Hi,
got a mostly stock 1985 L98 with the 4+3. It starts and runs absolutely fine hot an cold. No bogging, no hesitation, backfires, whatsoever. Fuel system, all sensors etc. are tuned up. IAC and TPS are new and adjusted the right way. The injectors and chip are the original ones.
The car sees some drag racing now and then. I use a ZEX wet nitrous system with a 125 hp shot and Hoosiers on track days. For nitrous usage initial timing is retarded 6 degrees as stated by ZEX.

The only problem I have: The car runs very good ( low 13´s with a best of 13.16 in the quarter mile on spray ), but leans out immediately after shifting into third. The mixture won´t fatten up at the 3 to fourth shift.
This happens with and without nitrous usage.

I´m located in Germany ( still no speed limits at our Bavarian Autobahn ). The car accelerates very good, even in third, but leans out while accelerating. After accelerating, the Vette feels like throwing an ancor at 134 mph. I feel the car would go into high 12´s with a fatter 3 and 4th gear mixture.

Question is: Is it injector time? They ohm out nice at 12,6 all 8. But does that keep them from shortening at revs beyond 3800 rpm? I feel I should do the fuel pressure at driving test by taping the gauge to the windscreen to make sure the new Walbro 255 is ok. To compensate for the problem I raised fuel pressure to 50 psi, it looks a bit better, but that´s not the right way.
What you think? How can I know that new injectors would be the right move?

AFR is measured with a wide band O2 sensor mounted directly beyond the original O2 sensor at the driver side exhaust. I can read what´s happening with that little gauge.



Racetech gauge

Bye Erik

 

My stock 85 injectors would not support 400 hp without being bumped up to 50 PSI. Would lean out at high RPMs. Since every time you shift to a higher gear you are increasing load and taking in more air, it would only make sense that the injectors would be maxing out. What is your injector pulse width at on a scanner when this happens? Use an online calculator, multiple your Base IPW by 2 and enter into the calculator. Technically 80% is max duty cycle but you can squeeze more.

 

becareful not to crack your windshield when closeing the hood with the hose in the hood.
email Jon at fuel injection connection. look to the right for their add. good deals.

 

Why are people so hesitant to do anything with injectors? They would do everything around the car, bump up pressure but leave the injectors? Next thing is dyno tuning or even datalog tuning. Never understood that.

Ohm test tells that the coils are OK. Doesn't tell fuel volume or spray. Get the things tested ever few years. Never ran an Ohm test on any of my injectors. All it does it give you a FALSE sense of security that all is well because the test came out good.

If you are running that kind of power, why not just change the injectors for better and larger ones and set the tune. This way, you can set the car to run WITHOUT the bottle and it runs perfect. Maybe get something from Moates which can allow you to run 1 tune for NA and one tune for nitrous?

 

Thanks for the replies.
What i forgot to mention is the strange acting new TPS.
We´ve done the IAC setting, than the TPS was adjusted to 0.54 V at idle. Idle is perfect now.
But when i go to WOT I only get a 3,87 V readout. Is it possible I have a bad new TPS, so the power enrichment isn´t engaged by the ECM due the lack of voltage? Or is 3.87 V enough to get the PE started?

Bye ! Erik

 

When mine did that, the throttle cable and cruise control cables were backwards. The throttle plate would not open fully.

 

No, that´s not the problem, we have checked this.

 

3 wires. One ground, one 5V reference and the other is the output to the ECM. Where did you get this 3.87V readout from? DId you check it from the ECM or just the DVOM? Also, did the reference read 5V? Do that check with 1 probe on the 5V line and the other on the battery ground.

 

3,87 V measured at the two top wires with a DVOM. 5V reference at the third lowest wire. Grounds looking good.

 

I would do the fuel pressure gauge taped to the windshield. Easy, quick and peace of mind. As far as the 3.87 volts at the TPS, it seems like it would be enough for PE. Just guessing. (I'm running a Megasquirt) I wouldn't suspect the injectors yet. You are basically stock and have a wet kit, so I don't know what the other guys were talking about. I would reach out to Cliff Harris or Bjankuski.. I'm sure there are others but I would trust anything those guys say about your ECM tuning....
You said that your car leans out in 3rd and also feels like and anchor was thrown out at 134 mph. I'm not sure you can go 134 mph in 3rd or if these things are relevant.

