TBI Chevy running rich.

1 ox sensor, driver's side, pre cat. 

I'll have to look at the closed/open loop.

Temp readings look good.

Map reads atmo at key on engine off, drops down engine running under vacuum.

What kind of cross counts should I be looking for? Tps looks good, no dead spots, reads wide open.

Fuel pressure reg is fully mechanical, so no electronics there.

I can't think of any other sensors involved so it might be time to look for a mechanical problem.

thundrecougar said:

1 ox sensor, driver's side, pre cat. 

I'll have to look at the closed/open loop.

Temp readings look good.

Map reads atmo at key on engine off, drops down engine running under vacuum.

What kind of cross counts should I be looking for? Tps looks good, no dead spots, reads wide open.

Fuel pressure reg is fully mechanical, so no electronics there.

I can't think of any other sensors involved so it might be time to look for a mechanical problem.

With cross counts it's mostly important that there are some.  less the 5 or so points to an issue but there's not hard and fast number.  Basically it tells you that the system is dancing around stoichiometric and not stuck on one side or the other.

It would also be helpful to know what the Block Learn and Integrator numbers are both in the ranges where the engine seems to be running well and where it's not.

Since you've changed the distributor you can't just check and see if the base timing has changed to check the timing chain but you can grab the balancer and see how far you can rotate the crank before you feel resistance from the cam.  That won't tell you if the chain has jumped but it will tell you if it's worn.  Technically it shouldn't be more than a couple of degrees.

alfadriver (Forum Supporter) said:

Maybe some summarizing should happen...

O2 sensors work, cycle, but are not used for feedback at WOT.  

FP failing would be really odd- I don't know of a pump that fails by adding fuel.

Fuel Pressure regulator rebuilt.  if the signal was bad, it would reduce the amount of fuel flow by a likely reduction of pressure.  

coolant temp sensor replaced

ignition all replaced.

Is this MAF or MAP??  (I don't know, wondering)

Fuel pump dying was part of my theory that this is actually a LEAN issue.

Clogged cat?  At this point, disconnect the exhaust at the y-pipe and try it.  Or use a vacuum gauge on the intake.  

No cats on it. But I have made some progress. Turns out it may have actually running lean. I tried spraying it with some brake clean while it was bogging and it reved right up! I'm gonna check the fuel pressure tomorrow and go from there. It seems like I always get the weirdest problems.

I modified the internal regulator in my TBI unit, and ran an external adjustable regulator.  TBI works best with the correct pressure - too high or too low, and it all goes drunk.

In reply to SkinnyG (Forum Supporter) :

That's a good idea.  IIRC the range is somewhere around 12-15 psi, and I've read that it likes to be in the high end of the range, like 14ish.  Any details on how you modified to add an external adjustable regulator?  I might like to do that on my 454. 

There's not a lot of mods one can do on a TBI system....there's a slightly better exhaust crossover and a high-flow cat will help.  I know the OP said his cat was gone, but for $40 or so the high-flo aftermarket one is a good deal, and really cleans up the stink of the exhaust. 

Obviously, let's get the driveability issues sorted first, though.  Sounding more and more like a weak fuel pump.  Oh- one other thing to check- the WIRING going to the pump.  I recall when I changed the pump on my GMT400 there were some cruddy grounds and weak splices.  Make sure the wiring is all good before firing the fuel pump parts cannon.  And if the filter is more than a year old, replace it.  Might be worth cutting the old filter open to see how much crud it's picked up, too.  And check the fuel pump sock. 

volvoclearinghouse said:

In reply to SkinnyG (Forum Supporter) :

That's a good idea.  IIRC the range is somewhere around 12-15 psi, and I've read that it likes to be in the high end of the range, like 14ish.  Any details on how you modified to add an external adjustable regulator?  I might like to do that on my 454. 

There's not a lot of mods one can do on a TBI system....there's a slightly better exhaust crossover and a high-flow cat will help.  I know the OP said his cat was gone, but for $40 or so the high-flo aftermarket one is a good deal, and really cleans up the stink of the exhaust. 

Obviously, let's get the driveability issues sorted first, though.  Sounding more and more like a weak fuel pump.  Oh- one other thing to check- the WIRING going to the pump.  I recall when I changed the pump on my GMT400 there were some cruddy grounds and weak splices.  Make sure the wiring is all good before firing the fuel pump parts cannon.  And if the filter is more than a year old, replace it.  Might be worth cutting the old filter open to see how much crud it's picked up, too.  And check the fuel pump sock. 

I was thinking fuel filter as well.  Cut that thing open and see if it's junk.  If it is, you may still need a fuel pump.  From my experience, they don't like being run hard AT ALL.

I'm going to say start with the filter. People say that the pumps are prone to failure, and they are, but in my experience 95% of the failures are that they just stop working completely. I can't remember the last time I encountered a "weak" pump on a GM tbi unit. I'm not saying its impossible, but not common. Also see if your parts store has a tool loaner program. They may have a fuel pressure gauge and adaptor for that.

As far as mods are concerned I have read that guys with 5.7 engines gain power by swapping in a 454 tbi unit, but I don't know if that's a simple bolt on or if it's more involved than that.

I had the hose between the pump and the gauge/fuel lines in the tank leak. The engine would bog when the throttle was pressed. 

I don't remember exactly how I defeated the internal regulator.  I kept the rubber diaphragm, but removed the spring, and I think I fabricated a little plate to stop the diaphragm from being forced out the vent holes. I do not believe it was vacuum-referenced.

