'82 Cross-fire running open loop

[wishuwerehere82]

'82 Cross-fire running open loop

I went to the Chevy dealer to get a new ignition module in a last-ditch attempt to fix a problem that I seem to continue to have. He said they were discontinued, but pointed me to Meizensahl's auto parts that had them in stock. While talking to Charlie at the parts desk, I told him of my problems and he offered to put a diagnostic scanner on my '82 after work on his own time.
He advised me not to put in the new module until we had a chance to check it out first.
We met at a diner parking lot and he plugged it in and guess what? There are no codes stored! Nothing!:confused

We put it in active mode and monitored the ECM and it is running open loop for most of the time. It went into closed loop once and smoothed right out, but a few seconds later it went back into open loop again and stayed there.

The readings we were getting were:
Prom # 9531
Temp= 195 degrees.
O2 went from .53V in closed loop to 0 Volts when in open loop.
O2 cross count=none 00V
IAC motors went from .17V in closed loop to .007V in open loop.
Map sensor= 10" HG at 1.44V in open loop.
Knock sensor= 0V in open loop.
TPS sensor= .56V in open loop.
Timing= 9.5 degrees in open loop.
The mixture alternated between rich and lean while we were monitoring it in open loop and most of the usual stumbling and oscillations were observed.

Needless to say, this was a real eye opening experience.
To sum it up, all of the active feedback and control outputs to the fuel/air management system are off or at least at default values.
It seems to me that I have an intermittant open circuit on my O2 sensor somewhere or a bad new O2 sensor.
Or does a 0 Volt reading on the O2 sense mean a short to ground?
Or a bad connection inside the ECM somewhere. Maybe the active memory is fried in the ECM?
Any ideas? My brain hurts!

Pete.

 

[brusso]

'82 Cross-fire running open loop

It seems to me that I have an intermittant open circuit on my O2 sensor somewhere or a bad new O2 sensor.
Or does a 0 Volt reading on the O2 sense mean a short to ground?
Or a bad connection inside the ECM somewhere. Maybe the active memory is fried in the ECM?
Any ideas? My brain hurts!

Pete.

Yes. The O2 sensor produces a voltage, when hot, to indicate a rich or lean condition. So if you're reading 0 volts, it could be any of the above.

 

[wishuwerehere82]

I pulled the ECM out and tore it apart this morning, cleaned up all of the card edge connectors on the two boards.

I verified that the O2 sensor was making contact with the ECM connector without any opens or shorts.
Put it all back together, and took it for a warm-up run.
It definitely ran better and did not have the surging, but is still not 100%. It still misses at idle a little and shakes a bit.
I wish I had one of those diagnostic analysers to see what it is doing now.

Pete.

 

[Pancho]

Sounds to me like you might still have a little vacuum leak.....

The low O2 voltage indicates a lean condition, but going open-loop at idle is normal since there's not enough exhaust flow to keep the sensor heated up.
The O2 should really only be 'believed' when it's warmed up and probably that takes > 1000 RPM or so. Most testing is specifed at 2000 RPM or so.

The IAC (Idle Air Control) is controlling the air bypassing the throttle plates at idle; a low number would either indicate the system's trying to 'pinch off' the idle air passage. It would be helpful to know what the IAC counts are doing when the engine is idling unstable.

I'd try either spraying carb cleaner or passing a propane torch (un-lit !!) around the base of the throttle bodies, intake manifold, vac hoses, etc. If the idle smoothes out you found it. (For that matter, to see if it's a lean-misfire at idle, pass the propane over the air intakes of the throttle bodies to see if it smoothes out).

Another item; in your earlier post (pre-manifold gasket replacement) you said you had 10"Hg of vacuum...... with the scan tool you read 10"Hg of MAP. MAP is 'abolute' pressure (relative to perfect vacuum), so 10"Hg of MAP is roughly 20"Hg of vacuum assuming you're near sea level. (~ 30"Hg barometric - 10"MAP = 20" VAC). Just wanted to clarify that since when I first read the latest readings I thought you might still have only 10" of vacuum....

