707 Gas Engine Problems - Coils?

[convoyduel]

My R608F is coming along nicely. We replaced the floor panels, mat, pedals and broken glass. Running it around the other day, it died like it was out of gas (although I had just put in 26 gallons and hadn't run it much more than 3 or 4 minutes at a time a couple of times since). I got if off the road, put a few gallons in and it started up fine. About 30 seconds later it died. I replaced the stratoflex fuel lines to both large secondary filters by the rear axle and the small paper filter in the bowl on the engine. When I fired it up, it ran like a top but after 3 or 4 minutes, it died again. I checked the filters and all are good and clean. When I loosen the screw on the bottom of the bowl, I get pressurized fuel from the top of the filter cup.

I haven't had a second person around to spin the engine while I check for spark. I was wondering what the collective experience would be with reliability of the coils or symptoms of a bad coil. The caps and rotors are excellent. Wires are good. I find it hard to believe with dual ignition that both coils are bad at once but then again strange things happen. If it is the coil, does anyone know where I can get them? They are big Delco Remy coils with built in cooling fins. Go easy on me, this is my first big gasser.

[hillconst1]

My R608F is coming along nicely. We replaced the floor panels, mat, pedals and broken glass. Running it around the other day, it died like it was out of gas (although I had just put in 26 gallons and hadn't run it much more than 3 or 4 minutes at a time a couple of times since). I got if off the road, put a few gallons in and it started up fine. About 30 seconds later it died. I replaced the stratoflex fuel lines to both large secondary filters by the rear axle and the small paper filter in the bowl on the engine. When I fired it up, it ran like a top but after 3 or 4 minutes, it died again. I checked the filters and all are good and clean. When I loosen the screw on the bottom of the bowl, I get pressurized fuel from the top of the filter cup.

I haven't had a second person around to spin the engine while I check for spark. I was wondering what the collective experience would be with reliability of the coils or symptoms of a bad coil. The caps and rotors are excellent. Wires are good. I find it hard to believe with dual ignition that both coils are bad at once but then again strange things happen. If it is the coil, does anyone know where I can get them? They are big Delco Remy coils with built in cooling fins. Go easy on me, this is my first big gasser.

Coils can be very strange animals. What you are describing sounds like a bad coil. It will start cold but will not run when the coil gets hot. You stop and fiddle with something and the coil cools off and then it will start but only run until it gets hot again. As far as both coils going bad at once that would be very odd, however if this truck has been sitting for a while one coil may have been completely bad to start with and if you had dual ignition engaged you would not know this because the engine would still start. I am not familiar with dual ignition but if you can switch to either side you want, from a cold start see if the truck will start on each coil and they may show one coil as completely dead. Anyway this is just from personal experiance and only a suggestion.

[609albert]

it does sound like the coils to me , try your local napa dealer first , if no success try john chambers in cashtown pa. he has a lot of mack new old stock parts.you could also have a bad coil wire, or bad wire at your ignition switch. post what ever you find the problem.

[Firemack]

Convoy Duel,

Have tested the ignition systems prior to this to see that both are working? It is more likely that you have bad points, rotor, or cap or coild wire than the coils. You should get it running and check to see if it will run on the left then the right then both. I run our B75 on both, but I check to see if it will run on the left and right on a regular basis, and last year found that one distributor seized up and was not working during my check.

Once you can determine if both are working then, check to see you are getting fuel at the carb. sometimes the front fuel pump can be a problem and not providing a constant flow at the carb, or the carb may have a dirty filter, and will run until it clogs up again. Your truck should have 3 filters, 1 at the tank, 1 at the front fuel pump, and 1 at the carb, if these have not all been cleaned and checked, you are most likely looking at a fuel problem as the likelyhood of both igintion systems going at the same time is rare.