 

No sorry, it starts to lean out in third, but keeps accelerating. You shift into 4th and it keeps acceleraring....until 134 mph. At this point it feels
like you were stepping heaviley on the brakes.
Snowy roads these days in southern Germany, so I have to wait for the fuel pressure test until the local Autobahn is clear of snow and ice. I´ll keep you informed what is going on further

 

You are on the correct path by checking fuel pressure, this needs to be verified before you make any mechanical changes, or tuning changes. Since the car is stock and you are running a wet NOS system the stock injectors should be fine. What gear ratio do you have? My assumption is you have a 3.07 ratio and if you are not using overdrive that would mean you are at 5340 RPM at 134 MPH which would explain why the car feels like an anchor has been thrown out. A stock L98 makes most power around 4500 RPM and by 5300 RPM it is way beyond it power band. If you could provide the gear ratio and RPM at 134 MPH I could provide more feedback.

 

Thanks ! It´s the 4+3 with Dana 44 3.07 rear gears. The point is last year I drove 149 mph at a flat bit Autobahn, without problems and without the feeling the car was throwing an ancor. Both speeds 134 and 149 mph were read at the speedo. Who knows what it really was.....
But related to this situation, I asume that something is going south today. Maybe it is the MAF slowly dying now ( bothrelais were changed last summer ).
My plan is the fuel pressure while driving check to make sure the new fuel pump an filter are doing fine. I will screw in new injectors in the same stock size, so the electronic tune in stock form should work fine. Should the problem persist, I will try to get a MAF from a german buddy, to test and make sure, that´s not the problem. Next step would be to go into the tune on the chip.
I need a scanner and are asking myself what would be the best equipment for real time scanning with later extensions for burning a chip. The Ostrich stuff sounds hot to me.
First I need snowless dry roads

 

-What was your RPM and the speeds in question?
-If you get a scanner not the MAF readings when the car starts to lean out.

 

Were you running NOS during any or all of the runs?

 

With and without N20, it makes no difference. We even pulled the ZEX mixture control box to really make sure it is delivering fuel, not only N20. Works fine.

The racetech display is mounted in the cockpit, so I can read it while driving. At idle, in 1st and 2nd gear the LED it at the max power point ( see pic ), even if I am at 5000 rpm. In 3rd it is falling immediately in the red zone, till no light is shown. Not good for the L98 and not good for the time slip.

Is it possible,that the injectors are going into lock up because of high rpm and 50 psi fuel pressure? But then again why are they working fine in first and second gear? This again leads my thoughts to the MAF.




Bye !

 

Could it be that you are in higher rpm and/or needs more fuel at that level? Why 50 psi? I thought the stock is 43? Is this the new injectors we are talking of? Ask around but check the pulse width and see if it drops at the 3rd gear area. See if others know what it should be.

 

This seems like a strange situation, and like I mentioned before you need to check fuel pressure before anything else.

The car has no idea what gear you are in the tune is not adjusted by the gear you are in. I have a theory but it may not be the issue, please check the fuel pressure first.

Is it possible that you have a miss on one of the cylinders when you get to a longer pull (longer pulls create more demand on the ignition system) like third and 4th gear. If you have a miss the WB sensor will show lean because there is excessive air in the exhaust due to the miss. I have seen spark plug gaps that are too large or weak ignition systems do this. what is your spark plug gap? I would set it at .025 for nitrous use and N/A use and see if the problem goes away.

 

Look through this vid. Sorry that it is quite long but if it is snowy there then you may not have much to do anyway.
Our US Army trucks were limited to 100 KPH and we were very jealous when guys like you and the bikers would fly past us back in the 80s.
https://www.corvetteforum.com/forums...-when-hot.html

 

Thank you, a very useful vid !
But you US-Army boys ever had the best US-Cars around in Germany. I remember hanging out in Stuttgart at the Rock Fabrik. Many soldiers were there.
Same goes for Munich back in the day. I bought my other car from a lady at the US-Army in Munich, as she went back to the States she left the car, which was my luck back in ´88. Know what.....the Trans Am is still mine 32 years later



The old T.A.





Wife in the Vette

Bye !