Engine lopes for 3 minutes after cold start--head gasket leak???
From : daniel j stern
Q: on sat 12 jun 2004 jack wrote 1987 dodge dakota v6 carbureted 101k miles a *lot* of 87 carbureted 3.9 litre dakotas showing up in these groups over the last few weeks! i just finished some extensive maintenance including *installing expertly remanufactured carb more info. who expertly remanufactured it there is no such thing as expert remanufacturing. remanufacturing is a process by which carburetors starters alternators etc. are stripped down component parts thrown in bins and brutally cleaned en masse then reassembled on an assembly line by semi-skilled drones who just use whatever component part comes down the line. finished units are overly consolidated many *different* original units consolidated into one item that doesnt work correctly in any of the numerous applications for which it is claimed to be the correct replacement and usually are considerably inferior to original or expertly ***rebuilt*** units. *new plugs wires cap rotor and coil not sure why a coil was on the list...they dont usually go bad. but replacing the secondary side of the ignition is a good periodic maintenance procedure. *checking all vacuum lines for air-tightness also good. i do not see an oxygen sensor on your list of recent maintenance nor do i see anything about the crankcase ventillation system pcv valve crankcase inlet air cleaner/oil separator unit and all hoses. white smoke gulp has been spotted rising gently in the air from the rearview mirror. this all lasts only for 2 or 3 minutes and then it runs perfectly. are you quite sure its white *smoke* and not steam what does it smell like i have a vacuum gauge hooked up in the cab so i can monitor it as i drive. at warm idle with auto trans in gear vacuum is a steady 18 lbs. at warm idle with trans in neutral vacuum is a steady 20 lbs. curb idle rpm is factory spec 700. fine...fine... after driving about 200 miles since this started coolant level is at the low marker in the reservoir. i am not sure at what level the coolant was when the problem started. fill it back up to max and keep an eye on it. i suspect an early stage blown head gasket. possibly or an internal non-gasket leak. note that if you are indeed burning coolant your o2 sensor is burnt toast one plus is that there is no evidence of water in the oil. thats a good thing. pull the plugs back out and see if one of them looks markedly different from the others. i thought that perhaps the symptoms were pointing to a leak in the head gasket that is causing misfiring and the leak gets closed as the engine warms up. does not usually happen with *gasket* leaks but can happen with internal engine leaks. if a leaking head gasket turns out to be the problem i plan to try crc copper block weld or similar product before tearing out the heads. this is a very poor idea. all it will do is cause additional problems radiator and heater core plugging. -stern .
Replies:
From : daniel j stern
on sat 12 jun 2004 jack wrote *the rebuilder did an excellent job on this carb. ah ok so there was a singular individual rebuilder. thats an expertly *rebuilt* carburetor not remanufactured. *i could not get out to give the white smoke a sniff. the engine would die. thats pretty serious and more than just a lope. the o2 sensor appears to be operating correctly. i am using a digital meter to monitor the duty cycle of the solenoid. the reading hovers around 50% when cruising just as it should. if the o2 sensor dies from coolant in the exhaust it should show up as an abnormally low duty cycle reading contamination frequently causes the o2s to get lazy/slow rather than die completely. dont think thats causing your poor cold running just making that note for you. can a sticking valve cause the symptoms that i described loping at startup after complete cool down and then running fine after 3 minutes of warmup yes but this symptomology is very seldom caused by a stuck valve with todays fuels and oils and that would not explain your white smoke. i dont like the idea of the cooling system sealant either. but i also dont like the idea of pulling the heads - sealant will not fix the problem; you will have to fix it i.e. pull the heads anyway *and* youll have a major cleanup job and probable core/radiator replacement if you put in sealant. .
