/ etc... they all show knock counts and knock retard. it should say it in your datalog under flags or values.

 

I have used TTS datamaster and the first datalog that i took showed my retard pretty heavily and then later I think I changed the FP around and my spark retard was much lower. I'm going to take another datalog tomorrow and see any more results. they are bosch design injector.

 

my car was doing the basically the same thing backfire through intake poor performance out of no where took it out for one drive and then it died on me when i got back to the garage tested the pump and it was DOA put in a walbro 255 and car is right back to full power no more bugs!

 

if the spark retard was heavy then u had too much... adding fuel would help since more timing would require more fuel. but if its still retarding timing then its detecting knock and u need to back down on the timing and fuel ASAP!

rememeber changing the fuel pressure without changing the injector constant in the tune will do nadda. the ECM will reconize the increased fuel from bumping the pressure and with the help of the 02 sensor it will decrease the injector pulse widths to compensate, therefore leaning the mixture out and negating the pressure increase all together.