High idle

[pappyam]

November 25 2010
Gmc Jimmy 4 door 4wd A/T.

This is to document all the steps taken to find the cause to a flashing MIL with misfire and no codes.

Fuel pressure was verified a few times over a period of a few hours. Results are:
key on engine off: 58 psi max. Tried cycling on and of but did not go any higher.
key on eng. run: 58 to 58 psi. Jerking the throttle open, pressure builds to approx. 64 psi.
key off engine off: after 5 min bleed time 55psi
after 10 min bleed time 52 after 30 min bleed time 48psi after 60 min bleed time 42psi
I realise that pressure is a few pounds below what it should be but, upon quick acceleration, it builds up to spec or very near so I don't think this is the cause of the misfire, or why the truck shakes and wants to die when put in gear,especially at idle which holds @ 1200rpm BTW.
Here is the link to a video I made to check fuel pressure:http://s1142.photobucket.com/albums/...t=100_0099.mp4

Checked the health of engine with vacuum gauge. 19"Hg @ 1200rpm idle. Needle very steady. Snapping the throttle brings it close to 0 and around 23 to 26 "Hg upon deceleration. Does not look like anything leaking or sticking or burnt valves or even ignition miss.Another link to video:http://s1142.photobucket.com/albums/n615/pappyam/?action=view&current=100_0099.mp4#!oZZ1QQcurrentZZ http%3A%2F%2Fs1142.photobucket.com%2Falbums%2Fn615 %2Fpappyam%2F%3Faction%3Dview%26current%3D100_0083 .mp4

Today, I performed a compression test that revealed cyl. #4 and 6 to be low (155psi) compared to others that are between 176 to 180psi. A second test with oil in the cyl. showed and improvement to 180 psi. Cyl. leak test confirmed that piston rings were at fault because air was coming out of the dipstick and leakage was around 25% on gauge. No air coming out of radiator or out of adjacent cyl so, no blown head gasket or cracked block. No air out of TB or tail pipe.
As stated earlier, this was suppose to be a new engine. Cosmetically, it did not show any signs of wear when I bought it although it had been sitting bolted to an engine stand in an unheated shed for the last 13 years. The PO took care to bathe it in oil. I was wondering if the rings could be stuck after sitting for so long!! I sure don't want to pull it out again. I poured about 4 ounces of a mix I made (30% PB blaster with 70% transmission oil) into each of the 2 low cyl. and will let it sit for a day or so to see if it helps. Anyone have another recipe to free stuck rings, if that is what it is? If someone has another idea of what the problem could be, I am interested in hearing it but, I am a little scared of how it looks right now.
Don

[82Stang]

I watched the video and saw the rough idle. If it were me on my blazer, I'd think two things with that idle;

1) vacuum leak, IAC(port in plenim get's clogged not allowing IAC to seal, IAC also must have oring around it to seal properly), EGR, fuel filter, stuck PCV valve. Everything in the vicinity of the upper plenim.

2) misfire=ignition usually. plugs, wires, coil(s), battery wires, check voltage output of alternator.

Of course, you may have already checked/done these. Or they may have nothing to do with your specific problem so take it for what it's worth. One more thing too. I've never been a fan of engine additives or crap like that, but maybe if you do have some stuck rings, an engine flush would work. Not sure if engine flush is worth doing or not, maybe someone else can weigh in on using that stuff. I'd think the tranny fluid would accomplish the same thing. But if I knew I had a stuck valve, I might try it.

Hope this helps.

[pappyam]

Thanks 82Stang
Well, I am really at a lost here. Zipped everything back together and started the truck. Real nice smoke show. The mixture I put in seems to have helped loosen 4 and 6 but, I still have that f*****g misfire. I narrowed it down to #3. Pull the wire and nothing changes. Idle's at 1000rpm now. Changed plugs this morning. Switched wiring from #5 to #3. Same thing. I have 178 psi in that cylinder and I know for a fact that the plug is firing. I have been at this for 1 month now and I need to get this on the road for next week. I don't know where to go from here. Please HELP!!!!
Don

[82Stang]

Here's a good read, maybe point you in the right direction...

http://www.aa1car.com/library/misfire.htm

It could be as simple as an EGR valve or valve seals. But then again, you never know...

Good luck.

[pappyam]

At this point, I think I might have a plugged injector. I guess there is no way to test or clean them without taking the intake apart. Today, it snowed so, this is making it kinda hard to work on the truck outside. I hope I find the problem soon because I am tired of putting $$ and time and it still is not working.
Don

[MT-2500]

Originally Posted by pappyam

At this point, I think I might have a plugged injector. I guess there is no way to test or clean them without taking the intake apart. Today, it snowed so, this is making it kinda hard to work on the truck outside. I hope I find the problem soon because I am tired of putting $$ and time and it still is not working.
Don

As to putting money in it and no fix proper testing will take care of that problem.
First confirm that you have the dist set to within - or + 1 or 2 degrees of of 0 degrees camshaft retard.
Also confirm good fuel pressure and good hot blue spark to missing cylinder.
A bad or dirty MAF sensor can also cause miss fire.
Check and make sure 02 sensors are working good.
Confirm good engine vacumn.
As to testing injectors yes there is a injector balance test in a good engine capable scanner that will test each injector.

