Howdy all,
I've been dealing with an occasional misfires (or at least think so) of my Vortec. Things fixed so far: replaced distributor cap, plug wires. I've ordered a new distributor set and a coil (they're under way). That issue really keeps me awake.

Today I have replaced the wires (I would have some "friendly" words to the designer for a wire's harness underneath brake booster).

As soon as I had it done, I wanted to observe what is going on: I've switched AT to park and start the engine. Starts lovely, from a 1st kick, on idle I had a steady 500rpms (or about). Just felt a tiny shakes (from an occasional misfires?). O2 readings were normal. Engine running in a closed loop. I've set the throttle to get about 3000..3500 rpms. The engine speed up roughly. Noticed, that 2nd bank O2 sensor readingwent down to zero. A few seconds after O2 went to zero, I had a several loud blasts. I've quickly closed the throttle to avoid any further damage.
I haven't found literally any error codes.
I suspect, there may be a problem with either:
- miss-firing and engine knocking (already done some work), or
- a fuel injection unit or a fuel pump

The roughness goes away, when the engine is running for some time (like 15-20 mins). Or at least was going, as for the moment I don't go on a long runs, just doing the garage works in a free time.
At a 1st glance I thought of an ignition coil, that it gets heated and evaporates the moisture out. But then I've quit the idea as the ride stays in garage, that isn't wet. Besides I have the relation - the higher RPMs are, the more rough operation.
I thought of a distributor timing, but yet, on idle it's more or less OK, and the problem persist with getting a higher rpms. The timing is done by a mechanical coupling, cannot change in functions of RPMs...

I don't have any info on the spider assembly. I thought of doing a:
- hydraulic circuit that would flow a cleaner
- electronic control unit to drive the injector
I would like to hear Your opinions. Thing is, on our polish market we have some basic things for Blazers available. I am getting my supplies directly from US, but it takes time.... too much time for an eager person like me.

Cheers, Mike

 

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Sounds like a wiring issue or possibly a bad sensor. If the O2 sensor is intermittently not sending a signal the ECM probably momentarily richens the mixture. Which could cause mis fires and when the unburned fuel in the exhaust does ignite it could make anything from a pop to blowing the muffler off.

 

Thanks for the reply.
I believe the O2 readings are accurate. On idle, the signal is steady, I have nice trace, w/o missing data.

I wonder if that could be related to a distributor. I had been removing the old cap for cleaning (my first thought) while I noticed, that one screw isn't torx20, but a Philips one. Then I found, that one of the cap mounting bracket have had been broken and glued to a cap. In a crappy way of course, as the bond was broken. I have ordered and applied a new one, which seats firmly, but things aren't OK yet.
I wonder, if the distributor rotor could spin off the center (on acceleration the engine swings) and miss one side of the cap pins. That would explain one bank misfire. Though, I am not very familiar with this distributor mechanical assembly.

Anxiously looking forward a new distributor set that should arrive around a new year's day.

Thanks for advice
Cheers, Mike

 

What do the misfire counters look like on live data?

George

 

Hm...
Good question George.
I went to a car with a OBD Dongle and Torque Lite. Got connected, started the engine to heat up and waited till it goes into a closed loop. Meanwhile I set the misfire plots for each cylinder. Since the fuel/O2 loop got closed, I've started increasing the rpms to see when the misfire counters start increasing. Strangely, but they don't. Just a flat lines. Neither the knock counter. Moreover, the engine did not run harsh as it was yesterday (wasn't smooth thou, I have had few quiet blasts and a little uneven operation). I could wind up to 6k rpms easily.

Your advice lead me to a conclusion it is not a misfire, or at least, it is not recognized by ECU as a misfire. I am not aware as a misfire detection mechanism works. I could swear it is, as it feels exactly like one.

Now it starts driving me crazy, as not only I have no idea what would that be, but I have no answer what conditions have changed it was +- ok for today, but not ok a day before. Need to observe that for a few days more.

Another thing is, that I found a record in a car documents, that this ride was running with an LPG installation for a while, but it was dismantled. That was a 1st generation of the LPG, that has an evaporator and delivers the mixture of oxygen and gas directly through the intake, not by the fuel supply system. I guess these problems I have on a petrol significantly increased with LPG installation that most probably blew up a plastic intake several times, so the owner decided to dismantle that... That would suggest it is not a fuel system. I am getting so confused now...

