| From | Message |
Jack
Dodge Dakota
9/22/2001
00:13:29
|
 Subject: 87 V6 needs help - 1 cyl. not firing
IP: Logged
Message:
Hello Dakota heads, this is my first time posting here. I was hoping that maybe someone here might be able to give me some insight as to what might be ailing my 87 Dakota 3.9L V6. I posted to the CarTalk site and although I got a ton of response no one was able to suggest anything that helped. Below is a summary of the problem that I posted there. Do you think you could take a couple of minutes to read it and see what you think?? It's kind of long. I have been stumped so far. The last thing I did was check the timing and I adjusted it per the Haynes manual but that did not help. All cylinders check out between 120 and 140 on a compression test. I tried to buy a vacuum gauge, but none was to be found at four local auto parts stores. That may give me a hint as to the condition of the valves. I did a valve job about 5000 miles ago. It started up on the first try after that and has been running great ever
since....until now. It has less than 90K on the odometer. I am the original owner.
I lifted the valve cover on the non-firing cylinder side and everything seems okay. I watched the action while running the engine and nothing seemed broken. Thanks for any insight you might have. The only thing that I can think of at this point is the Spark Control Computer. Below is the start of the note that I posted to CarTalk.
Jack Shoults
Berkeley CA
_________________________________________
Subject: One cylinder not firing on 87 Dakota V6
ORIGINAL NOTE: Can anyone help with some ideas on this? I have one cylinder that is not firing. The wires are all new and the plug in that cylinder is new and I am getting spark out of the wire for that cylinder. The compression for that cylinder
reads 120. This non-firing cylinder problem began about 3 or 4 days ago and appeared to be intermittent. I first suspected the wires and changed those yesterday. The problem went away, but re-appeared today. I traced it to one cylinder, but as I mentioned, there is spark in the wire for that cylinder.
UPDATE: The latest on this is: 1. Wires are hooked up correctly. 2. There is bright blue spark at the plug when it is out of the cylinder. 3.Compression is 120 to 140 on all cylinders, including the non-firing cylinder.
I am resigned to removeing the valve cover in order to check the action on the intake valve. This is not a bigdeal, not like removing the intake manifold or the heads, but I expected that this was an electrical problem, but now I am convinced that it must be mechanical. A blockage in the intake port for that cylinder does not seem likely to me. The only thing that I can figure is that the intake valve is not opening when it
should.
There must be a problem with the lobe on the camshaft for that valve or the pushrod, rocker arm or the valve stem...anything in the mechanical assembly between the camshaft and the valve head.
The manner in which the problem manifested itself must indicate something. At first, there was obvious missing at idle and acceleration which disappeared at higher rpm and cruising. The first thing I checked was the connection of the plug
wires at the plugs and the distributor. I pushed each wire onto its connection point. Immediately after I did this, the engine ran even rougher. Aha, I thought, the wires are going and I furthered their demise by pushing on them. I bought some new ones and installed them. The engine ran smoothly after that. Problem solved, I thought. Anyone would have thought the same. But the next day, the missing started again. Well, I thought, it must be a bad plug, so I traced down which cylinder was missing by pulling each plug wire in turn until the engine ran the same with that particular wire disconnected. By this time, the missing was no longer intermittent, but very
ever-present at all speeds and temps. Only 3 or 4 days had passed since the onset of the problem.
At this point, I noticed one interesting characteristic. The engine runs better when the
plug to the suspect cylinder is disconnected than when it is connected. At first, I thought that I must have swapped a couple of wires as has been suggested here. I have checked and double checked and triple checked and quad and quint and sext
and sept. The wires are correctly hooked up.
The above mentioned characteristic WOULD seem to indicate swapped wires if the spark was coming on the upstroke of the compression cycle causing the mixture to explode against a still rising piston. I could see this scenario if the other swapped
wire was firing on the downstroke of the power cycle of the other piston. I am not familiar with the various positions of the pistons on a V6 engine so I cannot say off-hand if this scenario is possible, but having thought it through this far, I feel compelled to check the wires again.
(They're still hooked up right)
|
nate
Dodge Dakota
9/22/2001
02:24:01
|  I have an 88 with the same prob.
IP: Logged
Message:
My 88 (150k) will run like you said when I first start it in the morning and several minutes of driving later it will smooth out. I notice that it is especialy bad after it rains. My compression was good too. I also ran well at high RPM, but idled like crap. Does it ever back fire when appling the gas? Well, the problem i think delt with the distributor parts besides the cap and rotor. Give the whole thing a good look.
|
Jack
Dodge Dakota
9/22/2001
11:58:27
| RE: 87 V6 needs help - 1 cyl. not firing
IP: Logged
Message:
I'm going to yank the distributor today. I have a spare good pickup laying around from when I thought that had gone out for the second time (I was mistaken). The original pick-up did fail once and was causing the engine to stall at any time. I would have to wait about 15-20 minutes and it would start up again and run until the next stall which could be the same day or 3 days later, but that's another story. Sufice to say that I changed every other ignition component first .
