Fresh Re-build but need help - Studdering and Acceleration Problems !

[fortwayne240]

Yet another Post about problems... and I have searched, but with no solutions....

Ok, here we go....A fresh rebuild, all new EVERYTHING, all new timing chain and components, CP Pistons, Eagle Rods, Tomei Head gasket, yada yada... my basic setup is as follows

2871R .64 a/r300zx maf740 tomei injectors255 walbro fuel pump264 intake cam272 exhaust camgreddy intercoolerAEM Fuel press. regulatorENTHALPY ECU Tuneetc...

I am having a studdering problem right around 4000 rpm's and above durring wide open throttle..... right around the time I hit full boost. (right now @ 9 PSI)

As I watch my AEM wideband, it starts off at about 11.2 AFR and holds steady.... as I get to about 400 rpm's it suddenly drops to right around 16.0:1 and then goes to 17.0:1 and then the car starts bucking and jerking all over the place.....

I have checked the TPS, coolant temp sensors, the CAS, the spark plugs and coils, the wiring, the MAF sensor, fuel injectors, fuel pump pressure, timing, checked for boost leaks, etc... al check out according to the FSM.

I believe that the problem is something with the fuel system, such as fuel pressure or fuel injectors. I have tried correcting the problem using my S-AFC all the way up to 50% and it still happens..... any suggestions ?

I am going to go out right now and disconnect the S-afc completley and see if that is causing any problems....

Help is appreciated, so thank you in advance....

[fortwayne240]

Bumpity Bump Bump

[fortwayne240]

Also wanted to say that I just checked the battery charge.....

it holds 9.6 volts at idle, but when I rev the car either with a load (in gear) or sitting still the voltage drops to 8.1 volts.... I believe that this may be the problem.... a bad alternator....

Any comments?

[doridori23]

Holy poop I am amazed it even starts at 9v. What is happening is that your fuel pump cant supply the fuel you need thats why you are leaning out. GET THAT BATTERY CHANGED BEFORE YOU BLOW UP YOUR MOTOR! That being said after wards look very hard at you alternator. you should have 12.7v with nothing (I mean motor) running. At idle you should see s light increase to 13.2 to 13.4 ish and above 2400 RPM you should see 13.8 - 14.2 v and hold that to redline. Some alternators will make up to 14.8v but it isn't necessary and actually not recommended (Why do you thin they make voltage regulators ) If you see no change in the voltage at all then your alternator took a crap also. I have used USDM 240sx alt's for the Silvia motor without making a goofy bracket or anything of the sort. The last one we ordered the volt ref harness with the new alternator to make the wires 100% and get them a little longer to make change out easier.

[fortwayne240]

Well, another update. The alternator is changed out, and I changed the battery. The alternator is supplying the battery with 13.8 volts but the S-AFC says that the battery power at the ECU is now 10.1 volts. I am thinking that the alternator and battery setup is working correctly, but there is something wrong with the wiring, power supply to the ECU or the grounds for the ECU. I will be checking all of these items here today.

[doridori23]

Have you ran the motor since changing the alt and batt combo? I would like to see this fixed as you spent a lot of money on a block and if they installed everything they should have checked this. If you installed it you are getting a crash course in hotrodding. Trial by fire isn't always fun but it is the fastest way to learn!