If you need the coils they go used for around $100. Napa Coils (not original type) are around $20

Firemack

[convoyduel]

Well the truck has started and run well until this week. The tires are shot so it hasn't been off of the property at the Museum of Transportation. My running around has been on the parking lots and service roads. This week, after running about 3 or 4 minutes, I went to drive it up to the top of the museum, got out on the county road in front and pulling a steep but short grade is when it quit just before the top driveway. That's when I put more gas in it (after about 15 minutes of piddling) and it restarted for around 30 seconds. After we got it back into the lower parking area, we let it sit and that's when I started tackling the fuel system.

This truck has 2 rear fuel pumps it appears - one above the rear axle and one right near the midship driveline brake behind the Waterous pump. Both take a large secondary fuel filter. I replaced the 5 stratoflex style 5/16 inch lines running between the 2 pumps and filter housings, everything else from teh tank up to the front is copper. It looked like the rear most filter was quite a bit older than the midship filter, almost like someone forgot there were two. At the front, I replaced the 2 stratoflex lines that run from the frame over to the block area. I'm not sure what the circular assembly is that one runs to that comes out of the lower mid block on the driver's side. Just past it is a small fuel bowl filter. I've replaced the element in it as well. Everytime this has stalled, there is always pressure in the filter bowl when you loosen the bottom nut to check the bowl.

When the engine was running I always had it on L-R. It ran on both L and R, although there was a few misses when it ran on only one or the other. The last time I ran it on one side was before the thing started dying. Both times it crapped out on me, it was when I got heavy in the pedal.

After I replaced the fuel lines and all 3 filters (took a day or so), it started up and ran like a top for 3 or 4 minutes. When I started getting more confident and running it harder around the lot, that's when it died again. I haven't been back to try and cold start it again. I did remove the right side coil and brought it to my Car Quest guru. I got a big GM style coil and was going to try it to see what I have for luck. Caps and rotors are new and perfect. Wires are older so that's another step.

Will the regular automotive coils work or will they burn out quickly? I'd rather go with the $20 coils new than spend big bucks on something old that is just as bad as what I started with.

[bullhusk]

Look, this is A long shot But is the gas tank venting ? Leave the gas cap off and see what it does ?

[Rob]

Well the truck has started and run well until this week. The tires are shot so it hasn't been off of the property at the Museum of Transportation. My running around has been on the parking lots and service roads. This week, after running about 3 or 4 minutes, I went to drive it up to the top of the museum, got out on the county road in front and pulling a steep but short grade is when it quit just before the top driveway. That's when I put more gas in it (after about 15 minutes of piddling) and it restarted for around 30 seconds. After we got it back into the lower parking area, we let it sit and that's when I started tackling the fuel system. This truck has 2 rear fuel pumps it appears - one above the rear axle and one right near the midship driveline brake behind the Waterous pump. Both take a large secondary fuel filter. I replaced the 5 stratoflex style 5/16 inch lines running between the 2 pumps and filter housings, everything else from teh tank up to the front is copper. It looked like the rear most filter was quite a bit older than the midship filter, almost like someone forgot there were two. At the front, I replaced the 2 stratoflex lines that run from the frame over to the block area. I'm not sure what the circular assembly is that one runs to that comes out of the lower mid block on the driver's side. Just past it is a small fuel bowl filter. I've replaced the element in it as well. Everytime this has stalled, there is always pressure in the filter bowl when you loosen the bottom nut to check the bowl. When the engine was running I always had it on L-R. It ran on both L and R, although there was a few misses when it ran on only one or the other. The last time I ran it on one side was before the thing started dying. Both times it crapped out on me, it was when I got heavy in the pedal. After I replaced the fuel lines and all 3 filters (took a day or so), it started up and ran like a top for 3 or 4 minutes. When I started getting more confident and running it harder around the lot, that's when it died again. I haven't been back to try and cold start it again. I did remove the right side coil and brought it to my Car Quest guru. I got a big GM style coil and was going to try it to see what I have for luck. Caps and rotors are new and perfect. Wires are older so that's another step. Will the regular automotive coils work or will they burn out quickly? I'd rather go with the $20 coils new than spend big bucks on something old that is just as bad as what I started with.

