No spark when cranking until I let off the key?
 

Hey all, I have a 1988 Bronco II 2.9 5 speed 4x4. Ive had it for about 2 years and the other day I put on a new cap and rotor and plug wires. I also cleaned the IAC. After that it ran fine for about a day and then I made a 2 hr trip and cut it off at a store. When i tried to recrank it, it just turned over and over and over for about 10 minutes and then it finally just cranked and ran like nothing was wrong. Its done the same thing twice since then (past 3 days) . Yesterday when it did it, I pulled the coil wire and put a "spark tester" plug in the wire and tried cranking it. It only sparks right at the end when u quit cranking, itll spark 1 maybe 2 times. Itll crank if you just do a few short bursts of turning the ignition key to on. Any ideas on what else to check, or what the problem probaly is? At first i was thinking it was the coil or module, but its only when cranking so maybe an ignition key problem or relay between there? Thanks in advance

oh, and it has done it both after running for awhile and after sitting overnight.

My condolences to you, I am having the exact same problem with my 77 F150. It only tries to start when you let off the key. Never mind the key switch, I replaced it this morning to no avail, ditto on the coil. I am down to the module or the dizzy, but I know it has to be in the starting circit between the key switch and the dizzy. I am not sure but I dont think there is a relay other than the solinoid. Does anyone know if you can jumper from the battery to the hot side of the coil to start one?

I would say you have a bad Ignition Switch.

thanks for the reply.I unfortunatly,before seeing your post, just replaced the ignition switch a few minutes ago and it didnt work for me either. Oh well, atleast it was only 10 bucks and 1 less thing to worry about for awhile.

edit- just saw your post subford, i thought the same thing but a new switch didnt seem to help. I appreciate the reply though, any other ideas?

Your starter solenoid should have two small screws sticking out of it, one is "S" and the other is "I". The one with the "I" has a brown wire going to the Ignition Coil. This wire is off, open or you have a bad solenoid.

If you do not have the two screws then you will have to replace the solenoid with one that does.

It is possible it is the TFI Module but I would look close at the plug and wires that go to the Ignition coil, I have had problems here before on a BII with a 2.9.

I vote ignition module.

I will take a closer look at the wires going to the coil for sure. So theres something on the module that changes when cranking and when running? Cause I have no problems after its cranked, just getting it cranked is harder because the spark isnt there in the cranking position, just the run position. Im not questioning your answers, just want to know how that works. thanks for the help

Replace the ignition module, they get heat sensitive and fail when hot, cool off for a while and good to go again, it's enough to drive you batty.
Take it off and your local parts store should be able to test it for you, if it does test good, replace the coil.

Stock car nut is spot on. There is a 12v wire from the selinoid to the coil (9v) that bypasses th ballast reducer providing full 12 volts while cranking. The starter draws to many amps whille cranking and little spark is produced, thats why it pops when the key goes back to run. See Link

https://www.burtonpower.com/technical/tt_ign.html

Sorry subford it was your post i was refering to.

You guys are not the first to have this problem. The guy I bought my 78 f-150 from rewired and replaced almost the entire ignition system and finnally gave up and sold the truck.

I ddin't think an 88 had the resistor bypass because it has a TFI module? The only thing I am going by on my diagnosis is several people have had this happen on the old Duraspark II systems, and it was the module.

You might take it out and have autozone test it, but since it's intermittent, it may test good at the time they have it on the machine.

Replace the ignition module seen many of them like that in the shop. Also it will not have that wire from i side of starter soliniod unless it has a points type ignition.

chuck