From : jack
*half of those 87 dakotas you mentioned was probably mine. *the rebuilder did an excellent job on this carb. i know quality when i see it. no play in the throttle shaft plates fit the bore nicely and when fully closed they were in exactly the correct relation to the idle transfer slot. i rebuild the mixture control solenoid myself as i would not trust that to anyone. *coil was replaced because the spark it produced was a weak yellow. curb idle rpms rose by 250 after replacement. i had to reset idle mixture screws and idle speed screw. needless to say i was very pleased. *i could not get out to give the white smoke a sniff. the engine would die. *new o2 sensor and pcv valve were installed. i forgot to note that. egr valve was operating correctly so i left it in. the o2 sensor appears to be operating correctly. i am using a digital meter to monitor the duty cycle of the solenoid. the reading hovers around 50% when cruising just as it should. if the o2 sensor dies from coolant in the exhaust it should show up as an abnormally low duty cycle reading as the system tries to react to what it perceives as a too lean mixture caused by a non-existant o2 sensor voltage. perhaps the leak whether head gasket or internal engine is not to the water jacket but simply to the atmosphere. i will check the plugs in the morning. when each one is out i plan to also check for water in the cylinder and do a compression test. can a sticking valve cause the symptoms that i described loping at startup after complete cool down and then running fine after 3 minutes of warmup i dont like the idea of the cooling system sealant either. but i also dont like the idea of pulling the heads - jack daniel j. stern wrote on sat 12 jun 2004 jack wrote 1987 dodge dakota v6 carbureted 101k miles a *lot* of 87 carbureted 3.9 litre dakotas showing up in these groups over the last few weeks! i just finished some extensive maintenance including *installing expertly remanufactured carb more info. who expertly remanufactured it there is no such thing as expert remanufacturing. remanufacturing is a process by which carburetors starters alternators etc. are stripped down component parts thrown in bins and brutally cleaned en masse then reassembled on an assembly line by semi-skilled drones who just use whatever component part comes down the line. finished units are overly consolidated many *different* original units consolidated into one item that doesnt work correctly in any of the numerous applications for which it is claimed to be the correct replacement and usually are considerably inferior to original or expertly ***rebuilt*** units. *new plugs wires cap rotor and coil not sure why a coil was on the list...they dont usually go bad. but replacing the secondary side of the ignition is a good periodic maintenance procedure. *checking all vacuum lines for air-tightness also good. i do not see an oxygen sensor on your list of recent maintenance nor do i see anything about the crankcase ventillation system pcv valve crankcase inlet air cleaner/oil separator unit and all hoses. white smoke gulp has been spotted rising gently in the air from the rearview mirror. this all lasts only for 2 or 3 minutes and then it runs perfectly. are you quite sure its white *smoke* and not steam what does it smell like i have a vacuum gauge hooked up in the cab so i can monitor it as i drive. at warm idle with auto trans in gear vacuum is a steady 18 lbs. at warm idle with trans in neutral vacuum is a steady 20 lbs. curb idle rpm is factory spec 700. fine...fine... after driving about 200 miles since this started coolant level is at the low marker in the reservoir. i am not sure at what level the coolant was when the problem started. fill it back up to max and keep an eye on it. i suspect an early stage blown head gasket. possibly or an internal non-gasket leak. note that if you are indeed burning coolant your o2 sensor is burnt toast one plus is that there is no evidence of water in the oil. thats a good thing. pull the plugs back out and see if one of them looks markedly different from the others. i thought that perhaps the symptoms were pointing to a leak in the head gasket that is causing misfiring and the leak gets closed as the engine warms up. does not usually happen with *gasket* leaks but can happen with internal engine leaks. if a leaking head gasket turns out to be the problem i plan to try crc copper block weld or similar product before tearing out the heads. this is a very poor idea. all it will do is cause additional problems radiator and heater core plugging. -stern .
From : daniel j stern
on sat 12 jun 2004 jack wrote i will assume that the white smoke i am seeing at startup is just normal moisture accumulation well here again -- you need to check if its smoke or steam. hmmm... the only ignition part that i didnt change was the resistor. i wonder if that could be it. no. i have been doing web and group searches and the one piece that i found describes a problem that is closest to mine is the one i cut and pasted below. the bmw problem the article describes has zero relevance to your truck. -stern .
From : jack
thanks for all the intelligent feedback. it is helping me in that process of eliminating what it aint. as it stands now i am going to try living with the condition for a while until i get a clearer idea of what is actually causing it. i will just have to let it warm up for the 3 minutes that it takes for the problem to disappear... and it disappears immediatley. one second the engine feels like it is running on 4 or 5 cylinders the next second all 6 are firing and its all systems go. i will assume that the white smoke i am seeing at startup is just normal moisture accumulation in connection with the misfiring until something proves otherwise i.e. lowering of coolant level or white smoke present after warmup. i dont want to get sidetracked into thinking it must be the head gasket. its just that i am nervous about that. one of the head gaskets blew about 35000 miles ago and i fixed it myself. i wouldnt mind so much if i had just spent that last two months at the beach but i have been working on this truck on weekends and evenings while doing contruction for about that same amount of time. hmmm... the only ignition part that i didnt change was the resistor. i wonder if that could be it. i would much rather deal with an ignition problem than a leaking cylinder. i have been doing web and group searches and the one piece that i found describes a problem that is closest to mine is the one i cut and pasted below. thanks again for the response time. jack http//member.rivernet.com.au/btaylor/bmwtext/technical/idlelopewarmuponly.html idle lopes during warmup only date thu 06 may 1999 from chao harvey harvey.chao@lmco.com subject e28 2.7 l lopes on warmup - followup several weeks ago i requested suggestions regarding the way my 2.5 m20 idle lopes during warm up - between the time the temp. gauge needle is between the edge of the blue zone and fully warm. it was almost like a bad idle control valve except that 1 when the engine warmed up i had a nice steady idle 2 it is a new icv 3 if i adjusted the screw on the icv i could get the lope to go away but then the icv drew excessive current. one of you suggested a bad fuel pressure regulator only response. i thought about the behavior and in particular about the fact that adjusting the icv bleed screw i think to allow more air seemed to make the problem go away but draws excessive current which could cause premature failure of the output transistor in the icu which drives the icv. so i began to think about maybe when properly set up not enough air was getting past the throttle butterfly so the icu/icv increase bypass airflow and overshoots and then undershoots causing the loping idle. my understanding is that the butterfly is set to a very fine tolerance just slightly open at idle the theory that evolved is that when the engine is warm the butterfly housing expands from the heat enough to increase the opening between the throat and butterfly valve allowing just enough air with proper icu/icv operation to idle properly. so - this past weekend i used some spray carb. cleaner to clean the butterfly valve and its throat - and the lope is gone! no other adjustment or action taken just used a spray can of carb. cleaner and cleaned out any residue from oil gas dirt etc on and around the throttle butterfly valve and its throat. ymmv harvey i live with fear death and evil...but sometimes i turn it off and use a mac. author unknown .