I don't get any backfiring.
How long has your 88 been running like that? My problem started only 4 or 5 days ago and peaked two days ago. My problem started out like yours, but now it has evolved to being permanent. That is, it misses at all speeds, load conditions and temperatures and it appears to be missing only in one cylinder.
It just seems like the cylinder in question actually fires while the piston is still rising on the compression stroke because it runs better without that cylinder's plug hooked to the distributor. The plug DOES spark, but the engine runs better if I disconnect it. It runs fine on five cylinders, with the obvious loss in power and stuttering engine. If I hook up the plug in the wanky cylinder, I can barely get down the street. This sounds so much like swapped wires, but the wires are absolutely hooked up right. I'm beginning to suspect the Spark Control Computer. I'm going to try to unhooking the battery to see what happens when the computer resets itself. I'll try that, then I'll try changing the pick-up. If that's not it, I will take out the distributor and inspect the gears.
|
Jack
Dodge Dakota
9/22/2001
14:52:58
| Problem sovled
IP: Logged
Message:
nate,
I just changed the cap and rotor and that fixed it. Bohdan Bodnar on the rec.autos.tech newsgroup had this to say:
"An interesting problem, Jack. The observation that the engine appears to run better with the ignition wire disconnected makes even more interesting. I'm going to make a wild guess: high voltage leakage between ignition wires (the wires could be OK -- it could be carbon tracking in the distributor cap)."
Jack
|
Jack
Dodge Dakota
9/22/2001
14:54:01
| Problem sovled
IP: Logged
Message:
nate,
I just changed the cap and rotor and that fixed it. Bohdan Bodnar on the rec.autos.tech newsgroup had this to say:
"An interesting problem, Jack. The observation that the engine appears to run better with the ignition wire disconnected makes even more interesting. I'm going to make a wild guess: high voltage leakage between ignition wires (the wires could be OK -- it could be carbon tracking in the distributor cap)."
Jack
|
Donald
Dodge Dakota
9/22/2001
19:03:30
|  RE: 87 V6 needs help - 1 cyl. not firing
IP: Logged
Message:
I was just going to post a huge list of things. I'm gladyou got it fixed...
I had to replace the cap and rotor about 2 years ago. It wouldnh't even get out of the driveway.. Only 4 of the cylinders were firing...
ABout rough idling... : I talked toa mechanic about a year ago at a dodge dealership and he siad that the 87 dak engine is the roughest running engine he had ever seen, but if they are taken care of, they will last years and years...
I bought a new system computer, changed the Oxygen sensor, and put ona jacobs ignition system. It cost me about 600 dollars in all, but now my dak is the smoothest running 87 the mechanic ever saw. I did all the work trying to get rid of the annoying stalling problem, which it has almost completely taken away... just a slight stall when it is cold.. do you have any stalling or hesitation problem?
Donald
|
Jack
Dodge Dakota
9/22/2001
19:19:42
| RE: 87 V6 needs help - 1 cyl. not firing
IP: Logged
Message:
Hi Donald, the only stalling problem I ever had was solved by changing the Hall pick-up, but that was only after changing everything else didn't work. I was a severe pain in the butt and I was glad when it was over.
I think I have a very slight hesitation problem that is probably caused by the bands on the auto tranny needing to be adjusted. I'm sure it is not ignition related.
Jack
Now I can get on with what I was doing when the problem first surfaced, buying some new speakers for the stereo .
|
Donald
Dodge Dakota
9/22/2001
19:36:24
| RE: 87 V6 needs help - 1 cyl. not firing
IP: Logged
Message:
What is the Hall pick up?
Donald
|
Jack
Dodge Dakota
9/22/2001
23:40:26
| What is the Hall pick up?
IP: Logged
Message:
Sorry, it's more correctly called the Hall Effect pick-up. You can read about the theory of it here:
http://www.micronas.com/products/overview/sensors/index.php
I believe it replaces points in that it sends a signal to the computer telling it when to shut off voltage to the coil causing the magnetic field around the coil to collapse and that sends a high voltage jolt to the distributor throught the rotor to the appropriate wire and on to the plug. I think that's it...or something close. In the carbureted 87 V6 that I have, the Hall Effect pick-up is located beneath the rotor in the distributor.
Jack
|
Yurson
Dodge Dakota
JOIN HERE
1/06/2005
08:04:02
| 1987 3.9 v6 firing order
IP: Logged
Message:
I have 87 dakota and I am needing the firing order.Could you please give it to me. Thanx J.Bearden
|
Jack
Dodge Dakota
JOIN HERE
1/06/2005
11:25:59
|  RE: 87 V6 needs help - 1 cyl. not firing
IP: Logged
Message:
Facing the the engine from the front, this is the numbering of the cylinders.
6--5
4--3
2--1
The firing order is 1-6-5-4-3-2.
This is from the Haynes manual.
Good luck,
Jack
|
| | P 1 |
|
Post a reply to this message:
Username Registration: Optional
All visitors are allowed to post messages
|
