Erratic/Intermittent Voltage Drop while Cranking when warm 88' 4.0

[Mikethe80sFanatic]

Hi Everyone,

 

This is my 1st post. I picked up this Comanche a little over a month ago(My first!). It is a 88 2wd/lwb Pioneer 4.0/Aw4. 222k on the clock. The original owner purchased it in Missouri. Lived there for a few years before moving to Florida. Then recently made its way to Michigan to his granddaughter here. When once she realized the amount of work needed. She sold it to the shop she took it too. And I purchased it from them. It still has most of it's original window sticker. it is 100% rust free. It has been repainted at some point.

 

The AW4 was rebuilt about 18k miles ago. The shop I bought it from redid the top end due to a bad HG. all new Cooling system. Still the closed-loop. full tune-up.

 

What I've done: replaced the self-destructing balancer, Timing set, TPS, Starter, Starter relay, Cables, re-freshed grounds. added a ground to the core support from the battery, and I left the body to engine ground strap. but added with it a cable from the body to a intake heat shield bolt.

 

Now here is the issue, which has been present since before I purchased it...It starts just fine when it has sat for several hours(overnight, or while I'm at work. Once it is warm. It struggles to start. It will start cranking strong, then it will slow down like the battery is almost dead, and then pick back up, slow down etc. Sometimes it will start while doing this. Or it may take me a couple tries until it lights off. Then sometimes it will fire up with no issues. But that is very rare.

 

I checked the timing, seems to be where it should be. Battery was load tested and passed. The Alt. charges as it should...14.4v. I jumpered the ballast resistor, no difference. Fuel pressure is at 30-31psi w/ vac. 37-38 w/out vac. the vac line to reg. does smell of fuel, but is not damp. I also disconnected the A/C Clutch and no change. 

 

When it happens. There is a large voltage drop when it slows. I've noted with my volt meter on the batt. It will drop to 9v, even 8v when it slows, then voltage will come back up to over 10v when it speeds back up. I've even tried hooking a jump box to it, and still happens. 

 

I feel that it is some sort of "Heat Soak" Issue. A buddy mentioned possibly the coil. It does appear to be original. I've lurked on this site and have checked countless others. And haven't seen anyone else having a similar problem. I'll post/link my youtube video so you all can see for yourself what I'm dealing with. 

 

https://youtu.be/fAZT_wsADR0

 

 

<iframe width="560" height="315" src="https://www.youtube.com/embed/fAZT_wsADR0"frameborder="0" allowfullscreen></iframe>

 

 

[Mikethe80sFanatic]

[Marine1Texas]

how new is the starter? I had something like this happen before on my 72 chevy not my mj's. It was caused by some one jumping it with a 24volt when the battery died. The starter worked fine when cold, but when need to start again with in a hour it would cycle very slow and pull heavy amps.

Also something to check is if your starter is staying engaged even after you let off the solenoid when starting. The fly wheel could be turning your starter causing it to over heat. I have never had heat soak on my starter and this one is 15 years old now.

[Mikethe80sFanatic]

It did it with the original starter. I replaced when I got it home. Still did it. I had it loaded tested several times in a row. It passed every time. But the wiring from the solenoid to the motor would get hot. So they warrantied it. And no change with this one.(2nd new one.) 

 

It does not sound like it is staying engaged. The ring gear looks to be in good shape.

[Marine1Texas]

Now your got the starter eliminated. Next Step is to check out that Starter relay.

[DirtyComanche]

How was the battery actually load tested?  90% of the tester out there are complete garbage.

 

Being who I am, I'd put the battery from my plow truck in it and try it...  Because as I see it, you've either got a bad battery, a silly issue (loose connection somewhere, you could try making sure everything is tight when hot), or real problems.  2 minutes to check the big ground on the block and big positive connection on the solenoid, and wiggle the battery terminals to make sure they aren't loose when warm, then I'd move on to swapping the battery.

 

If it's real problems, it's a whole post as to of where I would go with that.

[DirtyComanche]

Hang on, listening to it...  Pull the lead wire from the coil to the disty, see if it does it while cranking like that.  If it cranks cleanly until the battery starts to fade (30 seconds of cranking at least), I'm guessing it's actually an issue with too much timing advance during the start.  Why this would be is something to think about.

[buckwheat]

My truck does this same thing occasionally. If I take the main ground wire off the block and clean it really well it seems to help for a few months. Then the issue comes back. Very intermittent. So the only real idea I have for you is to clean that ground off again.

 

I'm going to keep checking back here for any solution you might come up with. Good luck.

[Mikethe80sFanatic]

Thanks everyone for your replies.

 

-I have replaced the Starter Relay. There was no change.

 

-Battery was loaded tested at the local O'reillys. With one of their Handheld deals...Like I said, I hooked my jumpbox/charger up to it. And It still did it.

 

-I have checked, double checked and triple checked my connections cold and warm. But I will check again.

