Truck just goes dead while going down the road

plowboy34 · Post by **plowboy34** » Thu Jun 14, 2007 9:23 pm

See, we told you it wasn't that bad...lol. I wouldn't change the tfi unless the prob still exist. You may have fixed it, and I would lean toward that. I don't believe I ever seen a tfi go in and out, either they work or they don't. Since you say the tach just drops I say you were losing electrical power. Just my opinion, which some say isn't worth much.

87ranger · Post by **87ranger** » Fri Jun 15, 2007 4:06 am

how are you powering your cooling fans, are they pulling off of that ignition switch??

cgrey8 · Post by **cgrey8** » Fri Jun 15, 2007 5:53 am

plowboy34 wrote:See, we told you it wasn't that bad...lol. I wouldn't change the tfi unless the prob still exist. You may have fixed it, and I would lean toward that. I don't believe I ever seen a tfi go in and out, either they work or they don't. Since you say the tach just drops I say you were losing electrical power. Just my opinion, which some say isn't worth much.

Yeah, you were right. It wasn't a big deal. I just assumed that there'd be more to getting to hot-wiring a Ranger than that. But then again, my old 78 Courier's wires went right to the key switch and the switch was on the dash, not in the column. You could literally reach under the dash and pull the wiring harness right off the key switch and with a wire with some male spade connectors, you could have the truck running.

87ranger wrote:how are you powering your cooling fans, are they pulling off of that ignition switch??

My truck had a fuse provision for a rear window defroster. I'd never heard of a rear defroster for a truck, but it had a reserved place in the fuse block for one in the engine bay...the big fuse block using those BIG blade fuses. There was no fuse in the slot (nothing has ever used that circuit before), but the female spade connector that accepts those big fuses were there. So I put a 30amp fuse in that slot, found where the wire terminated in the wiring harness, and used that to power my DC fan controller. As far as I can tell, that fuse block is powered by the battery all the time so the fan load shouldn't be going through the ignition switch if that's what you were thinking.

The fan controller does have a no-load trigger wire that I have wired along with the other accessories so the fans turn off when I turn the key. So that power would come from the key switch. The only additional load on the key switch since the V8 conversion that I can think of is an additional HEGO. According to the Ranger diagrams, the HEGO heater wires have their own dedicated switch as part of the ignition switch. When I put the V8 in, it obviously required another HEGO so I tied the Mustang harness into the same wire the Ranger harness used to power it's 1 HEGO.

cgrey8 · Post by **cgrey8** » Sat Jun 16, 2007 8:43 pm

I drove the truck out to the old house tonight. Not a blip! I'm not sure I got my confidence back in it since tonight was a very cool night, but it's at least encouraging.

cgrey8 · Post by **cgrey8** » Fri Jun 22, 2007 8:25 am

Well, I've been driving the truck to and from work now everyday this week and not a hiccup or blip. I think yall hit the nail on the head with the problem being the ignition switch.

I hope I didn't just jinx myself...

cgrey8 · Post by **cgrey8** » Tue Jun 26, 2007 7:05 pm

Well the truck started it's mess again today.

It hiccuped once or twice coming home, then drove fine the rest of the way. I had to make a quick run to the store after I got home for milk and on the way back to the house, it hiccuped once more. So far, the only thing it's doing is acting like it's occasionally misfiring. However it's all too familiar to what happened a few weeks ago where it was completely dieing on me.

I can't fix what I can't reproduce, so I'm going to drive it into work tomorrow. However ever since the last time it did this, I've had a spare TFI and the tools to swap it out in the passenger floorboard. What I don't have is the thermal grease. I've got some left over from a computer processor heatsink, but it's not nearly as much as what comes with new TFI modules. I'm just crossing my fingers that it's the TFI that's causing all this. If I could just get it to happen in the driveway here at the house, where all my tools are (as opposed to on the side of the road), I could pinpoint where things are going awry.

It was hot today, and datalogging my ACT, which is mounted in my air filter, I logged temps in the 120Â°F range when stopped in traffic. And when it hiccuped this afternoon, it was right after sitting at a traffic light with the pusher fans blasting hot air into the engine bay. It hasn't happened enough for me to say definitely that it's heat related, but it sure seems that way right now.

cgrey8 · Post by **cgrey8** » Fri Jun 29, 2007 2:29 pm

I was able to get a datalog of the truck dieing yesterday afternoon after it sat in the driveway and just idled for a good 15 minutes. The ECT maintained steady but the ACT (i.e. underhood temp) climbed to around 150deg. When I lifted the hood just to take a look around, it sputtered and died shortly after. I don't know if it was related or not. I tried cranking a few different times then eventually it cranked back up and ran fine from that point on. I even tried jiggling wires, tugging connectors, tapping things, nothing would make it reproduce. I also can't say that when it happens, it's right after anything special. I'd assume a bad connection would do it when I hit a bump, go around a turn hard, or something detectable like that. Whatever causes this doesn't seem to be affected by something I can do...at least that's the way it appears so far.

