xzvs

It woke the car up a bit but it still feels like over 3200 it just hits a flat spot and barely pulls. Acts like a clogged air filter or fuel filter (or like ignition is retarding). EVERYTHING is new tune wise and the fuel pressure is at 47 psi while the problem is occuring. Its got a new timing chain and gear set too. Cats are recent, but I got the car with a blown head gasket (happened after the new cats) It had been super dependable , but has had this prob since I put it together. I put it on a snap on scanner and all reads honkey dorey sensor wise. Have tried premium fuel too. When I free rev it, it tries to stall out and runs rough for about 10 secs after. Any ideas? I'm stumped

Rich B.

Several things come to mind here...

I'd say the prime suspect here is the catcon. Have to disconnect it to check, but that's how a clogged catcon behaves. Then, -

1. Do you have the latest ESC module? Not the module in the dist, but the 4-prong square module over by the a/c condenser housing. Not a *good* one, but a *new* one. GM updates them periodically.

2. Do you have the latest MemCal for your car? Not a good one, but a *new* one, with the latest BIN from GM in it. GM ...yes, you guessed it, GM updates the BIN periodically. And they change things like injector pulse width and spark advance throughout the RPM range.

How about timing? Set to factory specs, and correctly?

More peeps will chime in here eventually with other suspect problem areas...

But my car had problems like you describe; after replacing these (yes, and more) parts, I have a car that pulls admirably...But this is where I'd start.


[Modified by Rich B., 6:44 PM 8/25/2002]

xzvs

ok-- lessie --the timing is set to 8 deg -6 is factory, but I tried it at 6 and 10 and decided on 8. The cat cons were changed 5 mos before the head gasket blew (all 3 --I checked ) and it passed smog with flying colors. I guess if I ever get the money I can have em checked again tho. I did notice that sometimes on accelereation that the a/c quit blowing out the panel vents. Seems I remeber if the cats are plugged vacuum being high in that case? What is an esc module?? never heard of it. There is a small square module by the evaporator case--is that it?? Whats it do? I assume the mem cal is the interchangable chip on the ecm. I think thats stock --would a hyper chip or the likes help? This is my training wheels vette --and I will be moving up to a lt-1 or a zr-1 as soon as finances permit. This will be never if I keep throwing parts at it and not fixing the prob tho :(


[Modified by xzvs, 5:05 PM 8/25/2002]

Rich B.

Then maybe you're getting knock counts and the ECM is retarding the spark...

How about idle? A clogged catcon will start up OK, but the idle will slowly go down until it stalls...

ESC is Electronic Spark Control module; yep, that should be it. There's a good thread on what it does in the Archives; look for a thread entitled "Kudos to the man" (It's a Gordon Killebrew tip; I think from last year's Carlisle show).

The Memory Calibration Module (MemCal) is the snap-in module holding the EEPROM chip that the BINary code is contained in. GM updates/updated them periodically (the binary code).

A custom chip (not an aftermarket rip-off) will definately fine tune your setup, but as you said, until you find out what's causing your bog at mid to high RPM, it won't do you any good.

xzvs

Nope --discoed the knock sensor and it does the same thing. In fact, I thought it was the knock sensor and thats why I played with different timing settings --runs best at 8. Idles fine --runs great on the highway --its just past 3/4 throttle I have the prob. Yup --checked the tps --reads fine. previous owner says it ran great at wot before --so I don't think it a calibration prob either. BTW thanks for your replies --I appreciate it .. Maybe one day we will lick this thing :) I will look into the esc and see if any info is helpfull. I was a drivability guy for chrysler for 15 years --so this is really bugging me that a chevy is getting the better of me.

xzvs

update --tonight it died on acceleration on me --bout 1/2 throttle when it shifted i didn't lift and it just flat stalled out completely. When I cranked it , it spun like it had no compression in like 5 out of 8 cyls. Let up off the key for 3 secs --it roared back to life and ran strong --what the heck is going on here ?