Hope some of this helps,
/Pancho

 

[wishuwerehere82]

Pancho,

How's it going?
Yesterday was a bummer for me as I put a new O2 sensor on and everything seemed to rum worse than before, after I pulled the ECM and had it running pretty good.

The IAC's, according to the scanner, were not doing anything since they had.007 Volts and didn't change.
Thanks for clearing it up about MAP. I was running about 17" HG on the rear TB but it was not stable 14-18".

I think maybe my ECM is toast. What do you think?

Pete.

 

[Pancho]

I'd check for other stuff before blaming the ECU;

Did this surging just start all of a sudden, or has it happened gradually? Did it start after some other work was done?

Does it 'always' run good when in closed loop, and 'always' bad when it's in open loop?

Do you remember seeing some parameters called INT or INTEGRATOR and BLM or BLOCK LEARN on the scan tool? Do you remember what they were reading?

 

[wishuwerehere82]

It has been doing it for a year or so, but has not geen right since I rebuilt the engine 3 years ago.

I didn't get any codes out of the ECM which is strange. There should have been 50 stored codes in the memory, since until yesterday I had not disconnected power to the ECM.

I don't remember seeing any other values on the test scanner other than MAP,O2,O2 CROSS COUNT, IAC,TPS, RPM, TEMP AND KNOCK.

If there was any we might not have done the right test for the memory.

 

[wishuwerehere82]

I'd check for other stuff before blaming the ECU;

Did this surging just start all of a sudden, or has it happened gradually? Did it start after some other work was done?
It has always been doing it, even after replacement was done on all sensors.
Does it 'always' run good when in closed loop, and 'always' bad when it's in open loop? Seems to.
It runs good after RPM is high and I back off the throttle.
It kicks all cylinders on and stays there until I go back to idle. If It doesn't kick, I hear a cylinder ticking, not a lifter sound, more like the gas is detonating in the exhaust manifold, and it seems to run on 7 cylinders.
Do you remember seeing some parameters called INT or INTEGRATOR and BLM or BLOCK LEARN on the scan tool? Do you remember what they were reading?

Didn't see any of the parameters.

 

[Pancho]

I don't thing the early 80's ECUs had memory codes like the OBD-II systems since '96; the only time you get codes in the older systems is when the check engine light is on.

You might also want to do some google searches on cross-fire injection system, to see what others have found.

Good luck,
Pancho

 

[wishuwerehere82]

This is the only helpful one that I have found so far.

http://www.crossfire.webhop.net/twinnie

Thanks for all the help.

Pete.

 

[wishuwerehere82]

I ran a compression test on the engine and am changing the plugs and wires now. Here's the scoop!

#1 145 psi
#2 150
#3 150
#4 150
#5 155
#6 150
#7 155
#8 145
When I started Idid the #2 and 4 cylinders first.They pumped up about 70 psi on the first cycle then came up close to 150 on the second one. Once I had oil pressure in the rings all the rest jumped up to close to 150 on the first cycle. I guess rings and valves are eliminated.

Pete.

 

[wishuwerehere82]

Oh yeah, now I remember how much fun it is to change plug wires the "right" way. It only took 6 Hrs. And I only had to drop the starter. By the way, it doesn't run any different.

What's left? Cam, Lifters, valve springs, head gaskets.
It's probably easier if I just pull the engine to do it.

Pete.

 

[wishuwerehere82]

I spent some time today going over all of the calibrations on the fuel injection and I found good news. The balance on the TBI's was really off! The rear one at 7" of water was balanced with the front one at 10" of HG. I don't know how it slipped so much, but after balancing again all cylinders ran pretty well, and it seemed to be in closed loop mode.

The big difference was that this time I left the IAC's plugged in and ran it dynamically without plugging the IAC ports. There's only about 10 degrees of "sweet spot" on the adjustment screw. Turn it to either side and it goes open loop. So once I established idle at 650 RPM, instead of using the throttle stop screw to adjust the engine speed, I made some shims of paper strips and put them in between the throttle stop screw and the throttle lever and removed strips until the rear TB was reading 7" of water.
I think that the bushings on the rear throttle body is shot. It has a lot of up and down play in it and could be why the balance won't stay put. I have a spare set that I will have to send out to Turbo City be rebuilt while I limp along for now.
I may need to re-adjust my lifter backlash to see if that helps too.
All in all, it was a good day!

