AnotherBoss

Just bought a 1990, previous owner said it didn't have spark, when we got home, we tested for spark ourselves, and it has what seems to be weak spark. Replaced the cap and rotor to be on the safe side, has fuel going to fuel injector rail, but will not start

Any Ideas?

Shade133

id start with the coil. check it make sure the spark is strong there. if it is, you know its somewhere between it and the spark plugs. if its weak. or non existent then id lead toward the crank shaft positioning sensor. it controls timing and spark and is well known to go bad. also if you replace it make sure the fly wheel is straight because if its not the CPS wont read correctly or at all.

cherokee77

#1 Are the injectors pulsing?
#2 Where are you getting spark from?
#3 Have you tested the CPS sensor?
#4Check the grounds behind the oil dipstick And at the back of the head.

elcameano

Man I just picked a 90 yesterday and had problems with it. Ended up being (So far its still running) the weather pack the plugs into the coil. But I had no spark.

AnotherBoss

I read on a thread, that the crank position sensor should read at 200 ohms + or - 75...Ours read at 237. It has spark, but it's not bright blue...and thats checking spark at the spark plug.

Shade133

well describe the spark. is it bright and strong? or is it weak and dull

cherokee77

Sounds like coil or a bad ground.
And yes that reading is right for the CPS.

Check spark from coil, see what it looks like.

AnotherBoss

How do you check the spark from the coil? Also, when you said, are the injectors pulsing, when should they pulse?

AnotherBoss

it's weak and dull.

Shade133

and this is with new spark plugs and wires? and did you check the grounds? make sure their clean tight and no corrosion? if all that is true, id say change out the coil. i cant think of anything else that would make a spark plug weak other then a coil. unless somewhere between the coil and the spark plug there is massive corrosion.

AnotherBoss

Would a bad coil cause it not to start?

Shade133

yes definitely. not a strong enough spark. not consistent spark. will cause it to not start or of it does it wont run. the coil is what provides the distributor with electricity to distribute to the right spark plug at the right time.

but honestly if you havent replaced the spark plugs or at least make sure they are all good. no corrosion or foul. or replaced the cables. or checked grounds or anything else for corrosion then do that first!

check everything. battery cables most common to be corroded. check the cables from the alternator and to the coil, from the coil. all that stuff.

check all that first

AnotherBoss

whats the best way to test at the coil? tested at the plug...The coil wire has 5.5 ohms, does that sound right to you?

Shade133

hmm. testing it im not sure about ive always had spares because i go to the junk yard and take whatever parts i can get my hands on so i have spares lol.

so ive always swapped another in for trial and error.

as for ohms im not sure ohms would be the correct way to test the coil wire.

ohms as far as i understand is resistance and if i understand how it works correctly you want less resistance as possible so the spark will flow freely and quickly.

someone correct me if im wrong but im sure resistance would mean you got a short or ground issue or corrosion issue.

AnotherBoss

We (Dad and I) are going to replace the coil, see if that does anything, because, we've checked for corrosion, we've checked the cables, and have tightened them.