Suburban miss fires after going up a hill?

[dwallace1234]

Originally Posted by suburban_lee

Cam Sensor Position Module?? Hmmm, sounds fancy. I referred to it as the Cam sensor. I assume we're talking about the same thing. Small part, about 2 by 1 inches, around $25 or so. If this doesn't answer your question, send me an e-mail.

Having problems sending u an email. But, the part sits on top of the distributor and has a three (3) pronged plug (female I believe). A picture of the part can be found at the following link: http://www.rockauto.com/ref/ACDelco/...ml?213-920.jpg.

Is this what you had changed?

Thanks.

[suburban_lee]

Yup, that's the part. After all it put me through, I thought about hanging it from the rear view mirror!

[dwallace1234]

Originally Posted by suburban_lee

Yup, that's the part. After all it put me through, I thought about hanging it from the rear view mirror!

Well, I had the "knock sensor" changed and it seems to have helped. I can pull my 27' StarCraft Travle Trailer (4,050lbs) up a small hill, and no misfiring, shaking or pinging. BTW, I also had a terrible time with pinging; sounded like a bunch of monkeys with ball peen(spelling??) hammers inside banging away.

Anyways, my mechanic has the camshaft sensor, but I am going to wait for a couple more days and see.

[99SUBGMC]

Well after reading all of the threads I changed the Cam Sensor Position Module this weekend and so far no shake rattle and roll when underload and shifting into overdrive. I will add this good luck lineing up the notch on the dist. plate.

[BigRedBurb]

I just discovered this forum, and this thread, so I guess I'll throw my hat into the ring as well.

We too have a '99 suburban with the 5.7. Bought the truck from a used car lot with 50K on the clock, so I don't know what was done before that, but it was pretty much a cream puff. We've had the truck about three years, and noticed the mis-firing problem pulling a camper on a trip out West the first summer we had it. First sign of trouble was a check-engine light that came on during a long easy hill at speed. Next day the light had gone off again, but it did this several more times. Finally on a really strenuous grade on I-70 in the Rockies, I got the blinking check-engine light and the shuddering. Slowing down cured the problem.

After arriving home, we continued to have problems even when not pulling a trailer. Exactly as the OP described, it would start shaking badly when cresting a hill. At first I thought it might have to do with what gear it was in, i.e. an RPM related problem. The local dealer checked the codes and detected a misfire (don't remember what cylinder), and a slipping transmission. They serviced and adjusted the tranny, and recommended I change out the cap, rotor, and plugs for the misfire. I did that, but didn't use GM parts. The problem continued. I had another dealership check it out: misfire diagnosis again. I replaced the cap, rotor, and plugs again using all GM parts this time, to eliminate that as a possibility. Since then we moved, and I haven't had it back to a dealer. The problem seemed to have lessened, but then where we live now doesn't require as much hiway driving. Recently we noticed the misfire problem is still there when nearing the top of a long hill.

Separately, we took the Burb in to an independent mechanic for what I thought was going to be a water pump, but turned out to be the intake manifold gasket. They also diagnosed a misfire, but I didn't ask them to check into it. The misfire is still there after the new gasket, same as it was before, so in this case they don't appear to be related. OTOH, perhaps whoever owned it before us already had the gasket replaced . . .

So after reading through this thread, the possibilities seem to be the cam sensor module, a sticky EGR, injectors, or carbon buildup in the intake. Is there any follow-up information that previous posters would care to add?

[mitch2264]

Oh great! Something else to look forward to with my '99 Suburban! I just had the intake manifold gasket replaced 2 weeks ago and I have noticed that it seems to be skipping at idle. We are suppose to drive it to the mountains at Thanksgiving so I guess I'll get to see if I am having the same problem everyone is describing with it missing at load going uphill. Let's see, it has 65,000 miles on it and so far I have had to replace the transmission at 60,000 miles to the tune of 2600.00. The old transmission was serviced per GM instruction. The intake manifold went out at 65,000 miles to the tune of 504.00. That is a bunch of coin!!

