Chev / GMC Misfire, poppet injector diagnosis, troubleshooting and replacement

[DFergyferg]

I have a 1999 Chevy Suburban 454 7.4L Vortec. This video was extremely helpful, thank you!

[markjhicks]

@DFergyferg Thank you for the feedback, it really does mean a lot to us!

Take Care,

Mark Hicks

Wells Vehicle Electronics

[Elricck]

blah bla bla blah blah

[66bubbaray]

continud,, she was running perfect then later that day bein it was the weekend me an my cousin went duck hunting again and when i got back (you guessed it) she wouldnt start again ,,and fyi when i was duck hunting i was at cousins house (bein he lives right next to the bayou) for the whole weekend so it would be two or three days that she wasnt being driven don't know if that helps

[markjhicks]

@66bubbaray Ok if it has spark it means the Crank sensor is working. If you spray carb cleaner of starting fluid into the intake will it start? If it does it means it is lacking fuel. If the fuel pressure is good like you said, the next is to check the quality of the fuel. If that looks good the next is to check the injector circuit. the intake will have to come off to do this. Let me know the results and I will help you from there,

Mark Hicks

Wells Vehicle Electronics

[66bubbaray]

the odd thing about it is the second to last time drove her she was running with the miss as usual then my cousin picked my up to go duck hunting one weekend and when i came back she wouldnt start then my uncl had thought it was the crank shaft pos sensor so he went ahead and bout it for me we changed it an tried to get her running but nothin later on we jus tried to turn her over jus to hear what she was doin again and she jus started brought her home put on a scn tool and it said she was perfe

[66bubbaray]

@markjhicks ya we done checked she has spark and the fuel pressure is around 60 something

[66bubbaray]

hi i have a 97 gmc sierra with the 4.3 she always had a misfir but she got me from point a to point b and now she wont start. me an my cousin who is curently in school for auto mechanics have begun to thnk it is the fuel injectors. we put her on a compter a while back and it showed a randm misfire code and that it ran lean(ther were 2 more codes cant remember them) she startd getting worse over time typically we i didnt run her for a few days. could the problem have gotten so bad she wont start

[markjhicks]

@66bubbaray The first thing I would do is check for spark and fuel pressure. When you get these results let me know. You can also call me on our tech line 1-800-558-9770 from 7 am to 7 pm CST.

Mark Hicks

Wells Vehicle Electronics

[townkevin59]

I have the same 4.3 6 cylinder engine in my 96 Chevy pick-up. This is the worse engine, I have constant problems with it, I have replaced the distributor 5 times, there is rapid misfire codes, NO power with towing (Small trailer) and on and on. Now my truck won't start at all and I'm ready to shove it over a cliff. I have never hated an engine like i do the 4.3 ...It is JUNK and I give up on it!

[JockyTy]

@markjhicks Thank you so much, ive been having non stop problems with my blazer and just want it to run strong again. ill try the carb cleaner later today.

[JockyTy]

Again sorry, I'm having a Randy cylinder misfire. I dont know what else to do or could be causing this. I've replaced the rotor, cap, wires, plugs and injectors. I was told I need a new upper intake gasket. Could that solve my problem? Please help!!

[HOTRODRICO]

@JockyTy IGNITION COIL..

[JockyTy]

Sorry didn't mean to post two post.

[markjhicks]

@JockyTy An Intake manifold leak is common on your vehicle. Could this cause a P0300? Yes! If you do not have a smoke machine, try spraying carb cleaner around the intake while the engine is idling. If the RPMs change due to the addition of the carb cleaner around the intake it means you have a leak.

Good Luck

Let me know if you have any further questions.

Mark Hicks

Wells Vehicle Electronics

[JockyTy]

@markjhicks thank you ill try the carb cleaner later today. The only other problem im having is this look up the video "CHEVY BLAZER LS 4X4 WHEEL NOISE 50-70 MPH" ????? i cant figure out what is causing this. if i put it in 4 hi it goes away please let me know what you think

[markjhicks]

@JockyTy I am sorry I would like to help you but i truly am not a drivetrain expert. If I were to guess i would think it is something in the sync between the front hubs and the transfer case.