 

-It does seem similar to advanced timing. As My Bronco will crank slow if I have it a bit to advanced. But It's a slow crank right from the start. Where as the Comanche starts off strong and then goes back and forth. I know the timing is non-adjustable. But it should be at 12 degrees when idling correct?

 

-I will try pulling the coil wire and cranking when I get home from work. I will post my findings then.

[Mikethe80sFanatic]

So, here are my findings from yesterday. When the cranking issue came up again. I pulled the coil wire off, and cranked it. And for a good 10-15 seconds, It cranked over just fine. Plugged the coil wire back. and it fired up with no issues several times in a row. I took it for a quick drive. and it started up a few times without issues. I let it sit while I finished up replacing the front pinion seal on my fiance's XJ. And when I came back to start it. The cranking issue came back. I pulled the coil wire, and the FP relay as well. And cranked it over for a good 30 seconds. And it spun over without issue the entire time. Plugged it all back in. And it started up without issue the dozen times in a row I tried. So It looks like I will look into further testing of the coil.

 

While going over this yesterday. I also noted a bad fan clutch. And my O2 Heater relay was much warmer than the other 3 relays. So I swapped it out with the "Power Latch" relay for the time being. I will test the relay this weekend.

[Mikethe80sFanatic]

I came home from work today. I let the truck sit for an hour or 2. I came back out to try and start it. Same issue. Pulled the coil wore off and it cranked over fine. Plugged the coil wire back in. And the issue came back.

 

Any thoughts on where I should start? Coil, ignition module or perhaps the distributor?

[DirtyComanche]

I actually think it's more likely to be an issue with the crank position sensor and what the ECU interprets from it. But if your MAP, intake air temp, coolant temp sensors are providing faulty or erratic outputs it could play into it.

 

I think the coil and ICM are both 'works or doesn't' type of equipment.

[Marine1Texas]

The starter has nothing to do with the ECU, MAP, intake air temp, coolant temp or any sensors it is 100% controlled by the relay which is wired to the ignition, it should crank the same no matter what, as long as he has the volts, amps and the engine is not firing early or late . From what I get from what he is saying The problem he is having is something is taking the amps away from when it starts while hot Or possibly the timing in the distributor is jumping ahead or way behind.

 

For me the check list would be coil pack and the Dizzy.  

[DirtyComanche]

The starter has nothing to do with the ECU, MAP, intake air temp, coolant temp or any sensors it is 100% controlled by the relay which is wired to the ignition, it should crank the same no matter what, as long as he has the volts, amps and the engine is not firing early or late . From what I get from what he is saying The problem he is having is something is taking the amps away from when it starts while hot Or possibly the timing in the distributor is jumping ahead or way behind.

 

For me the check list would be coil pack and the Dizzy.  

 

Didn't read the thread, did ya?

 

Nothing is 'taking the amps away'.  The starter is loading massively, which is actually causing the amperage to go sky high.  The fact that it cranks nicely with the ignition unhooked confirms that it is likely a timing related issue, which is a control related issue, which is ECU and everything that goes with it.  Sure, it could be the disty, but I wouldn't be replacing a thing before I confirmed all sensor functions appear normal.

[Marine1Texas]

I Did read the thread. 

He say this is not happening tell have it has been running, and on the restart, so sensors in most cases don't over heat. He is saying the volts are dropping. That means some where is taking amps or getting ground out. the starter would be cranking if it had the amps, unless the dizzy timing was so far advanced or major retarded to give push back. See for the dizzy to get the ok to fire it needs cps to trigger it from the ECU. He is getting volt drops before the cps can even get a signal to the ECU then send timing adjust to dizzy. So before any sensor, before even the ECU, their is a problem the way I see it.

before you start a Renix up, the ECU has no clue what the timing is at, that is why you have the cps to let the ecu know that the timing is set at ecu specs and when to fire the injectors. If he is getting either push back from advance that sounds like something wrong in the dizzy.

I am not saying to replace the dizzy or coil, I am just saying those are the spots I would test first.

[Mikethe80sFanatic]

Please watch the video I posted if you haven't yet. It will show you exactly what I'm dealing with. 

 

Once its running. It runs great. Revs easy and quick, Pulls hard...harder than my woman's HO XJ. Cruises great. haven't been able to get an accurate mpg yet. No hesitation or stumble.  Only has a slight wandering idle. I've replaced the TPS and adjusted it. And cleaned the TB and IAC. 

 

I know the exhaust has been pieced together over the years. I am unsure of the Cat's condition/age. I know its heat shield is strapped together. I will have to do the vacuum test to check for restrictions.

 

Now, If the coil was bad/going bad. Wouldn't I get more of a "no spark" condition? To me, It seems like the issue would be with the ignition module telling the coil when to fire. Or the dizzy. Does/should the Camshaft position sensor/Sync Signal Generator have any sort of movement to it? For advancing/retarding the timing? like weights and springs in a an older dizzy? The majority of my more serious ignition system dealings have been with Ford Duraspark II systems.  