Cheers Mike

P.S. I suspect that some of the indicators available on Torque Lite app are not real, but a calculated value. Are they? If so, how could I distinguish the physical sensors from a calculated ones? Should I dig for a sensor map for my engine...?

EDIT: OH, yes, another thing You might ask me - my mileage; for the moment I have 112k. No overhauling I guess except some basic maintenance.

 

Misfires are counted when the crankshaft has a slight change in rotation speed near the firing of that cylinder so it is an implied fault and there is no indication of the cause. Either there are no misfires or the ECM is not detecting them properly.

What are your fuel trims at idle and again at 2500 rpm? Do they change abruptly when the truck starts to run like crap?

An O2 sensor voltage going to zero and staying there indicates an extremely lean mixture or a failure.

Have you done the fuel pressure/leak down tests? If so, have you left the gauge hooked up to see what is happening when the truck runs bad?

George

 

I don't believe that Torque Lite will read misfire counters. You have to use Torque Pro and also enable GM Enhanced PIDs in the the software. Before you are done with installing a new distributor you will want to check and adjust cam sensor retard. Torque is not going to do this for you. If you have 1998+ Blazer you can use Car Gauge Pro or Dash Command. If 1996/1997 then only Dash Command will work. Dash Command requires you to buy enhanced PIDs at $10 extra per vehicle. Car Gauge Pro does not require any additional purchase.

 

@GeorgeLG
Yet another good question. My respects! I am going to check the trims and if they're not zero I'll look for a possible leaks. I am truly grateful for pointing me into a right direction.
EDIT: I took a ride for a short trip with my mobile in a cradle and a Torque connected. Luckily, today it was running rough.
Here my observations:
On idle, the FT trims (dunno if they were LT or ST, that is unspecified in Torque, just a "FT/1" and "FT/2" plots) for both banks are zero.
On acceleration, up to 2k rpms, both trims are going positive up to 20%. I didn't want the mixture to go too lean and to avoid blasts I've did not go beyond 2k rpms, but I suspect it would go even further with triggering a MIL indicator.
On deceleration the trims are going negative with up to -20%.
Now I wonder if it is possible that I have a vacuum leak, as on idle the air leak would play a significant role and the trim stays around zero. I assume, the lower intake gaskets were never replaced, and as Christine stated lately, they are prone to break. I guess I should check the vacuum sensors now? MAF/MAT, etc or You'd have another suggestions?
EDIT 2: I have disconnected MAF sensor so the ECU would run on its map. The engine runs smoothly, as it never was before. I already gave a call to my supplier here, but he doesn't have MAFs on stock. Kindly asking what should be the pinout resistance, so that I could check if the resistors are OK. If they are, the cleaning should do the job. I also got an oscilloscope probe from a friend, so that I could check the traces of a high voltage that goes to the plugs and see if there are any problems with a distributor or an ignition system in general.
Thanks George, I owe You for Your help.

By the way, I have found an excellent video that explains the trims:
@Lesmyer
Well, my dongle is a WiFi type. I went through a Car Gauge Pro settings, but seems to me that only a blue tooth dongles are supported. So, is that correct I should get another dongle to run a Car Gauge?
To be honest, I have tried to search the difference in between Torque Lite and Torque Pro, but haven't found much of an info, neither on the developer's website. As I understand, the Lite version is somewhat limited to a Pro with the amount of a different indicators + the ads.

I am going to change the distributor anyway due to its condition. The prev. owner did a really "quality job" around with its cap mounting brackets.

 

Yes, Car Gauge Pro is Bluetooth only. Dash Command will work with WiFi but cost will be $10 + $10 more for enhanced PIDs for your vehicle. if you decide to buy bluetooth dongle, I recommend BAFX OBD2 as sold on Amazon for about $23. It is very fast refresh rate in comparison to most (~30 readings/second in Blazers). I once had a cheap Wifi adapter that did only 3 readings/second. This can be important when monitoring things that change rapidly like multiple misfire counters, O2 sensors, fuel trim readings, etc. Torque Pro does have a counter that displays scans/sec.