Mark

[JockyTy]

I have a 2000 zr2 blazer 4wd 4.3

[dtrspre]

decent video, got one to cover a 97 astro?

[markjhicks]

@dtrspre No sorry this is the only injector video we have so far.

Mark Hicks

Wells Vehicle Electronics

[frank0067]

also he said there was ample compression and spark in the wires but the pulstar was wet meaning didn't get ignited ..but we tried 2 new pulstars prior ..only when he put champion in, it did ok.. so when i went home i triggered another misfire by putting back pulstar in #4 cylinder, so i am left thinking that the computer or coil cant handle the capacity of the pulstar plugs ..anyway i went and undid that by putting back the ac delco into #4 .but the misfire light hasn't gone away yet !

[markjhicks]

@frank0067 Either the plug is not firing or the cylinder is being flooded ... possible injector problem. Let me know what happens.

Mark

[frank0067]

i am misfiring on cylinder #1 .. a V6 venture 1998 .. mechanic changed plugs and wire set already, but its still there, this cylinder is behind near firewall hard to reach..

oil looks clean, exhaust too.. new plugs triggered this issue

is there an easy way to test this #1 injector in this van without ripping taking apart other things?

[markjhicks]

@frank0067 When you new plugs set off this misfire, I am assuming you mean it was OK before the plugs were replaced. In that case my first thought , did you replace the plug again or swap it for another cylinder? Second, was conductive anti-seize compound used? When checking the injector, first check to see if the computer is firing it with a noid light. Another way is to listen to it with a screw driver to your ear. Listen for a clicking sound this would indicate the injector is firing.

Mark

[frank0067]

@markjhicks

yes i did swap the new pulstar with another new pulstar that was working from cylinder #4 and put it into cylinder #1 but still the same thing happened.

now this morning i took my van into large outfit ..that mechanic said he put a champion plug in cylinder #1

and everything was great no light no misfire.. so i drove it home..remembering i had a delco plug in cylinder #4 .so i changed it to pulstar, but a misfire came back, not sure which misfire this time.

[maycor1076]

Time is money! why hook up a smoke machine and checking power at the injector connector? You got the CO reading very hi fuel problem look at lambda. If you had a vaccum leak fuel trim would show lean for both banks as well as misfire/no start if no power to spider. CO high next hook up fuel gauge do a injector balance test and it would show leaking injecor in the gauge. this should only take 10 minutes. Very good video by the way. Keep up the good work.

[markjhicks]

@maycor1076 You are right looking at Lambda would have helped. However like you said not many shops have this equipment, so we decided to stick with mainly the HC and CO readings. Hooking the noid light to the harness took only a few minutes to confirm the PCM was triggering properly. I am pleased you liked the video. We are working on some as we speak I am sure you will also enjoy.

Take Care

Mark Hicks

[lillen300]

@markjhicks I miss sarge XD he was awesome with capital AWESOME!

[maycor1076]

Looking at the the video you can see having the right equipment, information and knowledge is a must in the automotive field. Let me break it down. Oem Scan tool Tech II $4,500 Snap on Scan Tool Modis $6,500 Gas analyzer for Modis $5,500 Smoke Pro $950 that does not include updating/oem subscription/auto information data. Not every shop or dealership have these combination. This is why shops charge accordinly.

[maycor1076]

Looking at the the video you can see having the right equipment, information and knowledge is a must in the automotive field. Let me break it down. Oem Scan tool Tech II $4,500 Snap on Scan Tool Modis $6,500 Gas analyzer for Modis $5,500 Smoke Pro $950 that does not include updating/oem subscription/auto information data. Not every shop or dealership have these combination. This is why shops charge accordinly.

[nobleheight]

Can you run an electric motor on AC without first converting it to DC?

[markjhicks]

I am not sure where you are going with this...but yea I have a table saw, planner and joiner that do.

[nobleheight]

The electric motors I read about in howstuffworks website run on DC. I was just curious whether electric motors also run on AC, and if they are designed differently.

[nobleheight]

Oh wait. I just found a wikipedia article about AC induction motors. I didn't even think they existed before this.

[nobleheight]

I know a test light should definitely not be used to test an air bag; however, I don't understand why a voltmeter is okay while at the same time an ohmmeter is not okay. What is different about a voltmeter that makes it okay while a ohmmeter, not okay?

