The ecm is retarding the timing 10 deg. due to knock sensor reading...

I have hypereutectic pistons and if there was detonation going on, I think they would have shattered by now.

Car runs great, has run the same for tha past several years. I just hooked it up to a MAC Tools diagnostic computer machine thingy to check the accuracy of the stock temp guage when I came accross this timing issue.

[FYI: the stock temp guage in my 87 is WAAAY off!!! Car is actually running hotter than what the guage is reading...very scary!]

There are no codes, car runs great (except for the cooling and brake issues that most of us have or have had).

My buddy with the diagnostic computer thingy says the knock sensor could be picking up noise from the roller rockers, headers, noisy injectors, etc...which I've read elsewhere before.

So...

#1...would the ecm be retarding the timing that much for ANY or ALL of those? 10 deg. seems like an awful lot to me.

#2...is there anything else that would cause this, other than detonation?

#3...how much power am I really being robbed of with 10 deg. of retard?

#4...could this be contributing to my cooling issues (or lack of, I should say)?

Any and all help is greatly appreciated.

Troy

 

Do you know that the coolant temp read by the ECM is correct?? Could be an issue with the sensor in the front of the intake base, near the cold start module.

If you clear codes just before checking with the scanner, does the timing retrad come at idle or only after driving on the street??

You can test the knock senfor circuti (knock sensor + ESC module) by rapping on the engine near the sensor and looking for knock retard on the scanner.

 

I don't know for certain that the CTS is correct...I just assumed, it's like 5 or so years old. Wouldn't that set a code as a faulty CTS? I'll have to check into that...off to the store tomorrow for a mech. guage. The ecm says the car was @ 225* when the stock guage was reading on the line between 100* & 220*. If the CTS is accurate, I'd hate to see what the ecm says when my stock guage is reading 220 or higher. But you'd think I'd see or hear the coolant boiling over...hmmmm....

There were no codes to clear to begin with and the scanner didn't pick up any new ones. Like I said before, the car runs great. No performance issues to speak of.
I drove the car into the garage after a half hour drive. Only turned the car off long enough to hook the scanner to the battery and ALDL.

At idle, it's retarding anywhere from 0-3* and when given throttle (took it up to around 3000rpm) it's retarding anywhere from 6-10*. It constantly fluctuates. Doesn't stay on one value for long.

I feel almost certain IF the reatrding was due to actual "spark knock" (i.e. detonation), I'd be experiencing noticeable performance issues by now, if not complete catastrophic failure, right?

 

Though the CTS and guage sensors are located in different positions, that sounds like quite a difference and one of concern when the gauge gets to 225. It would be interesting to see what the ECM is seeing when the gauge is up there??

Since you are getting no codes, the knock sensor is ok and the ESC is passing knock signals. Still the ESC could could be sending false knock counts. I replaced replaced the stock ESC in my '88 Vette with the recommended "upgrade" unit and it cured my false knock issues but I'm not sure if the same ESC is used in the F-body cars.

Could there be some metal-to-metal contact that gives falase knock?

Do the other ECM readings look ok, e.g. is it in closed loop at idle and staying there when you rev up and hold say 3k RPM?

How is the A/F ratio at idle and when reved?

When I had the false knock issue with the Vette I could only see a performance hit in trap speed, otherwise it ran fine and "felt" strong.

In what area of the country do you live?

 

the only metal-to-metal probability would be the roller rockers tapping the valve covers...this would not surprise me. Those guys are crammed in there!

I'm not sure of the other ecm values...I'm not at all familiar with what "normal" is. Although I do recall it saying the A/F ratio was lean @ idle,...don't remember the value though. I didn't even think to check it when I rev'ed it.

With the temps being as high as they were, I'd assume the car was running in closed loop. I don't remember seeing that on the scanner though. But again, wouldn't I have noticed some sort of performance issue if it were popping in-and-out of closed loop?

I'm located in central PA...Altoona.

I've had this car for 11 or so years now. Been through most of the common TPI issues. But this is the first time I've had it hooked up to one of these MAC scanners. For all I know, it's been retarding my timing since I rebuilt the motor 7(ish) years ago. I haven't had it to the track in about 3 yrs. So I can't say for sure if there has ACTUALLY been no change in performance. But it runs like it always has, pretty much.

My esc has 2 female connectors, side by side. One is a 2 or 3 wire, and the other is like a 5 or 6 wire. One goes to the tach, the other to the coil. They stick out of the back of the dist. My dist is the skinny HEI type. The one that does NOT have the coil in the cap. The coil is bolted to the rear pass. side of the intake.

Don't know what the 'vettes had in them....Sound the same?

I'll check the fuel pressure tomorrow to see if that is the "lean condition".
If my oxygen sensor was the culprit, that would send a code, right?

What am I looking for as an A/F reading?

And then hopefully my buddy isn't too backed up and can get me back in so I can get some concrete ecm values, so I don't sound like a complete idiot...LOL.

Thanks for your help thus far tho...keep it comin'!

 

If you actually are running very hot the ECM is likely saving your engine by pulling timing so you don't hear ping.

Your dist is like the one in my "new" '88 IROC; both the '88 Vette and my old '86 IROC had the coil-in-cap style. Soon as I finish the heater core R&R I'll take a look at the ESC setup.

If the ECM is dropping out of closed loop for some reason I would think it would set a code but not sure.

I'm located in SE NY near the Hudson and not sure how close is Altona, PA. If you were close I was going to offer to hook up my AutoXray scanner to see if anything looked "unusual".

 

I'm like right in the middle PA. It's about a 4hr drive to the north eastern corner of PA from here. I do appreciate the offer very much, though.

