Hey guys.. I am currently tryin' to get my 96 T/A A4 Lined out and having quite a few problems doing so. Any help you guys can provide would be great...

The First problem I am having is that the car is hard to start at times.. Cranking times anywhere from 3 to say 7 seconds (I know that doesn't sound like much but actually count it out.) Hardly ever starts like it should.

Now... I do have a Fuel pressure gauge in the car as well as an Aeromotive AFPR. I have the AFPR set at 48 PSI when the system is dead headed (No Vacuum on the Regulator) which leaves it at about 39 to 40 at idle. I actually prime the fuel pressure a few times by cycling the key and the car is still hard to start. Something odd that I have noticed is that as soon as the fuel pump relay shuts of the fuel pressure drops to zero within probably a total time of 10 seconds. Should the fuel system hold the pressure or allow it to bleed off? Is this bleeding pressure my hard starting problem?

The Second weird quirk about my car... I have an AEM wideband Air/Fuel Gauge. Driving down the road completely normal. Not going WOT or anything, just driving like a normal Joe Schmo the gauge will go from hovering around 15.0 to 1 to hovering around 11.2 to 1 for a few seconds, then goes back to 15.0 to 1. This happens at random intervals, foot applying pressure on the gas, no pressure on the peddle, doesn't matter. Just does it when it pleases.

The car also dumps a very large amount of fuel if you tap the gas pretty hard at idle, the gauge goes all the way to 10.0 to 1 and bounces back after a second or 2.

Why is my car dumping this extra fuel in for no reason? Is it in the computer tune?

Third - The car has a funny idle problem sometimes it idles great - other times it hunts for an idle by about 100 RPMS very rarely more. I've actually killed the car backing out of my level driveway when I let off the gas. Just an annoying quirk that I would like to resolve.

Fourth is a general question about a Pyrometer - What is the Normal Idling temperature for an LT1 with Shorty Headers and No Cats. My gauge reads around 800 Idling and sits around 1150 to 1200 when I'm just driving normal down the road.

How do I acurately use this gauge for tuning? What do various temperatures mean?

I would greatly appreaciate any help you guys could provide. I am tryin' to get my car lined out for a snort of nitrous but with these problems.. I don't feel safe spraying it.

 

Sounds like you have a leaky injector(s). I would pull the plugs and check them out. I had 2 leaky injectors on my car. It was hard to start and ran crappy.

Lee
96 Z28

 

I'll tackle the first two of your questions.....

Number 1: My car is doing the same thing and always has. It's either a leaky injector or your fuel pump. With KOEO your fuel pressure should around 43.5psi +/- 2psi and it should hold steady. If it drops fast its usually the pump. Mine jumps to 40psi, then drops fast to 10psi then drops to 0 which explains the long start problem...the same problem you have.

Number 2: As far as your wideband goes, I'm sure its normal for the car to dip into both sides of the spectrum. The PCM is always adjusting fuel management to strive for that stoichmetric setting. Also, it was my understanding the AFPR does nothing for these cars due to the fact that the computer will adjust to whatever fuel pressure you throw at it.

Hoep this helps.

 

Yep.. My fuel pressure does the exact same thing yours does.

I've had a guy tell me there is a check ball in the pump itself that is to hod the pressure when the pump shuts off and that that check ball goes bad sometimes. Can anybody verify this?

As far as the Wideband O2 goes.. I knew it should oscillate a fair amount around stoich (Say from 14.0 to 15.5 ish) when in open loop (All sensors inputs taken into account by PCM) and should go richer when in closed loop (Minimal sensor input use) but it's almost like my Car is going in and out of Closed loop just driving down the road. Is this possible? Should I hook up a scan tool and see if this is whats going on?

You are correct on the AFPR - It won't do squat. I just put it on there so it would be easier for me to install my Fuel Pressure gauge.. I also like to have all the goodies.. However useless they are.

Thanks for the quick replies guys!

 

Yes, there is a check ball in the pump, when this goes bad it allows fuel to drain back into the tank when it shouldnt(our problem) however, you cant replace this individually....you gotta replace the whole pump. This is why I ordered a racetronix pump today before it goes out for good and leaves me walking. As far as seeing if your car is going in and out of loops, get a cable and software(freescan will work fine) or a scanner and have at it.

 

So if I order the Racetronix Setup this should rectify the problem?

I need to upgrade my fuel system for the Spray anyway. Which system did you go with from Racetronix? Got a link? Did you get the Hotwire setup or no?

 

I would agree ya have a pump problem. Change your pump and then see what happens.
To check your injectors,pull the rail, with the injectors attatched turn your key on and cycle your pump until ya have pressure and see if any leak.
Your EGT guage is used to measure your max exhaust temp after a pass (1300-1400*)to adjust your timing and fuel.Using it at cruise I don't think will tell ya anything that is important as the computer is gonna put it where it wants it.

 

There are three things that can cause the fuel pressure to drop too quickly on shutdown. 1) The check valve in the fuel pump can be bad, as mentioned above. 2) The injectoers can be leaking. 3) The fuel pressure regulator may be leaking.

You can check for a leaking AFPR by looking for fuel in the vacuum line. You can find leaking injectors by pulling the rails up and pressuring the system and looking for drips.

The sudden richening of the mixture might possibly be traced to a TPS sensor that has a non-linear output. The voltage should increase smoothly from closed throttle to full throttle. If the sensor has a spot where it suddenly changes voltage, that might be enough to fool the PCM into thinking you're opening the throttle, and it richens the mxture. Take your scanner, and watch as you slowly open the throttle. Voltage should change smoothly, with no spikes.

