Engine Sputtering after 351W swap(EFI)

[Dark_5.0]

What is your fuel pressure set at? With your combo and 30# injectors your ideal pressure will be really low.

I bet you are running super rich.

[Dark_5.0]

Lets assume with your very mild 351 that you are putting out 300HP.

At 300HP your ideal fuel pressure would be 20 psi WOT.

At this point you are way over injected.

[bluethunder87]

Really?!...I read that I should be running between 43-60 psi. I think that its currently at 48psi.

[jimberg]

You should be at 39psi. My car is putting down 345 hp to the rear wheels with 30# injectors and fuel pressure set to 39.

[Dark_5.0]

Originally posted by jimberg
You should be at 39psi. My car is putting down 345 hp to the rear wheels with 30# injectors and fuel pressure set to 39.

Are you crazy?...........Your combo is way stouter than his @39 psi with 30# injectors he would be really rich.

He is not making much more than 300HP at the flywheel.

he is way over injected period.

Not to mention his fuel pump wouldnt support 30# injectors at 39 psi now would they. The answer is no.

Your response baffles me.

[bluethunder87]

Actually, I should be running close to 400 hp(at least according to all the numbers)....hopefully!

[Dark_5.0]

Originally posted by bluethunder87
Really?!...I read that I should be running between 43-60 psi. I think that its currently at 48psi.

With the stock pump your not even capable of sustaining 48psi under WOT.

[Dark_5.0]

Originally posted by bluethunder87
Actually, I should be running close to 400 hp(at least according to all the numbers)....hopefully!

Not with what you listed. And definitely not with the stock pump.

Not even close.

[bluethunder87]

ok....so you're telling me that the 30 lb injectors that I have are too big?

[Dark_5.0]

I cant be sure with out being there but with what you have listed I would be very surprised to see you make much over 300 HP.

48 psi is way too much fuel pressure. 48psi with 30# injectors is enough fuel to support 470 HP.

You need a bigger pump for sure. And IMO even then your ideal pressure will be a little over 20psi which will give you a poor spray pattern.

You can get by with the 30 # injectors until you upgrade the engine but you will be stuck with a poor spray pattern because of the low pressure.

[jimberg]

Dark_5.0,

His computer should be able to compensate by reducing injector pulse length based on feedback from the O2 sensors. If he were to lower his fuel pressure, he'd get a bad spray pattern, like you said, which would cause inconsistent and incomplete combustion. That could lead to more problems in fuel management since it could cause false O2 sensor readings. As you probably already know, air/fuel ratio is controlled by the computer and not what the fuel pressure is set at. If his MAF sensor is calibrated to match his 30# injectors, he should be okay. 48psi is too high which is why I brought up how much HP my engine puts out. If I can get 345rwhp with 39psi, he clearly should be able to support whatever he's getting at 39psi. Maybe he can even drop it to 30psi to see if things improve, but I wouldn't go any lower than that.

Bluethunder87, when you drop your fuel pressure to 39 or even 30 psi, be sure to reset your computer and then let your car idle for about 10-15 minutes so it can relearn it's idle.

You should really upgrade to a 155 or 190lph fuel pump depending on what your plans are. It seems that the 155 is good for at least 345 rwhp.

[bluethunder87]

I will try this once the fuel pump comes in. Thank you very much guys for the knowledge!

[HotRoddin]

Originally posted by bluethunder87
Ok guys, fritz does have a valid point about engine break-in period. Thanks, fritz.

Heres some food for thought on this subject .. read the article its very interesting, i think its logical and the theory fits with the experience i've had putting motors together. I've had a couple engines that i had no time to break in ... they got run hard right from the get go ... both were the longest lasting best sealing motors i've ever had.
http://www.mototuneusa.com/break_in_secrets.htm

[Dark_5.0]

The fact of the matter is the car is smoking black which means it is running rich.

Now that we know he was attempting to run 48psi we know why the motor was cutting out.

Yes the ecu controls the pulse width but when he stepped on the gas the fuel pressure was sky rocketing up to 48 psi WOT which would cause the rich condition he is having.

Just cut back the fuel and it should run great.

Sorry for calling you crazy Jimberg

[PKRWUD]

I have to agree with Dark 5.0 on this. I think the main problem is that the injectors are too big. The bigger your injectors are, the lower the pressure needs to be for a near stock application. The lower the pressure, the crappier the spray pattern, and the crappier the spray pattern, the worse it will run. This is why it's important to get the right size injectors.

In any case, with the pressure that he's running, when he goes to WOT, it's going to dump way too much fuel in there, and the result will be black smoke, crappy performance, and eventually fouled plugs. Add to that a .045" plug gap, and you're just asking for problems.

Of course, that's just my opinion.



Take care,
~Chris

[FritzDaKat]

Originally posted by HotRoddin
Heres some food for thought on this subject .. read the article its very interesting, i think its logical and the theory fits with the experience i've had putting motors together. I've had a couple engines that i had no time to break in ... they got run hard right from the get go ... both were the longest lasting best sealing motors i've ever had.
http://www.mototuneusa.com/break_in_secrets.htm

Yes it does make sense, but thats only in cases where the shops are using the "latest and greatest" (Relative to the past decade) in machine tool technology and where micro-polishing can be performed effectively. Theres plenty of shops out there running with the same equipment their Grandfather's had used and doing excelent work with it, provided of course the traditional rules on engine break in were followed.

However, I think when it's time for a rebuild Im going to have to take it to one of the shops using top notch gear and modern techniques, of course Ive still got a decent amount of miles left in it. ( Sitting at 96K now)

[bluethunder87]

Hey guys, thank you so much for the wealth of knowledge. For I am just learning the ropes of building engines and fine tuning them. I just replaced the fuel pump last night and when I get finished with some minor work that I have been doing I will fire her up again and try the advice that has been given. I will post the results once I'm done. Thanks!

Thank you also for supporting your military!