Question-------------------------Thank you for your input. My 1996 Grand Caravan has a 3.3L V6 engine with a 4 speed automatic transmission. The shop has checked the computer and replaced it to make sure it was ok. They also replaced the cam sensor and crank sensor.Before all these items were done the mechanic said that the van was firing on only 2 cylinders, and it is still only firing on cylinders. What are all the different items that could fail to cause the cylinders not to spark? I know this is a general question, but I am hoping to make sure we have exhausted all possible avenues. Is it possible that the coil could cause all this trouble? Thank you again for your prompt response earlier.
Followup To
Question -
Mr. Finston,
Thank you for your time. My 1996 Dodge Grand Caravan stalled at a stop sign and would not restart. It did not exhibit any difficulty until that time. Now the garage tells me that it is only getting spark on two cylinders. They have tried replacing the sensors to the cam and ? as well as the flywheel. (They were told that they could crack or warp and prevent firing.) It has been three weeks and they are still stumped. Now they are checking the wiring for continuity and charge. This has become very frustrating for myself as well as the garage. Do you have any insight as to what might cause a vehicle to stop and not restart in that manner? Is there something that they may not have checked? Also, I don't know if the spark plugs have been checked or changed for some time, could it be as simple as that?
Answer -
Hi Gary,
I just thought that if you have the 4 cyl. engine then it has a two part coil, just like the 3 part coils I described, and the checks are identical for it, except that it has the 3 pin plug, the center pin of which is the 12V B+ input pin. If you have the 3.0 V-6, this wouldn't apply because it has a distributor and a single section spark coil, whose resistance should also be checked, though it would not likely produce spark on only 2 cylinders, it would be more likely all or nothing. One tricky thing about that distributor is that the spark plug leads on the cap are not arranged in the same manner as the firing order, so if someone pulled all the wires and didn't notice that then the spark wouldn't be occuring at the right point in time but there would still be spark at all 6 plugs. This is a fine point whichprobably doesn't apply to your situation but I just mention it.
The last thing to test is whether the computer is actually sending the spark signal to the coil(s). Take a 12V test light and put one end on the + post of the battery, and then in turn touch the other end of the testor to each of the coil plug pins OTHER than the B+ pin (which I earlier mistakenly called the 12V pin) while a helper cranks the engine. The test light should pulse on and off rapidly for each of the three non-B+ wires at the plug (6 cyl) or each of the outside wires of the plug (4 cyl) so as to verify that the signal from the crank and cam sensor is actually being sent to the coils (i.e. it grounds those pins momentarily to create the spark). If not, and the sensors were installed properly and wired properly and you have no fault codes for the sensors then one would suspect the computer itself has gone bad.
Roland
AnswerHi Garry,,
Yesterday I sent you two answers, did you get the first one about the possibility that the spark coil is bad? That one essentially noted that because you have a direct ignition system (DIS) there is no distributor but rather the data from the crank and cam sensors is used by the engine computer to send spark timing signals to each of three separate coils (each coil fires 2 spark plugs simultaneously).
So on that basis, the fact that you only have 2 plugs showing spark makes me suspicious that your spark coil package has gone bad on two of its three parts. I gave resistance measurement for the primary and secondary winding of those coils (0.45-0.65 ohms and 7,000 to 15,800 ohms, respectively) which the shop can use to evaluate the condition of the three separate coils to see if two of them appear to be bad.
If they all read good, then the other possibility is that the signals are not being received at the plug-in to the coil pack. And my second reply (that you did 'copy' in this present question to me) speaks of how they could verify whether or not each of the three signals was getting to the input plug of the three separate coils. If they were not, then the only other possibility, since the computer was replaced, is that the electical wires from the sensors to the computer or from the computer to the coil pack are damaged, which they can verify by pulling the plugs and checking the wires. I can give you wire color codes if they don't have them.
But my first priority would be to see if the three coil sections in the pack behave electrically (ohms) identically to oneanother and meet the resistance values I listed above. If not, then based on that and the appearance of spark at only two plugs,I would say that you have a pretty firm indication that the coil pack has gone bad. Also the plugs that each section controls are paire for cylinders 1-4, 2-5, and 3-6 so the two cylinder/plugs that are working should be one of those three possibilities if my theory is correct.
I'm sorry if you didn't get the first part of my two part answer. With this response and the one you did get I think you can go to the shop and discuss this with them.
Let me know if you need anyother information, Garry, and also tell me what transpires with the repair process. I know you will get it fixed!
Roland
P.S. A basic question that you raised, why would an engine be only "firing on two cylinders" can be interpreted two ways: I have chosen to believe that what he meant was that spark necessary to cause firing was only being received by 2 cylinders (and that is how I based my answer above). He also could have meant that spark is arriving at all 6 cylinders but only two are detonating, and that would imply a different problem/answer: either the timing of the spark relative to the pistons is off (but that is hard to cause with the type of cam and crank sensor system you have there)or there is something wrong with the valves or the cylinders themselves on 4 of the 6. But that could be tested by a compression test on the cylinders. So either way you interpret his diagnosis, there is a pathway to a solution.