It's also normal for the PCM to richen the mixture when you suddenly open the throttle at idle.... in that way it responds exactly the same way as the accelerator pump would on a carb.

On the EGT gauge, its not possilbe to just pick the optimum temperature and say that's where you tune it to. The EGT is a good measure to watch AFTER you tune it, and can see what the exact temperature is when the tune is "on". That way you know where it should be, and you can detect changes in mixture by changes in EGT. But its not a way to "tune".... just a way to monitor. 1,200degF just cruising down the road seems a bit extreme though. I don't see that kind of temps until I'm WOT under heavy load. But that's the problem.... each gauge is different, based on which cylinder you are monitoring (mine is on #7) and how close you have the thermocouple to the exhaust port.

To track down the idle problem, put a scanner on it, and watch how the IAC counts respond to the out-of-spec idle condition. Might indicate if the IAC is responding correctly, or needs to be cleaned. I had a wierd situation where the idle speed would pick up a couple hundred RPM and then back down, and tracked it down to a loose grommet on the vacuum line at the power brake booster.

 

This is awesome you guys are giving me all kinds of Ideas to check.

I've already decided to go ahead and replace the fuel pump. It needs to be done anyway.

I checked the injectors when I put my AFPR on. No leaks there. So that leaves the pump.

Injuneer - I know what you mean by checking the counts on the scanner, but what should they actually be doing, going up or down with the idle? I am using a snap-on scanner. Also, that makes alot of sense on why the vehicle goes so rich. I just never thought it should go that rich.

(Edit) - You may be onto something regarding the vacuum leak. I also have no control over where the A/C vents blow in my vehicle. IF there is a vacuum leak these go to blowing on the floor correct? And will not change no matter what position the switch is in?

Another question, Who would you guys recommend for a mail order tune on my PCM?

 

For PCM mail order - MadZ28 or pcmforless

I don't know which way the HVAC flapper doors fail to when they lose vacuum, but I suspect they will default to floor only. Shoebox would know. There's a vacuum connection from the passenger side of the intake to the HVAC controls. There is a check valve in the system, and there is also a small vacuum canister in the passenger front fender. Any of the components in the system could be leaking. Whether that's the problem is another matter, but its worth checking, simply by blocking off the vacuum port on the intake manifold. Shoebox has detailed pictures of the components and connections on his website.

http://shbox.com/1/4th_gen_tech1.html

The IAC counts should respond to try and control the idle. If RPM goes up, the IAC counts should come down to bring it back to spec. If rpm drops below the programmed idle speed, counts will go up to try and control it. Counts should be in the range of 20-40 at idle.

 

Gosh this car is being the biggest pain in rear... I've had 4 Fourth Gens and this one is by far the biggest pain.

I am planning on putting the car on the scantool tommorow to see what is wrong with it. Hopefully I can track something down.

I put it on the scanner today for a little while and tried to see if any sensors were REALLY out of whack... I found 2 that were out of whack but I don't know if they are really wrong or if my scanner is just a pos.

My MAF was reading 0. So was MAP. The only thing that gets me is all the other sensors were reading normal. And what are the chances of 2 sensors not working at all.

MAP also had a voltage of -.55 but was reading Zero for pressure.

What would cause both of these sensors to read zero unless they really are broken?

This latest revalation could definately be the cause of all my problems.

I am going to check for 5 volt reference INTO the sensors tommorow and if it is there I guess I am going to replace them.

Another odd addition to my idle surge... It only does it IN gear.

As far as my fuel pump situation. None of my problems were corrected with the addition of an Inline Pump. So.. I am assuming I do still need a pump. But it is not the root of my problems.

 

Only the MAP sensor has a +5V reference. A voltage of 0.55V should produce a MAP reading of about 5.5"Hg (~18kPa). If you have less than 14kPa, you should be getting a code/SES for low MAP voltage. Check the harness connector on the sensor.... they have a habit of drying out and crumbling, producing erratic readings.

The MAF sensor requirea +12V input from the pink wire on the harness connector. Key on, engine not running, see if you have 12V on that wire. There is a frequent problem on the 97's with that wire breaking back in the wiring harness, resulting in a dead MAF sensor. Maybe the 96's are starting to show signs of the same problem. The MAF sensor output is a variable frequency. If your MAF sensor is reading "0", you should have a code and an SES light.

 

The MAP actually showed a negative 0.55. Which I wouldn't figure as being possible.

So do you think that I have a bad MAP or that my scanner just isn't communicating correctly?

Where in the harness are the MAF sensor wires breaking? Random Places? Or is there a specific place.

Also.. All of these voltages and values were with the engine running. If that makes any difference.

 

Also.. I do have a code but it is a (I believe) P0412 I think that code is related to my AIR Pump delete though...

 

Is your SES light on or isn't it? If you had an MAP voltage of minus 0.55 (engine running or not), you should have an SES light. If you have an MAF reading of "0" (obviously the engine needs to be running for a non-0 reading), you should have an SES light. If you don't have a light, the PCM is not seeing the same data your scanner is seeing, and that's sort of impossible since the scanner reads the PCM. What kind of scanner are you using?

The pink wire runs through the harness, serving several different power users. The MAF is the last on in the series, and its the only one that loses power.... but I don't know if anyone has found the exact place where they break. Generally, you end up needing to run a new wire all the way from the fuse.