What exactly does the est bypass wire bypass? Just the computer advancing and retarding the timing? What all does it stop reading when you disconnect it? This is on a 1991 camaro z28 l98

afaik it just controls the advance on the distributor. Similar to taking the vacuum line off an old vacuum advance dist. The only reason I know to disconnect it is to set base timing.

I was just wondering bc my z will run good until you put it in gear and it will cut off like you turned the key off. If your fast enough to add a touch of gas, it'll stay running. If you disconnect the bypass wire, it'll run all day long in gear at idle. I was trying to narrow down what all the bypass bypasses to know where to look in troubleshooting

Get a timing light and find out what it's at. Disconnected it should be around 6 degrees.

It is. I verified it yesterday

Did you look at the timing with it connected? Does it hold steady or move alot? Could still be a problem with the advance.

Yes. With it connected it starts out advanced past the timing plate. I did notice that at least it holds pretty steady when you hold the throttle in a fixed position

It should advance past the tab. How much it the next issue but without a fully indexed balancer or timing tape it'll be tough to find out if its over advanced.

I think I read a thread about the ecm being able to advance up to 20 degrees past base set right?

There is no mechanical advance in the dist. so I believe it should be able to advance farther than 20 degrees. But I'm assuming that so don't take my word for it.

Sounds like it might be idling too low. When you unhook the bypass it'll idle higher.

Total advance can be about 50° BTDC under some conditions. There are timing tables based upon engine RPM and calculated load (LV8 factor), and then there are adders/modifiers based upon coolant temperature, TPS, MAP, transmission range, a few other items. Idle timing advance can get to near 30° under some conditions. The EST circuitry in you vehicle is part of the MEMCAL in the ECM, unlike older models.

X-X has a good suggestion - Clean the TB and check/set the throttle minimum air position.

Very good suggestion. Ill do it. But actually, it idles low and good with bypass wire disconnected. Hmmm. No codes whih is really cool too. I checked my fuel pressure again and it's 29 psi idling and it snaps to 40 quickly when you snap the throttle. When you first turn the ignition on, it goes to 40, then bleeds down to 30 within a half minute to a minute. I squeezed the fuel return line for a second and it shot up to 65 so I don't think the pump itself is bad. Regulator? It's about a year old. When u disconnect the vacuum from the regulator it rides at 40 and there is no gas coming out no the regulator vacuum line. I'm getting discouraged with this tpi.

Your running pressure is low & it should hold pressure when the engine is off, in fact it should increase slightly.

Ok so I should fix the obvious. The bleeding could be leaking injectors I suppose. Any other thoughts? What do you or vader suggest as to do first?

Prime the system & pinch off the return line, watch the regulator for fuel to dribble out, sometimes it takes awhile.

Ok thank you so much! I'll post the results tomorrow.

Ok I pinched the return line. Nothing came out of the regulator vacuum line. But I noticed today within 20 seconds after prime the pressure is 10 psi. I replaced the fuel filter while I was at it since I had it and of course that didn't help. I don't see any leaks anywhere. No what in the world is up? I'm user the good way more than driving this junk here lately

Ok that bad boy smelled rich too. Do I have an injector stuck open? Maybe the regulator just can't keep up. What say ye?

Prime it & pinch off both pressure & return lines, if it still bleeds down then its most likely an injector.
If it doesn't bleed down the there might be a leak inside the fuel tank or a bad one way valve in the fuel pump.

Thanks! You guys are awesome! I'll try that ASAP! I'm away from the house right now, but I'll be sure to post hopefully tomorrow! Thanks again!

That reminds me. Several times when I got to a quarter tank of gas the pump sounded like a cat was in the tank for a few seconds and it died. Filling it up and realizing it had 4 gallons left made me scratch my head. Since then I've kept half a tank or more in it. I hope it's the pump. If it is I'm replacing sending unit pump strainer hoses and all. Is that a check valve in front of the tank? (That plastic thing)

Why does everyone call this the EST? It is Electronic Spark Control, yes?

GM calls it Electronic Spark Timing.

That explains a lot!

Ok it still leaks down maybe a tad slower if you exaggerate. When I finally let go of the lines it plummeted to 0 psi.

So I'm guessing I need a set of injectors from South Bay? Mine are only a year old but they are accel 24lb ones which I hear aren't the greatest. I wouldn't mind swapping them for a set of 22lb Bosch.

