Subject: Re: '88 Turbo Z stumbling when cold
Date: Thu, 25 Mar 1999
From: zdoc <zdoc@yosemite.net>

Tom writes:

Hi ZDoc,

I have an '88 300ZX Turbo White Limited Edition with just over 93,000 miles. The previous owners kept the car in immaculate shape, and since I bought the car in November, the only problem I've experienced with the car is that it hesitates at part throttle when cold, and it doesn't stop until the engine is almost completely warm. It has a noticeable loss in power
from about 1500-2400 rpm, after which the engine surges with power. It will also run fine with more throttle, but I'm not real interested in pushing the motor until it's fully warm. I have tried using some Berryman's fuel injector cleaner, which eliminated the problem, but only until that tankful of gas was gone. After that, the problem came right back.

The previous owners have an identical Ltd Edition, and it does the same thing. Is this common with the VG30ET motor?

Thanks!
Tom

Doc replies:

Hi Tom, Doc here, it would seem that your situation may be attributable to several possibilities. First of all have you been getting the fuel at the same station? It is highly possible that you are running into too much alcohol (MTBE) in the blend. If I read you correctly, after putting Berryman's in the tank the problem subsided. With the MTBE in the mix the engine must get up to heat to efficiently vaporize the fuel. This situation is compounded be the engine management controls that are trying to lean the mixture out in closed loop since the O2 sensor is a major input sensor in this mode.

Another factor could be the use of non factory spark plugs. The factory plugs are NGK Type and many shops use Bosch Platinum's since they are a cheap plug, but the trade off in performance is not worth the savings. Likewise with the Splitfire Brand too. Thirdly with 93K miles in the "Z" it may be necessary to recalibrate the EFI system. When your vehicle was manufactured the standard for the fuel was approximately 115 BTU's per pound, and with the advent of the Reformulated
Fuel it is approximately 95 BTU's. The effect is that many engines are trying to cope with lower energy potential energy while still at the greater calibration. Consequently they are running too lean all the time. Unfortunately this contributes to higher pollution since the leaner running increases the HC in the emissions too.

Have you replaced the EFI fuel filter recently? With it removed use a clean paper towel and carefully blow back through the fuel filter in the reverse direction onto the towel and inspect the debris. Pink or brown indicates that the alcohol (MTBE) is adversely affecting the coating inside the fuel tank and is possibly starting to remove some of the solder from inside the tank. Black indicates that the fuel pump is starting to go away. Since the pump is immersed in the fuel the MTBE takes away the lubricating properties of the old blend that we used to have and wears out the pumps much sooner than the original designed life span.

You can get a transmission funnel and install it in the gas tank filler and start the car and listen to the sound of the pump
running. If it sounds like it is straining or erratic in the sound then you may need to further investigate with an appropriate pressure test of the system.

In conclusion, there are several things that you may consider as less expensive options. I hope that this helps you in some of the decisions to solve your situation......

ZDOC OUT

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