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

[pappyam]

As explained above as far as fuel pressure this is what has been done but, since it is not plated yet, I can't take it on the road for a spin.

Fuel pressure was verified a few times over a period of a few hours. Results are:
key on engine off: 58 psi max. Tried cycling on and of but did not go any higher.
key on eng. run: 56 to 58 psi. Jerking the throttle open, pressure builds to approx. 64 psi.
key off engine off: after 5 min bleed time 55psi
after 10 min bleed time 52 after 30 min bleed time 48psi after 60 min bleed time 42psi
I realize that pressure is a few pounds below what it should be but, upon quick acceleration, it builds up to spec or very near so I don't think this is the cause of the misfire, or why the truck shakes and wants to die when put in gear,especially at idle which holds @ 1200rpm BTW.

I have located the misfire on cyl. #3 and it holds 178 psi pressure. I let it run with another spark plug in the #3 boot and there is a nice powerful spark. I starts easily hot or cold with no problem but I can feel the misfire as soon as I give it gas and of course, the MIL is flashing steady.As soon as I put it in gear, the truck shakes badly and you can really feel it under load.
I purchased a laptop and a cheap scanner (Elmscan5) but it does not give cam retard. On the other hand, the dist. has no means to move because the hold down bracket hole is only large enough to fit the bolt.
The vacuum holds steady @ 19psi.
I cleaned the MAF, IAC and EGR valves to the best of my knowledge. As for the O2 sensors, I presently have the wrong ones in and they are not connected. Could this cause a misfire always on the same cyl? I received the new ones yesterday and will be putting them in next. This misfire has been happening since day 1, when I started this new engine. I was not positive before that it was #3 but, now I am. That is why I was thinking of a plugged poppet I wanted this car for the winter but, it has to be plated by the end of the month and, I do not want to do so if it will not be reliable. So, after all that has been done, is it logical to think of a bad or plugged injector? I don't have the equipment to test it at home,short of taking the spider out and clean it.
Don.

[MT-2500]

Originally Posted by pappyam

As explained above as far as fuel pressure this is what has been done but, since it is not plated yet, I can't take it on the road for a spin.
I have located the misfire on cyl. #3 and it holds 178 psi pressure. I let it run with another spark plug in the #3 boot and there is a nice powerful spark. I starts easily hot or cold with no problem but I can feel the misfire as soon as I give it gas and of course, the MIL is flashing steady.As soon as I put it in gear, the truck shakes badly and you can really feel it under load.
I purchased a laptop and a cheap scanner (Elmscan5) but it does not give cam retard. On the other hand, the dist. has no means to move because the hold down bracket hole is only large enough to fit the bolt.
The vacuum holds steady @ 19psi.
I cleaned the MAF, IAC and EGR valves to the best of my knowledge. As for the O2 sensors, I presently have the wrong ones in and they are not connected. Could this cause a misfire always on the same cyl? I received the new ones yesterday and will be putting them in next. This misfire has been happening since day 1, when I started this new engine. I was not positive before that it was #3 but, now I am. That is why I was thinking of a plugged poppet I wanted this car for the winter but, it has to be plated by the end of the month and, I do not want to do so if it will not be reliable. So, after all that has been done, is it logical to think of a bad or plugged injector? I don't have the equipment to test it at home,short of taking the spider out and clean it.
Don.

On fuel pressure you have to have pressure up to specs for a injector to squirt on a cold start or cold.
Does the miss get better or stay the same cold or hot?
If you have good spark and compression and plug and fuel pressure and injector pulse to that cylinder and no vacumn leaks on it then go for a injector.
I have never had any luck cleaning them or poppet.
On you engine you can replace just one at a time.
before replacing injector I would check injector plug in wiring for locked in good and for injector pulse to that injector.

On 02 sensors causing engine miss I have had some problems with the 02 sensor wiring shorting out from corrision in it and knocking out no 4 injector.
That is a good reason to check for injector pulse to injector.
Good Luck and let us know how it goes.

[pappyam]

MT 2500
Compression, spark etc all good. As for misfire, there is no difference hot or cold.

That is a good reason to check for injector pulse to injector

Is that something a DIY mechanic can do at home and how is this done. I do have a fair assortment of tools if you explain how this is done.
Don

[MT-2500]

Originally Posted by pappyam

MT 2500
Compression, spark etc all good. As for misfire, there is no difference hot or cold.

Is that something a DIY mechanic can do at home and how is this done. I do have a fair assortment of tools if you explain how this is done.
Don

You can check injector pulse with a injector tester noid light.
Most parts places have them.