[markjhicks]

An ohmmeter works by send a small aount of current from one lead and calculates the resistance in the circuit by how much of that currents flows through. Sending even a small amount of current through an air bag circuit is not recommended.

[nobleheight]

Okay, but what about test lights. Test lights don't send current, but they are prohibited from testing air bags. Are only powered test lights prohibited then? Maybe regular test lights are okay?

[nobleheight]

telephone pole transformers

[nobleheight]

Is carbon a conductor or an insulator? Because I read that carbon tracking (on COP) seems to work as a conductor and yet fouling on spark plugs (oil is made of carbon) seems to work as an insulator. I think oil is also used on telephone transformers as an insulator (for cooling or something).

[Wellstech]

It depends upon how the carbon was formed and the type it is. For example diamonds are one of the best insulators, where graphite also made of carbon, is one of the best conductors.

[nobleheight]

Now, I think the answer is A, but I am not sure.

A compression test shows low compression in one cylinder. A cylinder leakage test is done and there is no leakage in any or the cylinders. What is the most likely cause of the low compression in the one cylinder?

a. worn cam lobe

b. burnt exhaust valve

c. leaking head gasket

d. worn valve guide

[markjhicks]

A is the correct answer

B would show leakage

C would also show leakage

D would not cause low compression

[nobleheight]

When removing an alternator, I understand why you have to disconnect the battery ground cable, but I don't understand why you have to wait for the air bag system disable. The alternator is no where near the air bag.

[markjhicks]

Any voltage spike in the system could set the air bags off. Disconnecting the battery cuts the odds of this occurrence,

[nobleheight]

In a regular circuit, if resistance goes up, voltage goes down.

But it seems the opposite is true if there is a gap in the circuit such as in a secondary circuit. If resistance goes up, then the firing line voltage goes up as well. Unless I am wrong about that.

[markjhicks]

I believe you are correct. The voltage needed to bridge an air gap goes up as the gap width increases. Because the wider the air gap the more force is required to ionize the air within the gap. This is a good question.

[nobleheight]

Will low compression increase secondary resistance?

[markjhicks]

Low compression will decrease secondary resistance.

[nobleheight]

I just found the following info that stoichiometry is different for different fuels. There is a BP gas station that I buy gasoline from that says their fuel is 10% ethanol. I assume that means it is E10. So I guess that means stoichiometry for my car is no longer 14.7 then. It is actually 13.8:1. Is that correct? But then how does my PCM even know enough to compensate for that? It's not like I pressed a switch on the dash to tell it.

Gasoline=14.7:1

E10 = 13.8:1

E50 = 11.2:1

E85 = 9.6:1

[markjhicks]

If you dont have a flex fuel vehicle the computer will compensate for E10 through fuel trim adjustments. On a flex fuel vehicle there is a sensor to tell the computer alcohol content. Go to the Wells website and read the newsletters Volume 11 issues 1 and 2 Present & Future Power trains - are you ready? This is covered in them.

Mark

[nobleheight]

If alcohol content in the gasoline skews fuel trim adjustments, then wouldn't that confuse a technician looking at the fuel trims, making him think the engine is running rich or lean? By the way, which one would it be, rich or lean, if alcohol content is increase?

[nobleheight]

Will too much ethanol content in the gasoline cause the MIL to come on and for what DTC?

[nobleheight]

How do you connect a fuel system pressure gauge to a fuel system without a shrader valve?

[markjhicks]

You will need to connect through the line. Usually this is done at the throttle body.

[nobleheight]

If a spark plug is fouled, will that increase or decrease secondary resistance?

[markjhicks]

That will increase secondary resistance, because it will take more current to bridge the plug gap.

[nobleheight]

If a spark plug insulator (ceramic) is cracked, will that increase or decrease secondary resistance?

[markjhicks]

If it is cracked and shorting to the engine block the secondary resistance will decrease.

[nobleheight]

On a 4-stroke engine, completion of 4 strokes is one cycle. Looking at one cylinder only, does the PCM pulse the injector only once per cycle (4 strokes). Or does it break it up into multiple pulses per cycle (4 strokes)?