So after I got done messing with the truck, I went back in the house to analyze the datalog. The datalog indicates a lean condition that was the onset of the initial fall in RPM. This means two possibilities:

Normal fuel delivery was interrupted
No spark was present causing unburned oxygen to go out the tailpipe resulting in what appeared to be a lean condition by the HEGOs

So what I know is the EEC did not loose power or the datalog would've stopped. I can see the EEC didn't loose contact with the TFI module since each of my crank attempts are clearly defined in the log via datalogged RPM (EEC calculates RPMs off of PIP signals from the TFI, the same PIP wire that normally drives the coil I believe). That tends to indicate to me the TFI module is working.

The only thing between the TFI module and the coil is my MSD unit and the wiring harness. I'm wondering if my MSD unit is misbehaving or if the PIP inputs to it aren't making a good connectio? My tach gets it's signal from the tach-output on the MSD unit. So if the MSD unit is failing OR isn't getting a good PIP from the TFI module, then that would directly affect my Tach (hence why I see the tach drop in RPMs during the dead-time).

Since the problem so far is still very intermittent and still is conforming to my theory of only happening when it's hot, I'm going to run it a little longer as-is. However I can at any moment (i.e. on the side of the road) bypass the MSD unit and plug directly up to the coil. If the engine cranks and runs fine with the MSD unit out of the equation, that's not saying anything good about my MSD 6A purchase. I'm hoping I can identify a bad connection from the wiring harness to the MSD box...that would certainly be a delightfully easy fix.

Assuming all my wiring is solid, does anybody have any experience with expected behavior of ignition units that go bad?

MalcolmV8 · Post by **MalcolmV8** » Fri Jun 29, 2007 4:02 pm

Sad to say but those MDS units are notorious for going bad. I used to see it all the time on the Mustang forums. Personally I've never had one go bad, knock on wood

cgrey8 · Post by **cgrey8** » Fri Jun 29, 2007 4:53 pm

Does MSD warranty them well or are they simply tits-up when they are gone?

I reset all the spade connectors that go to the MSD unit in hopes it was just a bad connection. I bought one of those cross-connect harnesses that let me plug my wiring harness plug into this harness. Then using spade connectors, I connect the MSD unit. On the other end, is a plug that I connect into the coil. I'm HOPING that those spade connectors are just dirty and need to be cleaned off. After doing that, it didn't studder once on the way home. But that doesn't mean much since it went almost 2 weeks without messing up.

Fortunately my setup isn't far from a stock motor so I shouldn't have a detrimental decrease in performance bypassing the MSD box. But I'd like to think it's giving me some benefits. I'll actually be disappointed if I have to bypass it just to find the engine runs exactly the same without it.

MalcolmV8 · Post by **MalcolmV8** » Fri Jun 29, 2007 9:33 pm

You can call MSD and see what they say about replacing it. I'm sure if you've had it more than a year they'll just tell you to buy a new one but who knows.

Next time your truck fails bypass it immediately and see if it fixes your problem.

I haven't messed to much with bypassing it on my blue truck but on my red truck it made a very noticeable difference. The truck's idle went very poor without it and low rpms where affected.

Hardhead · Post by **Hardhead** » Wed Aug 15, 2007 9:49 pm

CGREY did you ever figure out what the problem was/is?

I am having a similar problem but I am running just a coil.

Mine acts like when a person is learning how to drive a stick and they get it to bucking (not from experience of course) that is what mine does at partial throttle, WOT runs good and just off of idle runs good.

cgrey8 · Post by **cgrey8** » Thu Aug 16, 2007 4:41 am

Mine would happen at idle, partial throttle, and WOT. It was competely independent of throttle position or RPMs.

I THINK I found what it was. Ever since disconnecting and reconnecting the spade connectors that go to the MSD unit, it hasn't acted up since.

This would support all the other data I have about the problem with regard to the EEC still seeing PIPs from the TFI, but the Tach (which is fed via the MSD unit) dieing along with the engine. So if the spade connectors between the TFI and the MSD unit were intermittently loosing connection, then this would cause the engine to die, along with the tach, but the computer would still see spark (it gets PIPs directly from the TFI, not from the MSD).

Also the spade connectors for the MSD unit are on a fender well which I'm sure get wet in hard rains from time to time. Since the spade connectors are not the covered plastic ones that fit inside each other, it's easily conceivable that the connections were getting wet and corroding. A little contact grease should prevent that from happening, and if it does happen again, I'll just replace the connectors with those covered ones...and fill them with electrical contact grease.

Unfortunately, your problem and mine don't sound related. Are you running EFI or carb?

87ranger · Post by **87ranger** » Thu Aug 16, 2007 6:20 am

its a power issue, i think you might be intermitantly loseing power to your fuel pump, stick a guage inside the cab and monitor fuel pressure when it does the stumble and that should help you narrow it down

Hardhead · Post by **Hardhead** » Thu Aug 16, 2007 1:14 pm

Guage?

I assume a fuel pressure guage?