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Mark
Mark, ASE Certified Technician
Category: GM
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Experience:  34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech
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1999 gmc suburban: distributor..the rotor and cap..screw

Customer Question

my 1999 gmc suburban's distributor was having problems so i attemped to replace the rotor and cap only to find the screw tabs were broken and the cap was loose. I have gone through all the appropiate steps and replaced the distributor but the engine will not start. What am I doing wrong?!?!?
Submitted: 4 years ago.
Category: GM
Expert:  Mark replied 4 years ago.
Greetings, my name is Mark.

You will need to set up your timing. You should do this even if you're sure you installed the distributor correctly.

First, you need to bring the engine up on the number 1 cylinder compression stroke. The spark plug closest to the radiator on the driver's side is number 1. I don't mean to insult you here, but I have no way of knowing what you know, OR what you did.

Anyway, hold your thumb or finger over the hole while an assistant carefully "bumps" the engine. You will feel the pressure on your thumb when the piston is on the compression stroke.

As you get close, look down at the harmonic balancer and align the line on the balancer with zero on the timing indicator. It is usually the biggest "cut-out" of the indicator. You are now on number 1 compression stroke.

Remove your distributor cap and make sure your rotor is pointing to number one plug wire. If you are off, you will need to remove your distributor and align.

All of this is pretty straight forward and not difficult. The difficult part will be aligning the distributor with the "oil pump drive". That is what I think happened when you pulled the distributor out. The oil pump drive moved and you put your new distributor and it would not set down. You continued to move the rotor to make it fit and set down. Thus, your timing is off.

Anyway, I don't know. I may be way off track here. What you will need to do is find a long flat bladed screwdriver and move the oil pump drive until it will align with your distributor so as the rotor is pointing to the number 1 plug wire.

You didn't give a whole lot of info. here and I am kinda assuming some stuff.

Hope this helps,
Mark
Customer: replied 4 years ago.

Thank you Mark, I understand but on my motor the timing indicator on my engine is different than any I have seen. It is just a small hump with a v grove cut in it. Is this the zero time mark.

Expert:  Mark replied 4 years ago.
Hello back.

Yes, anything that looks like some kind of indicator. The reason being because you're not suppose to be able to actually set the ignition timing like we could in the olden days.

What we do at the shop is elongate the fork that holds the distributor down. Then using a TECH II GM scanner, we can actually set "crankshaft variation" and fine tune. The chevy engines of this sort seem to like zero for a timing set. Spark knock is terrible if set advanced and hard starting is an issue too.

Anyways, for you, not too worry. You'll be okay with the original set. You just need to verify your "base" timing is correct. Just bump the engine around until you feel the pressure. Then using a socket on wrench, (5/8) go ahead and bring up the line on the balancer to align with the V. (Using the harmonic balancer bolt)

At this point, you just want to be as close to TDC as possible. Who knows, you may do all this, and when you pull the cap off, the rotor might be right on. At least then you will know that you have other issues. You will know your "base" timing is correct.

Let me know if I can answer any other questions. And let me know how you make out.

Take care and hang in there
ME
Customer: replied 4 years ago.
Thanks again for your help Mark just one more question and I think we will have it. If the timing is close enough will I need to take it to a shop in order to bring it into the correct time or can I do this at home?
Expert:  Mark replied 4 years ago.
And greetings again my friend,

No, I wouldn't worry too much about the final timing. You drive your truck and you know how it is suppose to act. If you do experience "spark knock", "hard-cranking" effort, or "long cranking" effort, then it probably should be done.

Most of the time, you should be good. I was kinda rambling on there about fine tuning and I didn't need to. Below, I have included the timing procedure as it is outlined for us. You can read through-it and at least you would know what you're talking about IF you should happen to want to have it done later.

I think I called it a variation learn, when it is really an offset learn.

HEY, take care and I am happy I could help.
Let me know if there's anything else.

