87 325 i spark out the coil won't run

#1

my brothers 87 325 i. he was driving it and he said he put in neutral rev it up there in the rpms and he made it to our older brothers house and it wouldnt never start back up.its getting fuel its getting spark out the coil wire,theres spark from the cap but its weak spark, no spark out the wires. new cap and rotor.new cps. new main relay. I was thinking plug wires but just want to make sure its not something else any help would be greatly appreciated so he can get off my back bout fixing his car.

#2

How do you know it’s getting fuel?

Describe “weak spark” with more detail.

I once had these exact same symptoms in a newly installed motor. The problem turned out to be the rotor. I hadn’t quite got it on square so it was tilted a little and making only partial contact with the conductors on the dist cap. The rotor being off-square was invisible. It was another guy that spotted the problem in that he noted that the abrasion pattern on the cap’s conductors, where the rotor sweeps by, wasn’t right and the rotor’s conductor was hitting as much plastic as it was dist cap conductor.

Check the electrical connector to the fuel injectors under the intake manifold. Reseat main relay. Remove, clean reinstall engine’s ground at oil pan.

Who knows, the engine could just be flooded. If you think it could be flooded, hold gas pedal down. DME will understand and quit pushing so much fuel.

#3

Its getting fuel to the rail the injectors a working properly. i will recheck the rotor.Its not getting any spark out the plugs,new plugs and coil. and the spark you can barley see spark coming out the dist. cap with a tester its not a clean white spark.

#4

I’m not sure that I can tell a good spark from a weak spark, but if you can I won’t dispute the idea. Lots of folks have more experience than I.

If the spark is weak that narrows it down an awful lot. I would take cable between dist cap and coil and remove it from the dist cap such that it only goes to the coil. Then run the starter and look at the spark between that cable end and ground. Pull back the rubber housing a little if that’s necessary in order to get spark. If the spark’s ok, then it’s the rotor or dist cap. If the spark’s not ok, then it’s the coil or the wire to the coil.

A word of caution. You seem to be having significant success observing the ignition spark. I gotta tell you tho, every single time I’ve done it, no matter what precautions I take, at some point of the process I get the shit zapped out of me.

There are spark plug tester doohickey’s that you stick in the plug wire and it lights up when it gets hit with voltage. I wonder how those react to a weak power surge.

#5

yea thats what i have is a spark tester you can watch the spark and kinda get a idea of a good spark and a weak one like i said its good coming out the coil and the coil wire it just gets weak on the dist. cap and no spark at the plug itself.

#6

Well, that sounds like you’ve got the problem pretty well narrowed down. Inspect rotor and dist cap carefully for anything odd…
–Black smudges near conductors.
–Odd abrasion patterns on rotor or dist cap conductors. This includes metal or plastic parts.
–Check rotor for cracks in the plastic due to over tightening of the rotor screws. Confirm that rotor is on square.
–Confirm that all plug wires are firmly seated in dist cap. Remove black plastic cover from dist cap if you have one. It’s easier to ensure that plug wires are all the way seated into dist cap with the black plastic dist cap removed.

#7

Good spark from the coil tends to suggest that the coil may be good, but you’d have to actually measure the spark to be certain that the coil is good. if you have a spare, or one you can borrow from another car, try swapping them.

If the spark is equally weak on all positions of the distributor cap, the rotor is bad. If weak only one some of the positions the cap is bad. Unless they have been replaced in the last 10 years (more frequently is better) the odds are that the ignition wires are degraded and should be replaced.

#8

yea i have a new coil i had him get just to test and make sure but there the same spark. the wires are factory from 87 which i wanted to smack him for that one i thought he replaced them when he got the car but he didnt. so he has a set coming they should be here this week ill check the rotor but its new he just got it friday but i know even new stuff can be bad.

thanks jim and ranger for all the help ill let you know when i get them on.

#9

Ok so just got the wires on. and cleaned all the grounds still no spark out the wires.Any more help would be greatly appreciated.

#10

I once had an AMC (be kind, it was a gift) with the same failure mechanism. It turned out the rotor itself was open between the center conductor and the edge conductor. I never did arrive at an adequate explanation for how that was possible. The conductor between was covered by molded plastic, it must have failed in there somewhere. Other silly ideas, is the carbon button still in place in the cap? Is the little spring between the carbon button and the coil wire conductor in place? Do the wire set plug ends make good electrical contact with the distributor cap sockets? Ie if you pull the boot back, can you feel the wires sort of snick into place when you plug them in? Do all 6 plug wires have the same weak spark at them or do some have good spark while others don’t? Etc.

#11

ok heres the deal its getting spark out the cap its just weak. nothing out the wires.new rotor cap tried two different sets of new wires still nothing out the wires all the connections are good. on dme pin 1 shouldnt it be getting a ground pulse for the coil while turning it over or no?It just seems like its not getting a strong enough spark to travel thru the wires

#12

The fact that there is any spark at all means that the problem can’t be before the coil. One way or another, the problem is coil or beyond. Don’t get distracted looking at the DME. Start removing ignition parts that “you are sure are good”, and put on other parts. Either a “known good” part isn’t, or a part is installed incorrectly.

Also, keep in the back of your mind that if your “weak spark” idea is wrong, this is all a while goose chase. Is there another way to test spark strength?