I added the reg to the return line.

I used a Holley big bore TBI unit on a stock manifold, and had to enlarge the openings in the intake manifold - be delicate and only remove what you think you need to - there is a water jacket real close that you will break into, like if you try to bore it out with stacked hole saws or something ingenious.

You don't really have to defeat the internal regulator unless you want to go both higher AND lower than the factory setpoint. If you want to go lower you can tee off the feed line and into the return line, if you want to go higher you can just put it inline with the return line.  But modifying the stock one to be adjustable might be easy enough anyway. I've done one in my life (not on a tbi, but they're all kinda the same) and it wasn't toooo bad, just real fiddly.

We may be getting somewhere. I got the fuel pressure gauge today and here are the numbers.

key on engine off: slowly climbs to around 9 psi

idling: gets up to around 13 or higher.

wot when its acting up: 7 or 8 maybe 9?

If im thinking correctly it should hold steady in the middle of the range of 9-13 even at wide open. I'll check the ground tomorrow but if it seems ok this all points to a bad fuel pump. That seem correct? If i'm buying a $150 part I really want it to be the right one.

In reply to thundrecougar :

I don't think that rules out filter, but it definitely doesn't rule out pump. Clogged filter can restrict how *much* fuel it can provide at 13psi.

It certainly could be that the pump can't keep up, but try the cheap thing first!

Replace them both, unless the "sock" has collapsed inside the tank or you have another flo restriction somewhere you really shouldn't see that much pressure variation key on engine off, under idle or WOT.  Fuel pump is on it's way out.  The most expensive option on Rock Auto is the ACDelco @ $59, i'd get that one or the Delphi.  Not sure where you are buying one for $150 from. 

thundrecougar said:

We may be getting somewhere. I got the fuel pressure gauge today and here are the numbers.

key on engine off: slowly climbs to around 9 psi

idling: gets up to around 13 or higher.

wot when its acting up: 7 or 8 maybe 9?

If im thinking correctly it should hold steady in the middle of the range of 9-13 even at wide open. I'll check the ground tomorrow but if it seems ok this all points to a bad fuel pump. That seem correct? If i'm buying a $150 part I really want it to be the right one.

Is the pressure regulator referenced to the intake manifold, or just sitting there?

If it's referenced to the intake manifold, the pressure should be constant delta pressure- so 13 psi at idle would be over 20psi at WOT.

If it's referencing nothing, then it should be constant pressure- 13psi all the time.  

But yea, if all else in the fuel system is changed (filter, no other restrictions, and a good regulator) it's the pump.

About that $150 pump, though- is it in the fuel tank?  Can you take it out as a unit and look at the actual pump?  The reason I ask is that I managed to find a replacement pump for my Miata for $15.  It was *just* the pump, and I had to fit it into the assembly myself (inlcuding adapting the connector).

In reply to alfadriver (Forum Supporter) :

They are in tank, and quite cheap if you just want to get it running.  The Airtex brand is 11 bucks, and probably what's in stock at the FLAPS anyway, just not for 11 bucks.

The regulator doesn't seem to have a vacuum reference. The fuel pressure tester I was using replaced the fuel filter with a piece of pipe with a shrader valve on it because there isn't one in the system from the factory, so all testing was done with the filter out of the equation. The pump by itself is cheap enough but the sending unit is bad as well so I need the whole assembly.

In reply to thundrecougar :

Lol, the whole "I'm already there, so I might as well..." 

hope it works this time. 

TBIs don't have vacuum reference because the injectors are above the throttle plate which means they don't experience the changing pressures that port injectors in the manifold do. 

The listed pressures sound like a failing pump to me. 

Something a lot of people don't understand is that if your pump can't move enough fuel for the load, pressure WILL drop.  Normally your pump is moving more fuel than the injectors and the excess is flowing out of the regulator and pressure is regulated to that setpoint and stays steady. Your pump always has to be able to move more fuel than the injectors are moving in order to maintain the pressure setpoint. The regulator only regulates when excess fuel is flowing out of it. 

So basically if your fuel pressure is dropping below the regulator set point your pump or filter is failing.  The slow rise with key on and initial engine start correlates with that as well. 

IIRC I went with the Delphi pump on mine.  But yeah, if you need a sending unit, then I could see the price.

Check all the wiring connections, grounds etc first.  Check voltages at the pump.

Then replace the fuel filter, and check/ clean the in-tank sock.

After all that, if pressures are still low, suspect the pump. 

Yup.  TBI doesn't need referenced regulator since the nozzles are not in the manifold.

10-13 psi is within spec.  The 7-9 you're seeing is an indicator that maybe the pump can make the pressure but not the volume to keep up with higher demand times.

I'm pretty sure I used a pump for a '98 350 Vortec pickup in my TBI application.  The TBI could regulate that pump just fine.

 sounds like what happened to my '89 350. Truck would idle but barely ran under load. New fuel pump fixed it. There is a ground wire for it back there too. Make sure its good. The pump isn't too hard of a job, with the filter off, turn on the key and let the pump drain out the tank so you aren't wrestling with 100lbs of gas.

SkinnyG (Forum Supporter) said:

I'm pretty sure I used a pump for a '98 350 Vortec pickup in my TBI application.  The TBI could regulate that pump just fine.

Both pumps provide about 67 psi.  It's the regulator that makes the TBI work.