I'm confused by this. Maybe I'm reading it wrong. What do you mean exaggerate? So if you pinch off both lines it holds somewhat steady? When it plummets, what line did you let go of? If its the pressure side then its likely the hose/pulsator connecting the pump to the sending unit is leaking fuel back. If it's the return line then likely its your regulator. If it leaks while both are pinched then its your injectors.

Yes it leaks while both are pinched. I was a bit unclear. I meant that when you pinch both lines, it really didn't slow down much if any.

I let go of both at the same time instead of one at a time and it dropped to 0. I'll try lettin go of one at a time and see as well.

Ok. I just checked again. I must have not had a good bite on the hose yesterday but I checked this morning and the pressure in fact holds pretty steady with both lines pinched. I let go of the pressure and it immediately fell to 0. So it looks like I'm heading into the tank! It might be a week or so before I get time, but I'll definitely post any updates!

One quick question, should I use a delphi or ac pump? I'm changing the sending unit as well. Is a spectra sending unit fine to go with?

Some people on here say to replace the pulsator with a piece of hose. Is tht te best thing to do?

Either pump choice is fine. It's a horse a piece either way. I had a year old delphi unit go before and delco parts as well. As long as you stay away from most 'house' brands at parts stores you'll be ok. Your original sending unit should be just fine. Unless its rusting out. I've only had a few spectra parts and they seemed ok but, they weren't as sophisticated as a sending unit.

As far as the pulsator....
https://www.thirdgen.org/forums/tpi/679381-faulty-pulsator-replacing-pump.html

Wow I'm gettin a new pulsator. That would drive me nuts!

If I ever have to pull my tank out again, I'll switch back to a pulsator. I have a tick that sounds like a loose rocker arm. And thats with two different engines.

Ouch. I just ordered an ac pulsator to solve that potential problem

Ok I just replaced the fuel pump, sending unit and hoses. The good news is the fuel pressure does not bleed down when it's primed. The bad news is it's still only priming to 40 psi and running at 30 psi. I'm assuming I may need another fuel pressure regulator.

The car still stalls at idle as well. I will pull a few spark plugs and see the condition of them and clean the throttle body an iac while I'm at it. Any other suggestions?

Ps just had check engine light come on tonight code 32 and 42

Ok 42 makes sense bc I verified my timing tonight

I do notice in parking lots with light throttle I hear some solenoid sound like a rapid open and close loudly. My first guess was the erg solenoid.

I'm not sure what clicking you'd be able to hear. The egr solenoid is pretty quiet. It could be bad giving you a code though. Sounds like the bad idle is your egr valve hanging open. I'd test the solenoid first then pull the plenum to see how crudded the egr passages are.

Sounds like a plan. That sucks bc that egr is a year old and the engine was remarkably clean when I changed the lower and upper intake gaskets. I'll definitely look into it though. I'll keep y'all informed.

Ok what I wanted to point out is that it will idle correctly and not stall with the est bypass wire disconnected. That would rule out an egr problem of that magnitude wouldn't it?

If the egr was off recently and it was clean underneath then the solenoid is much more likely. The solenoid might not be venting properly and causing the egr to hold open. You can always use a vacuum pump to test the egr valve with the manifold still in one piece. And just because the est was disconnected and it runs alright doesn't rule out egr problems. Your changing the timing drastically. http://sethirdgen.org/egr.htm

Thanks! I hope to test it tomorrow or Monday! I'll update!

Sorry it took so long I finally got out there this morning. I cleaned the throttle body and put a delphi iac on, changed the egr solenoid with one from a 95 deville (new) and just because they're old changed the air pump check valves. No change. Good thing is I still have to check the egr diaphragm. That's where I'm at. Grrrrr...

Question ?
Did you follow these directions for setting the IACV
= https://www.thirdgen.org/tpimod2
A digital timing gun with RPM display is what I finally broke down and bought.
Makes a standard gun look like a toy.

This is the one I picked out and the price here is close to half of what they want at the Auto Parts store.
= http://www.toolfetch.com/innova-3568...FYY7MgodZGcAaQ

Ok I sent the car to a reputable shop that still has a obd1 computer scanner that the dealerships used to use. They found a problem with one of the leads to the coil, and most importantly the brand new ac delco ignition control module was faulty! They bought another ac module and it purrs like a kitten in gear. Sigh.........

Good to hear it's running well. A scan tool in hand is worth...two in the bush? Wait. Thats not right. Anyway. Did that solve your code 32 as well?

Not sure yet. I haven't driven it much more than from the shop. It started rain