Suburban miss fires after going up a hill?

[beardencove]

Originally Posted by 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.

My 98 Suburban had all the symptoms, going up the hill miss when pulling a trailer. New original cap, wires, cam sensor & two mechanics both reported # 5 Miss. but no solution. Guess what. The seafoam guy had my answer. One can in the tank, one can in the oil, and one down the brake vacum line (actually did this twice) and up the hill we went with no knock and no miss. Thanks.

[eez chevy]

i have 97 tahoe 5.7,havin a problem goin up hill, feels like im losin power,petal to the floor ,but still,no power,does anyone know of problem

[bkrman34]

Hello all I have a 1998 GMC 1500 truck with the 5.7L engine. It has about 85,000 miles on it. I first noticed the misfire problem after we bought a travel trailer and pulled it up a pass to go camping. The light came on and it was a random misfire under load. I started with the tune up, plugs, wires, cap, roter. And I had an injection cleaning and new fuel filter. Well the problem was still there and it started doing it without the trailer at the top of a long hill we live on. Just as I would get to the top and start to let off the gas it would start shaking really bad but it would go away after taping the gas a few times.(not enought to make the light come on) Right before a camping trip last fall it did it again with the trailer on a slight incline on the freeway. We turned around and headed back to the shop. They thought maybe they would try the EGR valve and that did the trick! We pulled over a 5000 foot pass both ways and not a problem. Well a month ago (4 mo. after the EGR) it started missing again!!! So then I tried the seafoam in the pcv line but I'm not sure it got to all the cylinders? The pcv enters on the side of the intake so I'm not sure if its one big cavity under there or not. I also put the seafoam in the gas and I will put some in the oil today. The seafoam in the intake didn't do the trick so I might try the egr again, but I'm not sure why the egr would work for 4 months and then start missing again ? Poor quality EGR ?? I can't afford a new truck but this misfire thing is really pissing me off!! It takes the fun out of camping because I worry the whole time if we'll make it there. I did put a K&N filter in last year and I thought I read someone posted about it could foul up the Mass airflow sensor?? I just don't know what to do.

[indust70]

I have a 99 chevy k1500 truck it was doing the same thing on misfiring going uphill or under a load. We changed everything Injectors, wire, plugs.sensor..etc. over 2000.00 worth of parts STILL NOT FIXED.
I changed the fuel cap with a factory one perfect now!!!! 10.00 FUEL CAP Make sure factory though.
Thought I would share my fix.
Lisa

[h2012]

I'm having similar problems but for some reason the plug in cylinder four keeps fouling out. About every two weeks it will start to idle rough and the check engine light comes on after each cleaning. Any ideas as to why this keeps happening?

[billinstuart]

Same problem, misfiring, 5.7 vortec, 140k miles. Just installed NEW heads (old ones cracked), polished rough edges in heads, cleaned piston tops like new, NEW fuel injection with electronic injectors, plugs, wires, distributor cap, rotor (all Delco or better, no crap), new thrust bushing in distributor, new crank sensor. no codes, cam retard ok, ran with GM Tech 2 scanner, everything normal. Popping is now WORSE with everything in great shape. disconnected EGR, no help. Can't drive over 60 without serious popping/misfire. Ran on ignition scanner..trace on primary side was perfect. Fuel pressure 55+ lbs. Replaced new injector system with old poppet valve injection unit..no difference. Really frustrated. Cam sensor in distributor just tells brain which cycle crank sensor is reading..at 2500 rpm shouldn't make much difference in injector pattern. TPS? Looked ok on Tech2. O2's were banging away. Short/long term fuel trim were ok. Cleaned Mass airflow sensor, no vacuum leaks, no slop in timing chain, distributor gear like new.

Frustrated as hell. It really feels like ignition problem, but nothing apparent. It's a small block Chebby..ain't new stuff. Someone out there MUST have figgered this out..talk to me!