This is the nicest car I have ever owned from the heated leather seats to the self-dimming rear view mirror. It rides and drives great and the MPG is not bad for the size vehicle--actually got 19 on last trip. But if this thing keeps busting my chops I am going to have to unload it! I have an 88 Silverado with the old TBI 350 and it has 205,000 hard miles on it and none of the problems the Suburban has presented. It still has the original engine and transmission.

[GMMerlin]

I have to laugh at this thread...I have posted the fix for this concern many times here in the forum and it appears that no one has bothered doing a search to find the answer.

Misfires on these engines that occur under load (climbing hills or cruising at highway speeds) are usually caused by the valves sticking in the guides (after proper diagnosis of the fuel and ignition system rules out fuel or spark).
The cause is carbon buildup on the valve stems that cause the valves to stick in the guides under higher RPM (acts like valve float)
There are a couple paths to follow here.
You can use a product such as Seafoam in the oil and gas to help with lubercation of the valve stems.
Decarbonizing of your engine with GM Top engine cleaner will help.
Or if one of those 2 don't work the next thing is to remove the heads and have them professionally cleaned and the guides replaced.

[suburban_lee]

Laugh all you want, assuming that each and every problem with a similar sympton has the same cause is narrow minded. There are many causes that could contribute to a misfire condition, from as simple as bad ignition wires to your carbon-sticky valve issue. Truth is, it may not be a valve problem (something that we explored while diagnosing my same issue).

In your case, it was sticky valves, in my case it happened to be the CAM position sensor. How about we just pass the information and let those searching for it make the decision as to what to fix?

[BigRedBurb]

I know I'll be starting with the cheapest solution, then working my way up

[GMMerlin]

Originally Posted by suburban_lee

Laugh all you want, assuming that each and every problem with a similar sympton has the same cause is narrow minded. There are many causes that could contribute to a misfire condition, from as simple as bad ignition wires to your carbon-sticky valve issue. Truth is, it may not be a valve problem (something that we explored while diagnosing my same issue).

In your case, it was sticky valves, in my case it happened to be the CAM position sensor. How about we just pass the information and let those searching for it make the decision as to what to fix?

Once again someone reads half of what is written and jumps to a conclusion.
Go back and read ALL of my post..including this part
“Misfires on these engines that occur under load (climbing hills or cruising at highway speeds) are usually caused by the valves sticking in the guides (after proper diagnosis of the fuel and ignition system rules out fuel or spark).”
How can this be an “assumption that each and every problem with a similar sympton has the same cause”.
After ruling out the obvious (fuel and spark), an often overlooked area is the valvetrain, especially on these engines.
I personally have never seen a CMP sensor on these vehicle cause a misfire at highway speeds.
Usually any concerns related to the CMP sensor that I have seen revolve around worn Dist housing bushings or worn Dist driven gears.

The VCM uses the CMP 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.
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 .

So where your misfire and change in engine performance comes from is the change from a individual injector firing strategy to an all fire injector strategy.

[hugo11]

Guys,

I don't have the technicals knowledge on car engines but I was a mecanic on jets for 6 years.
What I learned was mostly that carbone deposit can be removed with the good chimical.
I've been struggling with my GMC Yukon for 6 months and spent $700 trying to fix all of the above.
Tired of the bad advices I decided to buy a quarter of SEA FOAM (2 bottles of 433 cl) at Autozone for $13.
Engine running with a gas tank almost dryed ( 2 gallons remaining) I poored the 2 bottles in my tank.
After 15 minutes at iddle speed my engine caughed and stoped.
Then I poored 5 gallons of fresh gas and crancked the baby.
After 10 second of caughing black smoke, my V8 sounded like a brand new one.
Some will tell me that there is a risk of destroying my fuel pump with that much SEA FOAM concentrated in only 2 gallons of fuel.
Maybe, but it worked better than anything I did before and cost only 13 bucks without destrying anything.
I dont say it will work for you but it worked for me