[markjhicks]

It depends upon the strategy being used by the computer system. On today's vehicles the injector will fire once. On some earlier vehicles that would gang fire the injectors it could fire several times.

[nobleheight]

Fuel trim modifies base injection time to arrive at the final computed injection pulse width.  We know fuel trim changes, but what about base injection time? Does base injection time change based on factors like engine load, RPM, TPS, MAP, and MAF?

[markjhicks]

Yes it does. This is called injector pulse width. This is the amount of time an injector is held open allowing fuel to spray. The longer the pulse width the richer the combustion.

[nobleheight]

Wait a minute. Let me try to get my terminology straight.

If fuel trim is 0%, then base pulse width equals actual pulse width.

Is this correct?

[markjhicks]

Yea that sounds reasonable.

[nobleheight]

Wow! I just found a web page that describes how injector pulse width is calculated. In addition to fuel trim, what they call base injector pulse width is also modified by factor A and factor B. This is from the "How Stuff Works" website. I am actually surprised they went into such detail for a site intended for the lay masses.

[nobleheight]

If a fuel pressure regulator is working properly, will fuel pressure increase or decrease if the fuel return line is restricted? If it is restricted what will the symptoms be?

[markjhicks]

Running rich and pressure would go up if the return line is restricted.

[nobleheight]

One cylinder has no spark. The coil-on-plug assemby is checked.  The connector is back probed and the multi-meter reads 0 votls. The most likely cause is

A. open primary coil.

B. open wire going to primary coil

C. carbon track in tubing going to spark plug.

D. faulty switching circuitry.

[markjhicks]

From what you said it appears to be B.

[nobleheight]

Is a popping sound heard at the throttle body caused by a stuck open intake valve?

[markjhicks]

Yes it could be.

[nobleheight]

The vacuum gauge has a reading of 1 inch of Hg while cranking the engine.  What is the most likely cause?

A. partially restricted exhaust system

B. restrict air inlet

C. stuck open valves

[markjhicks]

any one of the above.

[nobleheight]

If an EGR valve is stuck open, will the engine hesitate upon acceleration or will the engine smooth out upon acceleration?

[markjhicks]

If the ports and EGR are open the engine will not idle. The EGR momentarily opens upon acceleration.

[nobleheight]

Will an RPM of 650 cause a misfire due to low idle? Is that number low as far as idle is concerned?q

[markjhicks]

Should not cause a misfire but it is low.

[nobleheight]

What setting should the multi-meter be set at when checking for alternator diode ripple? ac volts or dc volts?

[markjhicks]

No more than .5 volts AC.

[nobleheight]

What is the most likely cause of an inability to fill the gas tank above half way?

[markjhicks]

Ventilation problems.

[nobleheight]

Is liquid gasoline pouring out of the EVAP canister caused by overfilling the gas tank? I think this happens a lot on Hyundai Elantras.

[markjhicks]

It could be.

[nobleheight]

Have you ever heard of such a thing as a fuel-limiter solenoid in the gas tank? What does it do?

[nobleheight]

On a vehicle with 4 wheel independent suspension, is it possible for a misaligned front cradle/subframe to cause the rear alignment to be off in any way?

[nobleheight]

How do you calculate thrust angle (from the rear wheel toes) if the toes are not the same between the left and right rear wheels? Do you add both toes and divide by 2?

[nobleheight]

Will adjusting camber on the rear right wheel on a vehicle with independent suspension also affect the toe on this wheel (meaning you have to check toe also whenever you adjust the camber.)?

Would the answer to this question change if the vehicle had non-independent rear axle?

My understanding is that if rear toe changes, the thrust angle would also change, making a check of the front toe necessary. Is this correct?

[nobleheight]

Do the new AFR sensors have to be hot to work like the old oxygen sensors?

[nobleheight]

Does this 1997 GMC Jimmy have secondary air injection?

[markjhicks]

I dont think it does.

[nobleheight]

Is short term fuel trim an average value or an instantaneous value?

Is long term fuel trim simply an average of fuel trim values over a long period of term?

Is short term fuel trim simply an average of fuel trim values over a short period of time?