NUckINg FuTS

Did you check fuel pressure at full throttle???

xzvs

was 46-47 psi while doing it with the gauge on it (just the power loss bit --never stalled with the gauge on) --note --i didn't have the gauge on tonight. It does the stall thing bout once a month. won't start till i come to a stop and wait 10-20 seconds.

xzvs

Explained this last thing to our engine guy --he said --oh that's easy --you need lifters. You had coolant in the oil --problem didn't exist accoriding to the prev owner- its happening at high rpms --and when it stalls it takes bout 10 seconds for the lifters to bleed back down. Sounds likely to me but hey I'll wee on a spark plug to nail this prob. The crane oe rollers have check ***** to prevent "pump up" which is what my guy is saying is the problem. They are $169 at summit. My question is this now, I think I should re-adjust my valves and see if it changes. My guy says --nope wont change a thing -its a mechanical problem and that wont help. So, whilst still deciding what to do--I need a memory refresher. The L-98 has to have the intake off to change the lifters?

Rich B.

That would be correct...It's easiest that way... :crazy:

Mo_Bandy

I had a MAF sensor go bad without kicking codes... Try unplugging it and see if the car smoothens out... I had this on both my 87 and 89... It would periodically runn great then other times totally run like ... well horse feces LOL... it might be worth the try before totally digging into the engine.

Just a thought...

Mo

bill mcdonald

Can getting some oil water mix in the lifters really screw em up, even if it is for a little bit?

gcrouse

Check your fuel injectors too; 14-16 ohms.

And yes you have to pull the whole top end off to get at the lifters.

xzvs

checked em all months ago 16 ohms on the money all of em. all the cars that I have done head gaskets on I have changed the lifters. I didn't want to put a whole lot in parts in this thing off the bat --cause I didnt even know if the bottom end was good. Not only did the car have water in the oil but it sat 2 years like that. So, whats the consensus? You guys think this'll fix it or am I after more wild geese? Car is a joy to drive and has great power sept for the having to let up at about 3500 thing.

xzvs

Ran some bg engine flush and their MOA . Made a world of difference. It still there but not nearly as bad. I musta had some crud in the lifters --will drive it all this week and see if it improves and will probably re-adjust the valves to 1/4 turn next sat. Wheres that turbo ricer now -GRRRRRRR

NanoBrain

First off, I would use the Scan tool again, but try to capture data at the moment of “loss of power”. Look for BLM and Integrator values, should be around 128. Look at 02 mV’s and crossover counts, and timing advance/retard, carefully watch TPS voltage signal, watch injector pulse width, system DC Voltage.

Well here's my list of things to check:
MAF Sensor- while idling at operating temp, hit the MAF with your knuckles, if it affects it, change it out! MAF’s are known to cause problems even without throwing Codes. If you can temporally swap it out, it might be well worth your time!!!

Fuel delivery- Fuel filter, Fuel pump, Pressure Reg, what’s the PSI at WOT?

TPS- They can read OK at idle, but have drop-outs through out it potentiometer travel.

12VDC power- Are the Positive and Ground cables good, good connections to battery, loose ground somewhere? Does it maintain +/-13VDC at WOT, it’s good to check with a Scan-Tool, opposed to at the Battery with a DMM?

EGR valve- Could be getting bad.

Sorry, did you say the Cat's were changed out before or after the Blown
Gasket(s)? If before, they could easily be plug up again!

O2 sensor- It could be defective/out of cal., it's probably original.

ECM- Sometimes they throw no codes, or funky codes when defective. This can cause all kinds of strange drivability issues. $79 @ Autozone!

You could bring it down to a local shop, and tell them you want to do “Off-Line” sniffer test- I.E. don't transmit results to DMV. This will point you to Lean/Rich conditions.

BTW does it do it when cold (open loop mode) or hot (closed loop mode)?
Good luck- sometimes EFI can be a PAIN IN THE butt to diagnose!

:crazy:NanoBrain:crazy: