I am stumped and have no idea what the problem is. I have an '87 IROC-Z 305 (F) TPI with an automatic transmission. Listed below are the mods.

B & M 2000 Stall Converter, SLP 1 5/8 Stainless Headers, Flowmaster American Thunder Cat-Back, Eastern Manufacturing Hi-Flow Cat, Art Houser Rear End w/ 3:73's Auburn 3 Series Posi & Moser Axels, Upgraded 28 Spline, High Density Custom Drive Shaft, MAF Screens Removed, 160 Hypertech T-Stat, TPI Coolant By-Pass, 8mm Hi-Per Wires, AFPR, Underdrive Pulleys, K & N Air Filters, Manually Wired Fans w/ Switches

For some reason my computer is retarding my timing at WOT and at no other time, except perhaps if it goes into overdrive while going up a hill it may retard 1 degree or so for a second and promptly returns to zero.

I have changed the spark plugs (AC Delco gapped at .035) and checked all the wires. I disconnected the knock sensor once to see if I heard any pinging. Regardless of how high I adjusted the fuel pressure, I still got pinging so I hooked the knock sensor back up because I knew it was working and was not faulty.

I have no error codes on my scan tool. All vacuum lines seem to be fine and the EGR and solenoid seem to be fine (no codes).

Below is how much the computer is retarding the timing at WOT with various degrees of initial timing. The fuel is set at 42 psi while the car is idling. I am running Sunoco Ultra 94 octane.

I would appreciate any hints or suggestions. I can't help but assume this is hurting my 1/4 mile times at the track. Thanks.

0° of timing it retards 0°
4° of timing it retards 5°
6° of timing it retards 5-6°
8° of timing it retards 7-9°
10° of timing it retards 9-11°

 

Sounds like you might want to spend some time here:

https://www.thirdgen.org/techbb2/for...?s=&forumid=16

the PROM burning forum on this site

 

Welcome to thridgen.org.

You basically have a stock 305 TPI w/headers? You shouldn't need to tweak anthing for the "ping" if basetiming is at 6*BTDC (spec), especially running 94 octane.

You could be running a cylinder or two lean, could be carbon deposits, etc. Did you check for vacuum leaks around the injectors too?

I'd check all the plugs, see if any cylinders (or all?) are running lean and go from there.

Also, what's the O2 reading on your scan tool at WOT?

 

The O2 reading at WOT is 840-852. Right now I am running 8 degrees of timing instead of 6.

 

Seems lean, used to be everyone shot for 920-950MV's at WOT, until reading BLM's and WB O2 sensors.

Try more fuel pressure..up it in 2lb increments with basetiming back to 6*BTDC.

See if O2's come up and if it helps any.

 

I put the timing back to 6 degrees and increased the fuel pressure from 42 to 46 with no difference at all. Actually, the O2 reading once hit 860 but was still within 840-852.

Can the knock sensor pick up that "crackling" sound that headers make at WOT? Even so, with the knock sensor disconnected, I was hearing pinging like crazy at WOT, 6 degrees of timing and the fuel pressure starting at 42 all the way up to 48.

 

A faulty knock sensor could cause false knock readings, but you have the problem w/o the KS involved...seems to me the KS is doing it's job.

Funny increasing FP didn't increase the O2mv's...

Have you watched the FP during a WOT run? You'd have to extend the line and tape the gauge to your windshield....could be FP isn't keeping up.

 

That's a good idea Mike. I'll have to check that out. If that's the case, I dread the thought of dropping the tank to replace the pump...

Could a FO relay on it's way out affect the Fuel pump from not keeping up with the demand at WOT?

 

No, shouldn't have anything to do with the relay, you also have a bypass switch that feeds power to the pump...via the oil pressure switch, so even if the relay were "dropping out", you'd more than likely still have power to the pump.

Could also be as simple as the fuel filter, so don't go into the tank just yet...but see what yout WOT FP is, then you can start looking at alternatives...injectors, carbon build up, etc...

BTW, what's the IAC counts at idle?

 

Idle Air Mtr Pos at idle is 30 steps

Is this what you wanted?

I set the TPS sensor at 54 volts with only the ignition on. With the car idling, it always reads 58 volts. When I shut the car off, it goes back down to 54 where it should be.

Also, replaced the fuel filter about 200 miles ago. I think this retard problem has been going on for quite some time.

 

I was just wondering abou a vacuum leak...which would cause the IAC to be lower...seems to be right.

You do get WOT voltage at 4.2 or higher? While depressing the pedal? I/e, just trying to make sure you're actually going in to PE mode...I'd guess so, since you ddin't mention O2's were fluctuating around 450mv at WOT.