Hopefully the Mac scanner will yeild me some helpful info. I'm hoping to get in there tomorrow, but that depends on Scotts schedule.

Do you think the the ecm IS, in fact, picking up "ping" because of the high temp and retarding the timing accordingly? Would that show up as "knock" on the scanner?...hmmm....that would make sense because the "ping" wouldn't really be audible (due to the exhaust, RR's, injectors....etc) but the ecm would detect it. And when it heats up like that, I certainly don't "hot rod" around, so I definitely wouldn't notice any change in performance.

Now my mind is starting to ease a little. All of that definitely makes sense to me. Any of that make sense to you?

Does the Auto Xray do anything that the Mac scanner doesn't? Another friend of mine has one. He's only like 100mi. from me.
I have NO experience with either one so if you think the Auto X is the way to go, I'll give him a call. Otherwise I'll see what I can get from the Mac Tools thingy.

 

Well at this point I think a little more info is needed, like:
-what is the coolant temp seen by the ECM when timimg is pulled
-what are the knock counts and when do they occur
-what does the O2 sensor data look like
-what does the BLM cell & Integrator (fuel enrichment) data look like
-is the ECM staying closed loop

The AutoXray is a hand held unit that can be set to simply give a single scan or monitor ECM data over 15sec. I've used mine to monitor O2 sensor data during a WOT burst off idle to set fuel pressure.

My AX is maybe 8yrs old so I have to manually copy data; the newer units have a PC interface for easy upload of Monitor data.

The unit comes with a manual that explains briefly the data readings but more information about the sensors and trouble shooting can be had from "Chevy TPI Fuel Injectorn Swapper's Guide" by John Baechtel.

On a recent trip to NE OH I had to buy a new copy to diagnose some codes on my "new" '88 IROC; if don't have the GM Shop Manual for your IROC and would like my old copy of Baechtel's book I'll be glad to mail it to you.

 

Well, I couldn't get into my buddys shop today. And I won't be able to until next friday at the soonest. I'll be out of town from sundaY to thursday.

So further diagnosis will probably have to wait until then.
I wrote down those things you listed in the above post so when I do get in there, I know of at least a few things to look at.

What is an optimal reading for...say the o2 sensor?
What is a good A/F ratio?

I f you are willing to pass that book along, that would be GREAT!

ADDY:
Troy Wilt
2504 Oak Ave.
Altoona, PA 16601

GREATLY APPRECIATED!

I did check my base timing, TPS, and Fuel Presssure today.

Timing...: 6 deg. Adv.
TPS......: .585 closed & 4.20 wot. I was told that it should be .540-.560 closed & anything over 4 wot.
I doubt that would account for much but I went ahead and adjusted it to .550/4.10

Fuel pres: was @ 50lbs. w/ vac. unhooked. I went ahead and bumped it up to 54(that's what I used to run at the track).

Those are really the only things that I know how to check/adjust.

 

I just jotted your address and will try to get the book out to you early next week.

You really need to test the TPS lower voltage with the IAC pintel fully extended and at base idle position of 450rpm.

You might try to borrow your buddie's AutoXray for a week or so. It often takes me some data gathering, some thinking about it and then some more data taking before I resolve some issues.

I just got the new heater core back into my IROC last night and tonight the cover went on and some dash components got installed. Tomorrow I have a Corvette Challenge event at Raceway Park in NJ (hope to go some rounds as I've slipped to 2nd place in the standings). Sun. I'll try and get the IROC buttoned up, do the TB coolant bypass mod and maybe get the lighted mirror and Cobra wiring installed.

I love owning two "old Chevys", always something to do...lol

Have a good weekend.

 

OK, I'm back. I got my high temp issue solved...clogged (internally!) radiator! New one = COOOOOL!

Gonna try to get to scann some things today.

About the TPS...In noooo way can I get my idle down to 450rpm...I think it's either the cam or the TPIS chip that won't let me get it down that low it'll just stall on me. I can get it down to about 650 or so, but the idle is too "lumpy" for me, plus it'll stall occasionally...then again, this is according to the factory tach....I'll check the idle on the scanner when I get there.

Something else to note, When I adjusted my fuel pressure the other day, after I shut the car off, the fuel pressure dropped off rather quickly (in about 10-20 seconds) until it hit zero. Could this be a failing fuel pump? If it were leaking injectors , I would expect to see a plume of black smoke when I started it up afer a few minutes? The injectors are the stock 22 Bosch's. After 20 yrs, I guess they very well might be leaking....

 

Good to hear you solved the coolant temp issue. I just changed the lower radiator hose after installing a new heater core; what a pita, had to remove the booster fan assy to access the hose clamp bolts.

Since you can only idle down to 650rpm you should be able to get by with a TPS low end setting of say .70-.75 Vdc; if you get it a little too high the ECM will throw a low TPS code and you can just back off a tad. The closer to the limit the snappier the response at the off-idle hit of the throttle.

That 10-20 sec leak down rate sure indicates a leak somewhere in the fuel system. Fast FP leak down can be due to 1) leaky injectors, 2) leaky FPR, 3) leaky fuel pump check valve.

The usual symptom of leaky injectors is hard warm starting, even w/o a plume of smoke. To test for lealy FPR or check valve you need to access the rubber fuel lines near the fuel pump so as to clamp them while watching fuel pressure.

If you want the injectors serviced I strongly suggest Rich at Cruzinperformance (link on my site). He cleans, leak tests and clow tests the set for around $100 + shipping each way; in shop time is 48hrs. I've had him do the injectors in both my IROCs as well as in the Vette and have been totally satisfied.