My car is an 86 NA with a street port, header, catback, cat delete pipe and intake. The wideband 02 is in the stock bung in the header. I don't have a narrowband 02 connected at the moment.

I just hooked up my wideband and the car is running around 18:1 AFR under load. At cruise it seems ok at high 14s/ low 15s. It idles well at around 13.5:1 so I know the wideband it calibrated.

It stumbles and the wideband shows it going rich (could be lean misfiring) between 3500 and 4000 under light load, then takes off and pulls fine to redline. I'm suprised it even pulls that well to redline considering the AFR. This is how the car has ran for the last couple months, so this is not a new problem.

I am getting an RTEK 2.0, so should I just tune this out then, or do I have a problem that I should address? I'm assuming this is a problem I should fix first, so what should I check first?

The fuel filter is 1 week old, so it is not that. AddtionallyI should check pump voltage, and possibly pull the fuel pump and check the sock? If that checks out I should probably get the injectors cleaned I am assuming. Anything else? Any way to actually check the condition of the fuel pump?

 

You don't mention the mileage, but getting my injectors cleaned on my 86 w/ 217k made a huge difference, back when I had the car...

 

I assume that you are running a stock ECU and stock injectors? Have you thrown a scope on to see what the injector duty cycle is? At WOT with an open intake, ports and exhaust you are going to flow a lot of air.

 

Yes, stock ECU and stock injectors.

No I have not yet checked the injector duty cycle. I think I will just send my ECU out to get the RTEK 2.0 installed. It will tell me the duty cycle in the logs, and I can give it more fuel. Is it typical to need more injector with a setup like mine?

So you are saying it could be possible that nothing is wrong, I am just moving too much air with all the mods and need tuning? That seems very plausible, because the car runs pretty good aside from the stumble between 3500 and 4000. I did not realize it was running so lean.

 

Just something to think about, 3800 RPM is what the stock ECU bridges the fuel injectors over.. How that happens is if the primary injectors are operating at 100% (they're not, but the numbers are easier), it switches them to 50% at the same instant it brings the secondaries online... So, what you're telling is that there's a fuel delivery problem the instant that the secondaries are coming online and the primarys are cutting themselves half-off..

It would be good to see what the injectors are doing (rtek), however, it sounds like it's the secondaries that are causing the problem... Just sayin'

 

Yea, I am familiar with how the system works, and the 3800 hesitation. The car cruises below 3500 RPM fine, and it is in the mid-high 15 AFR range. It touches low 16s occasionally, but the wideband is probably faster than the ECU. I know it should be a bit richer in closed loop, but I will go with that for now.

When I hit 100% throttle, the stumble between 3600-3800 is not as bad as it is under part throttle. At 4000 the car starts to pull well, but runs ~17 AFR. At 5500 The car pulls even harder, and pulls that way to redline, still in the 16-17 AFR range. After 4000, the car is always smooth under partial or full throttle.

I have regrounded all the ECU ground pins, and that seemed to make the car drive a bit better. It made the stumble better, but it is still there.

The car is not driving like it has a fuel delivery problem, but I have not checked everything out yet either. Could be low fuel pressure or a weak fuel pump I suppose.

I guess I will know more when I try to richen the car up with the RTEK. If it won't richen up, then I truly do have a delivery problem.

 

i would have a look at the pump sock, but its possible if you're making power the stock ecu just isnt giving you enough injector duty.

 

Do you have a pressure gauge you can tap in and see what the fuel pressure is when it's running? A low flowing fuel pump or a clogged sock could definitely cause it as well (as j9fd3s).. . I think I was mis-thinking through the original problem... I would put a pressure gauge on and check, because @ 3800ish, you'll have two injectors opening instead of one, which means a rather bad drop in fuel pressure if you're not getting enough from the fuel pump...

On my old NA, I was running pig rich all the way through the range on the stock ECU, with all of the mods you had, plus emissions removal. I don't see how emissions would affect this, though.

 

I'm in agreement with you guys. I will pull the basket out of the tank and inspect the pump and sock.

If the sock is dirty, what is best to clean it? Brake clean or contact cleaner?

I don't have a fuel pressure gauge yet. Sounds like I should at least have one under hood.

Is there a good place to put one or should I just splice into the rubber fuel hose?

 

Here's how I plumbed mine in when I checked:

Pull the line off the top of the fuel filter in the engine bay.
Get a T piece for your hose size (I forget right now).
Go from fuel filter with a rubber hose to the T, then connect the fuel line to the other side of the T... The third connects to the gauge...

I just put that there and revved it up and watched the pressure over the range. Pressure gauges are pretty cheap that can display the range we need, so I'd pick up one of those... Unless you plan on mounting it permanently, don't waste your money on a "car specific" gauge like an autometer or something, just stop by the plumbing section of your normal hardware store

 

Great, thanks.

I have a mechanical gauge on my Cobra that replaced the schrader valve on the fuel rail. It is nice when you have an extra port to run it off of.

I'll just get a cheap fluid filled gauge from Summit or Ebay, and I will just plumb it into the supply line as you noted.

What kind of fuel pressure should I expect to see?