Find the two injector wires or pulse wire to the missing cylinder and hook the noid light to them or pulse.
Watch the light for a good steady blink.
If so you have good injector pulse.
Let us know how it goes.
Good Luck

[pappyam]

I was checking the pulse from the vcm with a noïd light in the injector module connector as suggested by MT2500, when I noticed the pin for #3 cyl. was bent. Straightened and wisfire disapeared. Now truck runs like a champ except for the idle issue. All that time and $$ for such a simple fix!! I went for a 50 mile ride yesterday to get it nice and hot. When I put it in gear, idle goes from 1100 rpm and jumps to between 1500 to 1800 rpm. The truck is acting like a thouroughbred and it does make it hard to keep on the line. I am sure it is something stupid and I am missing it. Like I mentioned in my first post, it ran good with the old motor. I can't find any vacum leaks. It could be like 82Stang mentioned, the Iac valve. But I don't want to throw anymore $$ on parts till I am sure that they are shot. BTW, I put in new O2's so that eliminates a potential problem. As far as computer controlled equipment, the only non original part is the cranck sensor. It was already attached to the timing cover of this engine.
I will take a ride with my scanner plugged in and report back my findings. Thanks everyone for your help. We found the misfire and I am positive that the idle issue will be settled shortly.
Don

[MT-2500]

Originally Posted by pappyam

I was checking the pulse from the vcm with a noïd light in the injector module connector as suggested by MT2500, when I noticed the pin for #3 cyl. was bent. Straightened and misfire disapeared. Now truck runs like a champ except for the idle issue. All that time and $$ for such a simple fix!! I went for a 50 mile ride yesterday to get it nice and hot. When I put it in gear, idle goes from 1100 rpm and jumps to between 1500 to 1800 rpm. The truck is acting like a thouroughbred and it does make it hard to keep on the line. I am sure it is something stupid and I am missing it. Like I mentioned in my first post, it ran good with the old motor. I can't find any vacum leaks. It could be like 82Stang mentioned, the Iac valve. But I don't want to throw anymore $$ on parts till I am sure that they are shot. BTW, I put in new O2's so that eliminates a potential problem. As far as computer controlled equipment, the only non original part is the cranck sensor. It was already attached to the timing cover of this engine.
I will take a ride with my scanner plugged in and report back my findings. Thanks everyone for your help. We found the misfire and I am positive that the idle issue will be settled shortly.
Don

Good find there pappyam

I have also found the injector plug-in on top of engine not plugged in good.
Always make sure it snaps down good.

On the idle control problem watch and check your tps voltage real close.
Let us know how it goes.
Good Luck

[pappyam]

I went for a ride with the scanner plugged in. I got code P0507 which is related to the IAC I believe. I don't know if this is relevant but, I remembered that when I cleaned the IAC,I plugged it in whitout installing it. By the time I got to turn the key on and get back under the hood to see if anything would happen, the pintle and spring had already flown inside the engine compartment. I found the parts and reassembled the valve but, it was difficult to put it back in. Is it possible that upon reassembly, the toothed shaft would not be sitting at the original place? The computer would activate the pintle but, it would not be where it should be or, would the computer adjust it where it should go anyway?
Don

[MT-2500]

Originally Posted by pappyam

I went for a ride with the scanner plugged in. I got code P0507 which is related to the IAC I believe. I don't know if this is relevant but, I remembered that when I cleaned the IAC,I plugged it in whitout installing it. By the time I got to turn the key on and get back under the hood to see if anything would happen, the pintle and spring had already flown inside the engine compartment. I found the parts and reassembled the valve but, it was difficult to put it back in. Is it possible that upon reassembly, the toothed shaft would not be sitting at the original place? The computer would activate the pintle but, it would not be where it should be or, would the computer adjust it where it should go anyway?
Don

You may have damaged it.

If the computer can adjust it and the IAC valve is working right yes it will go to the correct idle or where were it should.
Also clean throttle valve butterfly with carb cleaner and tooth brush.
And make sure return spring is closing butterfly good.

Does you scanner read iac counts and desire IAC valve counts?
If so they should match.
If not PCM has lost IAC valve control.
Bad PCM or IAC.

Does your scanner have a idle speed control/adjust test where you can control iac valve to different idle speed?

[pappyam]

I am by no means a mechanic, more of a tinkerer. So I have a small pc compatible scanner that is just slightly better than a code reader.
It was suggesteed on another forum that my throttle cabble might be to short and, I have to admit that I was thinking the same thing the first time I started the truck with the new engine. But this cable is not adjustable, not twisted in anyway. It is the same one that was on the truck before. I looked undeneat the dash and there is a small pellet on the cable that act's as a stopper. The throttle is approx. 3/16" from the throttle stop screw. If I disconnect the cable, the truck barely stays at idle (600 rpm). I was hesitant to remove it and try to bring the pellet up closer to the pedal since, it was OK on the former engine and I don't want to screw up the electronics. What do you guys think?