[Marine1Texas]

watching your video, sounds like advanced timing to much almost. however I would think it would be all the time. to me does not sound like battery is not bad. Sounds like pre detonation before the cylinder is all the way compressed, causing push back and amps to build on starter.

CPS can not be adjusted unless using the advanced timing mod. Other then that no adjustments can be made to cps. With the ECU controlled timing you can not adjust the dizzy timing at all, their is a indexing write up by cruiser on it. I been using HEI setup for 15 years plus and on both my MJ's, but if I recall their is no weights in the dizzy, all ecu controlled. So slacked or stretched timing chain would be the only other way, however I would figure that would be a constant all the time thing. I wonder could a chipped gear on the bottom of the dizzy cause it to advance for a short time? Not sure on that one

 

If a coil go's bad, normally, you get low spark or no spark, and some time intermittent spark. Sounds to me like something is causing it to pre detonation before the cylinder is all the way compressed. Don't sound like starter or coil problem at all.

[cruiser54]

More than likely the injectors are leaking down when it is first shut off. You start it and it's a bit flooded. When it's had time to cool, the excess gas from the engine has also had time to evaporate. 

[Marine1Texas]

cruiser54, on 08 Apr 2016 - 2:35 PM, said:

More than likely the injectors are leaking down when it is first shut off. You start it and it's a bit flooded. When it's had time to cool, the excess gas from the engine has also had time to evaporate. 

Something I never thought about. I never had leaky injectors so I would never of thought about this one.

[cruiser54]

 

cruiser54, on 08 Apr 2016 - 2:35 PM, said:

More than likely the injectors are leaking down when it is first shut off. You start it and it's a bit flooded. When it's had time to cool, the excess gas from the engine has also had time to evaporate. 

Something I never thought about. I never had leaky injectors so I would never of thought about this one.

 

Well, it was an issue back when they were brand new and I was Service Manager at the dealership. The cool thing is I remembered it!!!!!

[Mikethe80sFanatic]

Well, when I bought it. I glanced under the cap and rotor. But it was getting dark and I forgot my flashlight. Fast forward to last night. I figure I should double check. Well the the terminals on the cap and rotor were toast. Which made me check the plugs. They were junk. 2 different kinds and none were gapped properly.

 

So cap, rotor, and plugs later. I haven't had the issue come up yet. It doesn't smell as rich out the tailpipe. Pulls further up the Rev band then it has before. And hasn't given me any issues starting back up.

[cruiser54]

Well, when I bought it. I glanced under the cap and rotor. But it was getting dark and I forgot my flashlight. Fast forward to last night. I figure I should double check. Well the the terminals on the cap and rotor were toast. Which made me check the plugs. They were junk. 2 different kinds and none were gapped properly.

 

So cap, rotor, and plugs later. I haven't had the issue come up yet. It doesn't smell as rich out the tailpipe. Pulls further up the Rev band then it has before. And hasn't given me any issues starting back up.

Spark plug wires? 

[Mikethe80sFanatic]

The Wires will be replaced as well. But bills had to be paid first...Darn Adult responsibilities lol.

[cruiser54]

The Wires will be replaced as well. But bills had to be paid first...Darn Adult responsibilities lol.

Look into Taylor wires. Part # 84248. 

[Mikethe80sFanatic]

Ok,

 

So an update on my Comanche. Replaced the wires...BWD brand for the time being. And so far it has not been an issue. Additionally, I cleaned and dielectric grease the coil contacts.

 

But, I've had a new issue pop up. Which has left me baffled. 3 separate times I've fueled it up. completely...it will start back up right away. 1 time at the pump, and 2 times, I left it running to fuel. drove it home and parked it. Came back out to it 5-20 minutes later. Same thing. Cranks over nice and strong. Eventually it will start...after 20 minutes of messing with it and cranking.

 

What I've noticed when this "Issue" takes place.

 

-When I fuel it up all the way. the gas pump seems like it shuts off late. I.E a splash of fuel shoots out the filler all over.

 

-When I turn the key on...occasionally, I do not hear the pump prime. or it's only for a second, if that.

 

-I "checked" for pressure at the rail. was there everytime. Did not have a Fuel pressure gauge to confirm exact psi at these instances.

 

-The first time it happened. I swapped relays around and it fired up...Which with all these. would make you think a fuel system problem. But I think it was a lucky timing thing.

 

-The 3rd time this happened. I had a spark tester on me. No spark while cranking...at first. after a few minutes. When I would let off the key when cranking, I'd get some weak spark before it stopped rolling over. Then I would start to get random sparks(still weak) while cranking. Then after a few more minutes. it would fire up and run. And would start up every single time after.

 

-If I don't fuel it to when the nozzle stops. this issue doesn't surface. I still leave the truck running still, just in case. I am going to test the CPS. And once I get a little more time. I will drop the tank and inspect the tank vents. But other than that. I'm at a loss haha.