[Revenelson]

I had a similar problem, this might be another solution. But it is an expensive one!
The Problem:
99 Suburban Big Block- purchased with 59,000 miles and driven 500 miles no problems. First towing trip, towing a car trailer, first long steep hill, it feels like the transmission is slipping or someone unplugged 5 spark plug wires. Check engine light is on. After turning off the motor and turning it back on, it seems fine. Next hill same problem. Good news- it is under a used vehicle warranty. Bad news- when I took it to the dealer, since the check engine light was not on, they could not diagnose.
The Solution:
Long story short, I couldn't duplicate it except to hook up the trailer and tow up a long steep hill. I then drove to the dealer, with very little power, and did not turn it off. They connected their scanner- here's where my memory goes fuzzy- and they adjust some things. No change. He disconnects the connector (electrical) on the Mass Airflow Sensor and likes what he sees.
What Filter do you use?
He asks a question that surprised me.. Did I use a K&N Filter? The oil from those causes problems with the MAS. In my case no. They replaced the MAS and I have had no problems since.
Now I know why the original owner traded it in!!
The symptoms I had don't sound exactly like some who have posted here, but they do a little. Sorry I wasn't real detailed on the dealer troubleshooting. That was two years ago.

[99redsub]

I have had the same misfiring problems on my 99 Chevy Suburban (143,000 Km). Everytime I went up a hill and the rpm's were sustained between 2500 and 3000, the engine would noticably misfire and the codes consistently reported it was cylinder #6. I have replaced sparkplugs/wires, distributor, #6 fuel injector, flushed the engine to unstick valves, and I still experienced misfiring and codes. Finally, I pulled the pre-cat O2 sensor and took my burb for several test drives up and down some steep hills. No misfiring and no codes! I had a bad cat converter. Temporarily pulling the O2 sensor and taking a test drive might be a useful step in the process of helping to diagnose other engine misfiring problems. I wish I had done this before replacing the injector.

[audiosick]

After reading this thread and one titled "99 suburban wont start" I realized that the problems are fairly similar and require aproximatley the same repair. My 99 suburban wouldnt start one day and the next it did. I found this thread very informative and wanted to let anyone with these same issues know that after only one year of just having a complete tune-up I took my suburban (that wouldnt start) to the mechanic only for them to tell me that I needed yet another $424 tune-up! Theres no way! Turnes out the spark plugs did not need to be replaced, nor did the distrubutor cap, nor the wires. BUT the rotor button was a little burnt up. After buying a new one, a Haynes Manual, replacing the cam sensor, and feeding it some sea foam, my suburban starts up without any hesiatation, purrs like a kitten, and seems to have a little more pep. This was my fix....so far, so good.

[bodie06]

Originally Posted by 99SUBGMC

Well after reading all of the threads I changed the Cam Sensor Position Module this weekend and so far no shake rattle and roll when underload and shifting into overdrive. I will add this good luck lineing up the notch on the dist. plate.

I am having similar probs in my 97 suburban 4x4 with 33's and the hyperdyne programmer installed-with k&n filter. All the way up to like a month ago I could pull my 30' boat up ridiculous hills with that little small block and have no probs reving up to 5k etc. Now Im fighting with the dreaded po300 code but only under a load . the truck will kick down at speed to 5k then shift to o/d after that "stumble" and codes if I stay in the throttle. I have to let off for about 15 sec for it to run right again. Replaced plugs, wires, cap, rotor, fuel filter, cam sensor, fuel pres test 55@idle 65@load. Ran injector test thru scan tool . The dealer said I had a clogged cat, but I took it to a exhaust shop and that wasn't the case--pissing me off considering I work on blower motors and outdrives all day but can't fix my little sm. block!