Camshaft Retard Offset Adjustment

Test Procedure

You cannot adjust the ignition timing. You may need to adjust the distributor in order to prevent crossfire. To insure proper alignment of the distributor, perform the following:

  1. With the ignition OFF, connect the scan tool.
  2. Start the engine. Allow the engine to idle until the engine reaches the normal operating temperature.
  3. Important: The Cam Retard Offset reading will not be accurate below 1,000 RPM.

  4. Increase the engine speed to 1,000 RPM while performing the following steps.
  5. Use the scan tool in order to monitor the Cam Retard Offset.
  6. If the Cam Retard indicates a value of 0 degrees, the distributor is properly adjusted.
  7. If the Cam Retard does not indicate 0 degrees, the distributor must be adjusted.

Adjustment Procedure


    Object Number: 18446  Size: SH
  1. With the engine OFF, slightly loosen the distributor hold down bolt.
  2. Important: The Cam Retard Offset reading will not be accurate below 1,000 RPM.

  3. Start the engine and raise the engine speed to 1,000 RPM.
  4. Use the scan tool in order to monitor the Cam Retard Offset.
  5. Rotate the distributor as follows:
  6. To compensate for a negative reading, rotate the distributor in the counterclockwise direction.
    To compensate for a positive reading, rotate the distributor in the clockwise direction.
  7. Repeat step 4 until 0 degrees is obtained.
  8. Turn OFF the ignition.
  9. Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

  10. Tighten the distributor hold-down bolt.
  11. Tighten
    Tighten the bolt to 3 N·m (25 lb ft).

  12. Start the engine.
  13. Raise the engine speed to 1,000 RPM and view the Camshaft Retard Offset.
Mark, ASE Certified Technician
Category: GM
Satisfied Customers: 840
Experience: 34+ yrs Dealership Exp. - Fully State & ASE Certified - GM Master & GM World Class Tech
Mark and other GM Specialists are ready to help you
Customer: replied 4 years ago.
Mark hey its me again. Still something wrong with my suburban. Its now up and running but not driveable. When you accellerate it still sputters until u let off the gas. What have i missed???
Expert:  Mark replied 4 years ago.
.....and a hello back my friend.

I am going to be honest and tell you I have no idea what could be wrong. There could be a dozen different things going on. I have no idea if you indeed did set up the timing correctly.

You haven't stated in your post what you did. This was a couple weeks ago, and I don't know what all you have done the last couple weeks.

Sounds to me like you might still be off on the timing. Can you explain to me what you did find and how you corrected it?

I am not there. When we're doing this through e-mail, it is extremely important to include everything that's going on and be as specific as possible.
Customer: replied 4 years ago.
I did as you explained. I brought the #1 cyl to tbc then removed the new distributor and reinstalled it with the rotor pointing at the #1 spark plug wire. When I tried to start the engine it would not start so I brought the #1 cyl to tdc again and removed the distributor again and went back one tooth on the cam. The engine would start but ran rough, so I repeated the process again and went back one tooth again. The engine would start and was smoother at idle but when I attemped to drive the engine would sputter. I noticed during one of the times I was bringing the #1 cyl to tdc that the coil arched from the side so I have now replaced that and the spark plugs just to be on the safe side but still the engine sputters when attempting to drive. I have also replaced the fuel filter. Since I had to replace the distributor I could not place reference marks on it or the engine for reinstallstion. When the engine is idling it will decrease and increase rpm slightly also. I have a clean air filter and am now at a loss. What would you suggest to be my next step??? Thanks in advance for all of your help.
Expert:  Mark replied 4 years ago.
Okay, I know you are explaining to me the best you can and I appreciate that. I did notice that through-out your post, you did not say you brought the engine to TDC, "compression" stroke. There is an exhaust stroke and a compression stroke.

Also, you said you saw the coil arch, so I am going to assume you were "bumping" the engine with the key on. I am here to tell ya, your rotor should be on the number 1 spark plug wire when the piston is on the number 1 compression stroke. If it was done properly, you shouldn't have had to move it one tooth.

It really can only be the timing. You did nothing else. The fact that the truck ran different each time you messed with the distributor, tells me it cannot be anything else. Why would we want to even consider anything else? You're getting fuel, we know that.