[markjhicks]

OK, here is a very skinny explanation of fuel trim. Short term fuel trim (STFT) pretty much follows the O2 signal. When the average of the STFT is 0 the long term fuel trim (LTFT) stays at 0 also. When the STFT averages lets say, +10 the LTFT will start to go negative or take fuel away until the STFT averages near 0 again. 0 is 14.7 to 1.

Hope this helps,

Mark

[nobleheight]

I was watching a Bergwall training video that shows you how to test the electrical integrity of a fuel injector coil using a lab scope.  The lab scope they used was an OTC Vision. One thing I noticed that I thought was weird was that the wave form displayed did not scroll even as throttle was opened. As the throttle was opened, you could see the injector pulse width widing as RPM increased.

[markjhicks]

They may have been using the injector as a trigger point to keep it steady. Were they looking at voltage or amperage draw?

Mark

[nobleheight]

voltage.

[nobleheight]

The intake is leaking antifreeze? I didn't know coolant flowed into the intake assembly? I thought we want the intake to be warm, not cool.

[markjhicks]

Anti-freeze does flow through the intake to help fuel atomization. On very early vehicles it would also help heat the choke spring. The coolant will be warm, it is on the heated side of the thermostat.

Mark

[nobleheight]

You could tell that the PCM is pulsing properly just by eye-balling the noid light?

[markjhicks]

Yes, if the noid light would stay on we would know the PCM was holding the injector open.

Mark

[nobleheight]

It seems to me that the diagnosis of a bad fuel injector was made using the process of elimination. There was no direct observation. If you guys had a five gas analyzer handy, you could have removed the spark plug and stuck the gas analyzer probe into the combustion chamber to test for the presence of HC.

[markjhicks]

You are right the injector was diagnosed by eliminating everything else. This injector system is not really accessible for accurate diagnostics. Putting the 5 gas probe in the spark plug hole would always show a presence of HC. This would not be a valid test.

Mark

[nobleheight]

In my opinion, if cars had HC sensors in addition to oxygen sensors, then the PCM could ascertain a misfire. However, this would increase the price of the car.

[markjhicks]

There isn't any HC sensors that would last very long constantly subjected to all the elements...that I know of...nice thought though. The challenges of when too much oxygen should be ignored has sparked the creation of the air / fuel ratio sensor. In future videos we will be discussing this topic.

Mark

[nobleheight]

Why doesn't the current signal from an air/fuel ratio sensor fluctuate like the voltage signal from a regular oxygen sensor?

But then again, why does the signal of a regular oxygen sensor fluctuate to begin with? What does the frequency indicate? Does the frequency increase with engine RPM?

[markjhicks]

An O2 sensor signal oscillates because as the sensor is reporting a rich signal for example the computer is reacting by leaning the system. Stoichiometric of a 14.7 to 1 ratio is obtained through an average.

Mark

Mark

[nobleheight]

Signals from an air/fuel ratio sensor as display on a scan tool in a "normalized" form is really backwards.

On a normal oxygen sensor, values below 0.5 are lean and values above 0.5 are rich.

However, it is the exact opposite for air/fuel ratio sensor values displayed in normalized form.

Looks like whoever decided to flip that is evil. This can lead to falsely condemning sensors or even the PCM.

[markjhicks]

In the future we will be producing videos with air/fuel sensor diagnostics. There really is not enough room here to give it the explanation it deserves.

Mark

[nobleheight]

"It looks like bank 1 is lean"

The key words is "looks like."

Isn't it ironic? The reality is that the air/fuel ratio is rich due to a leaking fuel injector, and yet the stupid PCM thought the air/fuel ratio is lean and made a false correction.

Stupid computer!!!!!!!! Somebody needs to make a computer system that can ascertain a misfire.

[markjhicks]

It is because the oxygen sensor looks at only oxygen levels.

[nobleheight]

Please correct me if I am wrong.

Misfires increase oxygen levels in the exhaust, which fools the PCM into thinking the engine is running lean, which explains why the PCM is commanding rich.

Am I right?

[markjhicks]

You are right, however with OBDII things have gotten better. Early OBDII systems like this will only allow a limited amount of change, like the 25% percent. On later systems, when the change becomes too great, the system will revert to learned values, preventing for example a catalytic converter failure.

Mark