Pete.

 

[wishuwerehere82]

I adjusted my lifters yesterday using a vacuum gauge. my parts guy said it was an old racing trick. I backed the valve nut off until I heard the rocker arm click, the tightened it a half turn and kept going until the vacuum was the highest then stopped. I did all the valves like that, twice to be sure. When I was finished, the intake vacuum was up from 17" to 21" on the gauge.

I still have a cylinder that sounds like it is loping, but the driveability has gone way up. It doesn't surge anymore, and the throttle is not as sensitive.
Pete.

 

[curtis]

I don't know squat about your fuel injection. Just curious about the valve adjustment procedure you used. You must have hydraulic lifters. After the clicking goes away and you go 1/2 turn more, that centers the pintle in the lifter giving it the correct preload. If you go farther ,doesn't that remove all the built in cushion sort of speak and basically turn it into a solid lifter? Wouldn't that put undue pressure on things and create high cam lobe and lifter wear? Sounds scary to me. Can you enlighten me here?

Is it the engine temperature that determines whether engine runs in open or closed looP? If it is , maybe you have a problem with the temperature sender or wiring. Like I said, I don't kinder to this electronic stuff, but if you ground the lead from the temperature sender does the engine go into closed loop?

 

[wishuwerehere82]

I don't know squat about your fuel injection. Just curious about the valve adjustment procedure you used. You must have hydraulic lifters. After the clicking goes away and you go 1/2 turn more, that centers the pintle in the lifter giving it the correct preload. If you go farther ,doesn't that remove all the built in cushion sort of speak and basically turn it into a solid lifter? Wouldn't that put undue pressure on things and create high cam lobe and lifter wear? Sounds scary to me. Can you enlighten me here?

I didn't go any further than 3/4 turn in, which I believe is still in the normal preload range. According to my parts guy, the 1/2 turn variance on the lifters is a general spec but can be optimised using the vacuum technique.
I certainly don't want to excessively preload the lifters, however I will say I got a lot of improvement on the intake vacuum using this technique.

Is it the engine temperature that determines whether engine runs in open or closed looP? If it is , maybe you have a problem with the temperature sender or wiring. Like I said, I don't kinder to this electronic stuff, but if you ground the lead from the temperature sender does the engine go into closed loop?

I think it is a combination of Temp , MAP and O2 readings that closes the loop. Once the engine comes up to temp, it monitors O2 and when the MAP is high it goes into "Enleanment" mode until the O2 sensor reads low, then it goes into "Enrichment" mode and keeps going back and forth trying to optimise the fuel/air mixture several times a second based on the O2 reading.

Pete.

 

[curtis]

darn electronic confusion modules. Sorry I couldn't help. Somebody should be able to figure it out for you.

 

[wishuwerehere82]

Thanks Curtis,

I wish that were true, but I have been talking to myself for a week now and it doesn't seem to help.:L I clamped off all the vacuum hoses that come off the intake manifold and the vacuum still keeps going up and down about 3". If I do the math, 21"/8 cylinders is 2.625 "per cylinder which tells me that 1 cylinder is intermittently firing and causing the loss of vacuum until it turns back on again. That is, if I do the math, and math has never been my forte. I guess it could be the IAC motors cycling and letting more air in, but I just don't know.
Darn Comfuser modules, I miss old engines.

Pete.

 

[curtis]

I know too little about this engine. How about distributor cap or sticking EGR valve. my last resorts.

 

[wishuwerehere82]

I checked 'em both.

Today I ripped the throttle bodies off and checked them out and rebalanced them. No difference with new gaskets.
I'm going to put a new fuel filter on tomorrow and see if that does any good.
Thanks for the reply, Curtis.

Pete.