When you brought the timing up to TDC, how did you know when to stop? How did you know whether you went too far or not far enough? How did you know whether you were on the compression stroke or exhaust stroke?

If we lived close by each other, and I came over to help you, I would ask what you did. I would then want to double check your work. I would remove the spark plug and then have you bump the engine until I felt compression.

I would then ask you for a 5/8" socket and rachet. I would either put a small long piece in the spark plug hole, (like a pencil) or look at the harmonic balancer. I would continue to move the balancer until the XXXXX XXXXXned up, or the pencil started going down, rather than up.

I would then remove your dist. cap and see where the rotor is. I would CONFIRM your repair. After I lined up the rotor, I would CONFIRM that you had all the spark plugs wire in the proper firing order.

Once all that was done, I would start the engine, and if it ran rough, I would see how much movement I could get out of the dist. WHILE it was running and see how that effected the running. If you have a timing light, put it on number 1 and see where it is firing on the harmonic balancer. I know you said your marker down there was funky, but do the best you can.

Double check your work and move the distributor a little one way or the other while it is running. Leave the dist. hold down bolt just a little loose so you can move the dist. You'll notice that when you move the dist., it may take the engine a couple seconds to react. Don't move it much. Experiment.

I don't remember. Do you have a timing light?




Customer: replied 4 years ago.

Goodmorning Mark, I did as you explained to bring the #1 cyl to TDC. I had my son bump the ignition until I felt pressure on my finger at the #1 cyl and then looked at the harmonic balancer for the timing mark and finished rotating it to the timing hump on the block. When I first started this after speaking with you I realized I had installed the distributor incorrectly it was somewhere close to the #8 firing position and of course the engine would not start. I corrected that and the engine started. I have traced all the plug wires to be certain that the firing order is correct and it is.

 

To recap this is a 1999 GMC Suburban 5.7L. To clearify, when you said the rotor should be pointing at the #1 spark plug wire, do you mean the actual wire where it connects to the distributor cap or to the contact post in the distributor?

 

Also, I am not sure if I explained but the engine at idle seems to miss or skip every so often, could this be due to a faulty spark plug wire? I may have not explained earlier that all these skipping problems started when I put a small amount of gas in the tank, but all that gas has been replaced with fresh gas (super unleaded). Not sure if that was important.

Expert:  Mark replied 4 years ago.
.....and good morning to you too.

Okay, here we go. First of all thank you for being patient as we try to do as best as we can communicating.

Your dist. rotor should be pointing to the Number 1 plug wire. I know when you look under neath the cap, it looks all goofy. The number 1 cylinder is driver's side, front. Right behind the PS. I know you know that, but I want to make sure we both understand each other.

That wire should go up to the cap and attach on the driver's side. Should be 4 wires sticking out. Now if you look at the underside of the cap, It may be firing on the left side or where ever, you just need to put the rotor where ever the number 1 is firing.

It would be kinda rare for the plug wires to be bad, however not totally impossible. If you could get the truck to run, you could try brake torquing it, and then take a spray bottle with water and spray your plug wires at the spark plugs. You will hear or see spark to indicate a bad plug wire.

The gas type is not important at this point. You get this thing running decent, you just need regular gas though. This running, skipping, and missing thing stills leans me very seriously on ignition. Something with spark here, we're missing.

You doing a great job explaining things as we go along here, but do you have a timing light? And did you try to get this running and move the dist. while it was running?

I am here for a little bit this morning, but then I will be in and out all week-end.





Customer: replied 4 years ago.
Thank you for your patience here, the rotor should point to the point where the plug wire connects to the distributor cap, meaning at TDC the spark has already been sent to the #1 plug or in the direction of the #1 plug at the front of the motor? Also my code reader says that my MAF or VAF A ckt low Input and Cam Position Sensor A Bank 1 Ckt Malfunction. No I do not own a timing light should I go buy one.?
Expert:  Mark replied 4 years ago.
Hello back. ..