From : Annonymous
my shadetree diagnosis given your symptoms is a blown head gasket. pull all the plugs then run a compression check. if you go to the trouble to tear it down for heavens sake pull both heads and have the valves/seats done. prolly wouldnt hurt to spend a few more bux and replace the valve springs. of course with the top end all freshly tightened up and while the heads are off a ring job would prolly be a smart idea. of course that means pulling the pistons out which means it would also be a good time to replace the rod bearings and while were in there main bearings. ;- never ending. labor is the expensive part. if you have the tools and knowhow pull it down yourself then take the heads and block to an automotive machine shop and have them do the valves & seats rings & bearings. does anyone still lap-in the valves anymore *half of those 87 dakotas you mentioned was probably mine. *the rebuilder did an excellent job on this carb. i know quality when i see it. no play in the throttle shaft plates fit the bore nicely and when fully closed they were in exactly the correct relation to the idle transfer slot. i rebuild the mixture control solenoid myself as i would not trust that to anyone. *coil was replaced because the spark it produced was a weak yellow. curb idle rpms rose by 250 after replacement. i had to reset idle mixture screws and idle speed screw. needless to say i was very pleased. *i could not get out to give the white smoke a sniff. the engine would die. *new o2 sensor and pcv valve were installed. i forgot to note that. egr valve was operating correctly so i left it in. the o2 sensor appears to be operating correctly. i am using a digital meter to monitor the duty cycle of the solenoid. the reading hovers around 50% when cruising just as it should. if the o2 sensor dies from coolant in the exhaust it should show up as an abnormally low duty cycle reading as the system tries to react to what it perceives as a too lean mixture caused by a non-existant o2 sensor voltage. perhaps the leak whether head gasket or internal engine is not to the water jacket but simply to the atmosphere. i will check the plugs in the morning. when each one is out i plan to also check for water in the cylinder and do a compression test. can a sticking valve cause the symptoms that i described loping at startup after complete cool down and then running fine after 3 minutes of warmup i dont like the idea of the cooling system sealant either. but i also dont like the idea of pulling the heads - jack daniel j. stern wrote on sat 12 jun 2004 jack wrote 1987 dodge dakota v6 carbureted 101k miles a *lot* of 87 carbureted 3.9 litre dakotas showing up in these groups over the last few weeks! i just finished some extensive maintenance including *installing expertly remanufactured carb more info. who expertly remanufactured it there is no such thing as expert remanufacturing. remanufacturing is a process by which carburetors starters alternators etc. are stripped down component parts thrown in bins and brutally cleaned en masse then reassembled on an assembly line by semi-skilled drones who just use whatever component part comes down the line. finished units are overly consolidated many *different* original units consolidated into one item that doesnt work correctly in any of the numerous applications for which it is claimed to be the correct replacement and usually are considerably inferior to original or expertly ***rebuilt*** units. *new plugs wires cap rotor and coil not sure why a coil was on the list...they dont usually go bad. but replacing the secondary side of the ignition is a good periodic maintenance procedure. *checking all vacuum lines for air-tightness also good. i do not see an oxygen sensor on your list of recent maintenance nor do i see anything about the crankcase ventillation system pcv valve crankcase inlet air cleaner/oil separator unit and all hoses. white smoke gulp has been spotted rising gently in the air from the rearview mirror. this all lasts only for 2 or 3 minutes and then it runs perfectly. are you quite sure its white *smoke* and not steam what does it smell like i have a vacuum gauge hooked up in the cab so i can monitor it as i drive. at warm idle with auto trans in gear vacuum is a steady 18 lbs. at warm idle with trans in neutral vacuum is a steady 20 lbs. curb idle rpm is factory spec 700. fine...fine... after driving about 200 miles since this started coolant level is at the low marker in the reservoir. i am not sure at what level the coolant was when the problem started. fill it back up to max and keep an eye on it. i suspect an early stage blown head gasket. possibly or an internal non-gasket leak. note that if you are indeed burning coolant your o2 sensor is burnt toast one plus is that there is no evidence of water