You can test the coils readily with a couple of inexpensive digital multimeters during operation of the vehicle. Keep in mind a coil is nothing more than a step up transformer. The "+" terminal supplies battery voltage, the "-" terminal connects to the ignition breaker points, and the high tension lead connects to the spark distributor to be routed to the proper spark plug in sequence for the engine to run. As you probably know the breaker points when closed short the saturated field of the coil to ground inducing a high voltage into the secondary winding of the coil which is then passed to the distributor. If you lift the lead and connect the negative lead of a multimeter to the "+" terminal, and the positive lead to the disconnected wire, all coil current will pass through the meter. Most coils carry about 200ma, (.2 amps) when running, and most meters will handle this minute current. Carry the meter in the truck cab with you as the truck is operated. If the coil does in fact open up, the current indicated on the meter will go to zero immediately as the engine stalls out. Another way is to use an external pulse generator set at about 200hz, (2000 engine rpm with a six cylinder) with about a 12vpp signal output supplied to the "+" terminal, and the high tension lead connected to a spark plug where the body is grounded. In the scenario the "-" terminal is unused. Either way will put a good duty cycle to the coil. I would change the capacitors also just for kicks. Electrolytic capacitors, (misnomer called condensors) break down with age as I've seen many times. Rob

[convoyduel]

Well, I'm making progress, I suppose. I replaced the ignition coil, cap and rotor. NAPA's coil is an IC64 in case anyone needs the info. It's basically just a simple coil that does not require an external resistor. It also uses a more standard wire, not the screw-down type on the original coils. The kid behind the counter was going to send me packing because the Mack R608F nor anything else with a 707 wasn't in his computer by year, make and model. After I badgered him enough to pull the paper books and look, he found exactly what he needed. Not a big deal, just annoying.

After it ran for a few minutes, it died again. Confirmed fuel to the carb. Pouring fuel down the intake tube into the carb got it to run again but poorly. I finally decided to take the carb off and pull it apart. It's pretty decent inside, but looks like the orifices may have some gunk. The top end with the float looks new and the trottle body does as well. I dropped it off at a local carb shop. After they picked themselves up off the floor from shock (hadn't seen anything this big and obnoxious), they pulled some old books and found a rebuild kit. They say $300 for round numbers and it should be rebuilt. I'll have to see what the results are next week after I get it back.

[1958 F.W.D.]

Here's another one that you probably already thought of, but figured I would throw it out there....The mechanical fuel pump on my 1958 F.W.D. firetruck (Waukesha gas engine) took a crap a few years back- would starve for fuel at higher RPM's while out on the road.

Cleaned filters, blew out lines......Then tested the pump and sure as shit, the rubber diaphragm was torn. Could not find a replacement (Delco Remy pump.) Tried all kinds of specialty antique parts places- Nope.

So I hack sawed off the pump arm, slapped it back onto the block, by-passed the pump through a NAPA electric pump. Runs like a champ ever since.

[Firemack]

Convoy Duel,

The Carb most likely has some sediment in the jets etc, and should have been cleaned and rebuilt anyway to make it run right. I agree with 1958 FWD that the problem could be the fuel system. I had a similar problem with our B75- it would run out of fuel under load. I added a T in line between the fuel pump and carb and added a temporary fuel pressure gauge to watch the fuel pressure , and sure enough the pressure would drop and the fuel pump could not keep up when the truck was under load ,and would eventually run out of fuel, similar to your condition- however you have the electric pump by the tank which could be then getting the pressure back up to carb by the time you chacked it.

I had the fuel pump rebuilt at Kanter Auto in NJ for $80 and $8 shipping. They do a nice job and the fuel pump looks like new- new internal parts, replated and new hardware (also takes about 1 month turnaround)- a little more original than using another electric fuel pump- but it depends on how original you want the truck to be- I did use a temporary electric fuel pump with a fuel pressure block to adjust the pressure to specs. I wanted this truck to look and run like original, so replaced that electric pump setup with the original rebuilt pump.

Firemack