If you end up not using Car Gauge Pro (and you have purchased it), you can email and they will probably refund. They have done this for other people if Car Gauge Pro did not work for their particular application. Biggest argument for Car Gauge Pro is (as I understand it) is it will read and clear codes (not display PIDs or control) in ABS, SIR, BCM, TCM, other vehicle systems and you do not have to buy further licenses for each vehicle to get additional functionality. I do know that I can read and clear BCM codes on my 2004 Avalanche with Car Gauge Pro. Torque Pro will do Enhanced GM Powertrain PIDs as well as Car Gauge Pro, but Cam Sensor Retard is not supported - nor is reading/clearing of other system codes. Downside to Car Gauge Pro, is that it does not support Enhanced GM PIDs after CAN communication protocol was implemented (2006+) nor does it support Enhanced GM PIDs for 1996/1997 either - however it does support CAN protocol enhanced PIDs for the more modern Ford and Nissan. On 2006+ and 1996/1997 GM, Car Gauge Pro will only do the same things as Torque Lite. It's kind of hit and miss - but it works quite well with most of the Blazers.

All Torque Lite gives you is the ability to read/clear powertrain codes and monitor generic SAE PIDs which does include Fuel Trims and MAF and O2 sensors and coolant temp, etc but not misfire counters.

Even with a new distributor you still should check that cam sensor retard is 0° ± 2°. This value is an indication of proper alignment of the rotor with the cap as spark passes through. Ignition timing is actually determined by crankshaft sensor and PCM on this system, but the rotor still needs to point exactly to the right terminal or misfire can occur. This is a common cause of misfire in these Blazers. As long as factory hold down clamp has not been modified, the only possibilities for this being off include stretched/worn timing chain/gears, worn distributor gear, or excessive end-play for distributor shaft. If you get a P1345 after changing the distributor, it is in a tooth off.

It's your choice on what software to buy and use. I have Torque Pro, Car Gauge Pro, and Dash Command on my cell phone. I have HP Tuners VCM Scanner and Scan XL Pro on my Windows notebook. I have found a use for each and every one, at one time or another. I find the Scan XL Pro to be the least value for the money, but it does do Enhanced GM PIDs using CAN protocol on my 2006 Pontiac - so even it has it's purpose. Only cheap software that could do the same was Dash Command.

Finally - Positive fuel trims mean that system is adding fuel over the factory calibration in an attempt to correct fuel mixture. A vacuum leak would tend to affect fuel trim at idle far more than at RPM. +20% would mean that pulse width of injectors has been increased 20% over factory calibration in order to make mixture give correct O2 sensor readings. FT of zero (no alteration of factory calibration) would tend to mean no vacuum leak (unless system is going to open loop and not controlling the fuel mixture at all). O2 sensor readings would tell.

Better I think to get your distributor in and some good software besides Torque Lite before coming to any conclusions.

I still don't remember you telling us what year Blazer you have.......

Good luck and best wishes

 

Thanks Lesmyer for a detailed info on the differences in between Torque and Car Gauge. It is more clear and detailed than the info I found on a developer's website
I find it a bit downing the Car Gauge does not support WiFi standard. I've chosen a Wificause I expected it to be more handy - it might be also supported by some laptop software, as mine does not have a BT. And could possibly offer a higher data transfer.

Nevertheless, I don't like half measures and these dongles cost next to nothing. I have already ordered another one with a BT and I am going to go for a Car Gauge Pro.

As for checking the timing settings, I am going to check it with Car Gauge as You have mentioned, and record the value just in case. Next, I am going to replace the plugs for an AC Delco iridium set I have recently received. Removing a plug that goes behind a steering column is a pain in ***, so I think I'll combine that with a distributor swap (and a compression test). I'll bring the 1st piston to DTC and see what I find on a markers under the cap. For the moment my distributor does not seem to be a problem, as with a MAF disconnected, when the engine runs in an open loop, it is all perfect.

I have borrowed an oscilloscope probe that taps to a plug wire and allows You to observe the ignition pulses. It is a very similar to this one:
Automobile spark plug oscilloscope probe
I expect that this probe is going to be more handy than info delivered by ECM, as You see the analog readings of a pulses, so their shape and width. Digital is digital - it counts the pulses but does not refer to their shape. I may drop some photos here if anybody likes.

For the moment I'd need an info of the MAF resistor values, so that I could check if mines is OK. If it's busted I'll get a new one, but I want to make sure 1st. Maybe they are covered with a thin film of some crap that prevents a good heat dissipation and cleaning with an alcohol would be enough.

Cheers, Mike

Oh, and regarding to my ride, all the details are in my signature: Chevy Blazer '00 4X4 4D LT. I am not gonna need the extra features of OBD from 2006+