I am beginning to wonder whether we're communicating. You say the plug wire should point to the point where the plug wire is attached. I have to say NO to that. Remove the distributor cap and look underneath.

Doesn't it look like a spider web in there? The cap underneath will have all 8 little nubs in a circle. You need to look at number 1 spark hole, (where the wire attach's), then turn the cap upside down and trace that connection to the little nub on the cap.

The little metal nub will not be right by that hole. I hope this makes sense. If it doesn't, we need to make sure we are on the same page here.

Also, below I have included some descriptions for the codes that are showing up. You will notice the cam sensor codes are related to your timing. The cam sensor itself is located inside the dist. You timing needs to be on for this to work. It fires the injectors at the right time when your timing is correct.

Your mass air sensor could also be related, maybe not. Right now you need to have your timing on before you start diagnosing any other problems.

I wouldn't run out and buy a timing light. At least not yet anyway. Get this timing on, and then see if moving the dist. a little one way or the other will help.

By the way, you say your engine is missing a little or running erratic. Well, this makes sense with your timing being off. The injectors are not being fired when they are supposed to.




Mass Air Flow (MAF) Sensor


Object Number: 325359  Size: SH

The mass air flow (MAF) sensor measures the amount of air entering the engine. The VCM uses this information to determine the operating condition of the engine in order to control the fuel delivery. A large quantity of air indicates an acceleration. A small quantity of air indicates a deceleration or an idle.

The scan tool reads the MAF value and displays the MAF value in grams per second (gm/sec). At idle, the MAF value should read between 5 gm/sec - 7 gm/sec on a fully warmed up engine. The values should change rather quickly on acceleration, but values should remain fairly stable at any given RPM. When the VCM detects a malfunction in the MAF sensor circuit, the following DTCs will set:

DTC P0101 System Performance
DTC P0102 Frequency Low
DTC P0103 Frequency High


Camshaft Position Sensor

The scan tool scan tool will display camshaft position sensor data as a 0 and 1 as the sensor pulses, the scan data will switch from 0 to 1. All camshaft position sensor data should be checked at idle. An error in the camshaft position sensor circuit should set a DTC P0340. The camshaft position sensor sends a signal to the VCM which uses it as a sync pulse to trigger the injectors in proper sequence.

Cam Signal

The VCM uses this signal to determine the position of the #1 piston during its power stroke. This signal is used by the VCM to calculate fuel injection mode of operation. A loss of this signal will set DTC P0340.

If the cam signal is lost while the engine is running, the fuel injection system will shift to a calculated fuel injection mode based on the last fuel injection pulse, and the engine will continue to run. The engine can be restarted and will run in the calculated mode as long as the fault is present .



Distributor


Object Number: 12796  Size: MH

The distributor is actually an assembly that contains the camshaft position (CMP) sensor, the cap, the rotor, and the shaft. The distributor is splined by a helical gear to the camshaft and rotates providing a spark to each spark plug wire. When servicing the distributor, it is critical to ensure proper cap sealing to the distributor body and correct installation to the camshaft. If the distributor is installed a tooth off in relation to the camshaft, a DTC sets. The distributor is repairable.

Camshaft Position Sensor


Object Number: 12799  Size: MH

The camshaft position (CMP) sensor is located within the distributor. The CMP operation is very similar to the crankshaft position (CKP) sensor, however the CMP provides one pulse per camshaft revolution (1X signal). This signal is not detrimental to the driveability of the vehicle. The VCM utilizes this signal in conjunction with the crankshaft position to determine which cylinders are misfiring.

Customer: replied 4 years ago.

Thanks Mark, we are in the same page here I was making sure we were. I went and bought a timing light after I posted my last question and used it and found that the timing mark on the harmonic balancer was to the left of the timing hump on the block, toward the passanger side of the truck. Does this mean the distributor needs to be rotated clock wise on the installation??

 

Also, I was just asking about the other codes to see if they were signifcant to this part of my problem.

Expert:  Mark replied 4 years ago.
Hello........


If the mark is to the left, that means your too advanced. I am not sure which way to turn it to be honest. Keep me informed and let me know how you make out.

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