[billinstuart]

Just read the fuel cap post again..I have disconnected the evap cannister and run it,,no help. There IS a breather on the top of the cannister..pulled up the plactic cover and cleaned the leaves out. No difference. The evap pipe goes across the motor and is connected to the purge valve on the passenger side of the upper manifold. It then breathes into a pipe that sticks up under the throttle body. BTW, cleaned the throttle body and IAC passage. No help.

[Quickpatch]

I don't have time to read all the replys to see if this was solved. I had same problem with 99 5.7 vortec in Van. After a year of looking for a solution to no avail, I went to dealer and they diagnosed as worn distributor shaft bushing or distributor shaft gear can't remember which. That fixed it. It was not the tranny, fuel injectors, tune up, wires, torque converter,intake manifold gasket etc. that was suspected by other mechanics. Hope this helps someone because it drove me crazy. Dale

[BigNed]

Hello all ,I had the same problem you all do , first I replaced the cap ,rotor ,pluges ,platinum # 2 plugs ,coil and ignition module , still no good. Then I ran into a old mechanic and he told me to put Sea Foam in my gas tank and in my oil to. Advance Auto sell's it $6.97 a can . Well I did it and 2 tank fulls later no more miss fires , it;s the motor that is gumed up from the gas . BigNed

[markdpro]

I have come to believe that this is a sensor induced problem. It could be ice forming in the intake, seeded by carbon (soot) bits. Spraying or adding cleaner to the fuel/induction system seems to fix it.

I don't think its sticking valves or some mechanical gremlin.

It can be a bad sensor by itself but trying cleaner is cheap and a quick fix if it works.

[BigRedBurb]

Originally Posted by BigRedBurb

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 . . .

Update to my own post: The Sub now has 160K on it, and still runs like a dream except for the misfire problem. Amazingly, I still have not tried SeaFoam, though I intend to do so finally this weekend. Since the last post, I replaced the fuel filter, the CMP sensor in the distributor, the fuel pump (it failed), and both cats (one was dead/clogged). 02 sensors tested fine. I also had the transmission flushed and serviced, since it was due, and I wanted to check for any possibly related problems. There were none.

Just returned from a trip through the Ozarks and Appalachians, misfire problem is as bad as ever, and I wasn't towing anything. Seems as long as I keep it in 3rd and under 65mph, the problem goes away. I have high hopes for the SeaFoam, because if that doesn't do the trick the next step is tearing into the intake and heads......

I still want to know why this problem seems to affect the '99s. What changed?

[CalessaSSracer]

I replaced my Crank sensor, problem solved.

[Ho ace]

99 suburban here and same problem! 128,000 miles

Started doing this a couple of years ago when pulling the boat but got so it would missfire without pulling the boat but only when going up a hill. Premium fuel helped reduce the problem.

My mechanic cleaned the popet valves last week and my family took it on a road trip this weekend running regular unleaded. No missfires, no shakes but I am getting a knocking (rattling) sound when accelerating. I don't know whats going on but its back to the mechanic. $$$$.$$

Anyone ever come up with a solution to this? My mechanic and I suspect the problem is carbon buildup.

[elorenzo39]

P0305 code on a 99 suburban.

I have the same problem with my Suburban. SVS Engine soon goes on when going on a uphill. Changed all plugs and wires. I was told to change the coil by another mechanic. Can you tll me with your experiences what did you do to fix the problem. Truck is well maintained but running out of ideas. I reside in Escondido. Please email me if you have an idea or remedy to the problem I am having. It would be greatly appreciate it.

Thanks...

[maxwedge]

Welcome to AF, this also can be caused by carbon deposits on the valve stems causing the valves to hang up in the guides, GM has a TSB on this issue covering your year I believe, the problem is pinpointing this as the issue, a top engine decarbonizing treatment is performed and if the condition clears up this indicates that is the problem, but this is a temp. repair, the heads would have to come off.