Just talking/typing out loud

 

WOT throttle it is at like 4.36 or so. Headed out to check the FP at WOT...Will let you know. Thanks.--Al

 

At idle, the fuel pressure it at 42. At WOT the fuel pressure actually increases to 54 or so. It was hard to tell exactly what the number was because of the gauge being so low on the windshield. I had a hard time seeing it. There definitely was not a loss of pressure at WOT.

 

weak coil?

 

I was thinking that as well but can it cause pinging?

 

I see somehting wrong with the FP setting.

You seem to be adjusting FP without discnnecting the vacuum line to the regulator...that's why it's so high at WOT.

I've read where too much FP can actually ause the injectors to malfunction and "lock up" stuck, due to too much pressure.

Your FP *seems* fine, since you can maintain 50+lbs.

I'd sggest that you disconnect the vacuum line to the regulator and adjust FP to 43/44PSI to start. This will simulate WOT and will be the same (appx) as where the injectors flow is rated.

Do this, then a WOT run and watch the MV's, see where they're at now.

 

Do I disconnect the vacuum line that is attached to the afpr or where it plugs into the plenum? Do I need to plug anything? Do I set the fuel pressure while the car is idling or static? Thanks.

 

Either end, as long as no vacuum is applied to the AFPR..you then need to plug the vacuum line so there isn't a leak into the intake...just for good measure.

Idling would be fine, that way the pump is running...you can set it statically too, but after every adjustment you need to keep cycling the fuel pump to maintain pressure..kind of a pain and if you have any bleed off, not sure how accurate the settingwould be.

 

You know..... a loose engine bracket or an exhaust pipe banging/rattling against something can cause the KS to think it's hearing detonation.

Also....

How to deactivate the KS THE RIGHT WAY to listen for REAL detonation- run the KS wire to a 3900 Ohm resistor and then to a good ground (NOT back to the sensor!). A $0.25 Radio Shack resistor will do just fine. This will make the ECM think it's still got the knock sensor attached, but obviously, it won't ever register detonation. If you just unplug it you'll get a check engine light and the ECM will be running in "limp home" mode- not a valid test. You'll want to reset the ECM to make sure that knock retard is set back to 0 in all cells.

 

Thanks Damon.

I adjusted the fuel pressure as you mentioned and the O2 is now reading 830-856. The fuel is now set at 44 psi the way you mentioned.

What should I do now??

 

When you put the '165 ECM into 8192 ALDL mode (10K across A & B) timing is also added. Seems 8.1 deg is about what most f-body cals use.

RBob.

 

Ahhh...finally someone else joins the party

Now go up to 46PSI (vac line disconnected) and see if you get an increase.

If not, there's several other things to look at...

Injector balance (you'll need a 40-50 dollar tool to cycle the injectors) to make sure none are clogged. You should also read theplugs to verify/confirm/deny one or more cyclinder are actually running lean...and causing your problem.

If plugs look good, injectors look good, you may have carbon and hot spots causing the detonation/ping. Topend cleaner from GM, may cure this.

There's few other things I can think of, but I'm kinda stuck on why you can't get the o2 voltage above 900mv's.

 

Thanks. I will bump up the fuel shortly. I used Gm Top Head Cleaner about a month ago. Very little white smoke after letting it soak for 15 minutes--the engine seemed pretty clean. I hope the O2 voltage increases.

Do you think this could cause pinging? Or are you just wanting to make sure everything is where it should be to start an elimination process? Thanks again.--Al

 

Well, my car setup is a bit different thatn your's...I have 2.77's and a 350, when I swapped my intake and put on my 1-3/4's, I had pinging (kniock sensor is whacked and doesn't pick it up) when I had 40psi in my AFPR, I increased it to 43/44psi, pluged in my scanner...had no more ping and my O2's were in the 920-940range...I didn't scan the car at 40psi.

Anyway, all you've added to the engine is the headers (which would require a richer mixture).

I've had no problem with getting the mv's in the 900-950 range on TBI and TPI engines, that's why I'm wondering if you're runing lean, causing the detonation.

Just by chance, you are running the stock EPROM?..i/e you don't have a Hypertec or other in there, do you?

 

I am running the stock EPROM. I used to run a Hypertech Streetrunner which slowed me down 1.5 tenths and then I used the Thermomaster in which I saw no difference at all in my times. Sold it and now just use the stock chip.

I am really looking forward to the O2 voltage reading once I increase the pressure to 46 psi...

 

Took the fuel up to 50 psi with no change at all in the O2 sensor. Still had a retard problem as well. This doesn't make any sense.

 

Nothing like a good party to attend

Two more items of consideration: the MAF is de-screened. The MAF scalar tables are now out of calibration, to the lean side.

Some O2 sensors just won't go as high as 900mV. Nature of the beast. Best O2 sensor to use is a good 'ole GM AC Delco.

RBob.

 

I'm am going to have to test the injectors. I think that may be the source of the problem. Will let you know what I find out. Thanks for all the help.