1987 Ford E350 7.5L/460ci/4bbl Super Duty Fleetwood Tioga Motorhome

Troubleshooting / Testing / Diagnostics:

Symptom: rough idle, after heat soak (~1hr) - progressive symptoms, hesitation/miss on acceleration, pop, loss of power, backfire, re-start (5min) after heat soak (1hr driving) resulting in backfire / explosion - 2 mufflers blown apart this week!

History: Rough idle traced to partially disconnected vacuum line. Had driven approx. 1,000 miles with it partially disconnected (moderated hiss). When it completely disconnected engine stalled at idle; limped back home 300 miles and corrected vacuum problem.

Ran fine under multiple short (20 mile tests - city & highway). After heat soak (1 hr highway) exhibits hesitation / pop. Suspected pickup coil. Rotor rusty with rust particles inside distributor. Changed ignition pickup and rotor (Standard Brand LX204/LX206). New Ignition pickup / reluctor gap was ~.024 (spec .007 - .010) and did not pull reluctor to pickup as expected. Gap not adjustable. Fired engine after distributor rebuild resulting in extreme backfire that blew muffler off motorhome.

Mechanics changed distributor to A1-Cardone rebuild (#30-2893). Original distributor (7C05/E3HE/12127/BA). New muffler put on and timing set. Same test run on highway exhibited hesitation after 1 hour on acceleration from 65 to 70. Eased vehicle 55mph back to mechanics, left running 5 min, turned off 1 min, turned back on and extreme backfire resulting in 2nd muffler blown off vehicle!

When problem originally appeared I had changed to my spare new TFI. Mechanic changed TFI (3rd TFI - Advanced Auto BWD - China). Installed and drove same 95 mile round trip test with a 5 min stop half-way. Engine failed to start. Checked coil temperature - extremely hot even after 15 min). Had wife buy replacement coil. 30 minutest later (getting dark) started and drove back home (45miles). Shutdown, waited 5 min, no start. Quickly disconnected coil and temporarily installed new one - started right up.

Next morning: Tested ACCEL's Super Stock Coil #8140 (old and new): primary (old/new): 1.5/1.5ohms; secondary: OPEN/10.58K ohms. Coil (installed 7K miles / 3yrs ago) failed but why?

Checked ballast resistor (49" wire) from coil positive (bat) to TFI red wire (wires and battery disconnected):
Coil Red Wire to TFI Red Wire(1st/2nd/3rd test):
Key Off: 7.4/7.1/* ohms; Key Run: 5.8/5.7.* ohms; Key Start: 4.0/1.8/* ohms
also tested:
Coil Red Wire to TFI White Wire (ballast bypass for starting):
Key Off: 1.5 ohms; Key Run: 1.5 ohms; Key Start: 1.3 ohms
Ford Dura-Spark II spec states .6 - 1.6 ohms between coil red (bat/+) and red wire to TFI. Ballast resistor is used to protect coil after engine is running from voltage overload.

Before I go ahead and attempt to change the ballast resistor wire, a few questions/observations:

(1) Coil Red Wire to TFI White Wire is a straight through (no resistor) wire and exhibits a resistance of ~1.3 ohms at start position. This indicates an internal wire/connector resistance higher than expected (ie: 0.3 ohms), but not huge.

(2) The Red ballast wire from coil and white start bypass to TFI are connected to the ignition switch. Where are the connection points to change this wire at the ignition side. I can identify the coil Red (Bat/+) and TFI wire termination points.

(3) Evaluation/Recommendations: If ignition termination point (Red/White Wires) are accessible AND I can not get 49" resistor wire OR my alternate solution is better:
(a) replace the Coil Red (Bat/+) wire to ignition and install a ceramic ballast resistor (ie: Accel #150250) somewhere accessible in the middle. (b) replace TFI White wire to ignition (coil ballast resistor bypass), straight through wire for starting only.

(4) What if after completing Step 3, the resistance remains higher than normal on the Red and White Wires - indicating the resistance point is somewhere between the harness connector and the ignition switch?

(5) Should I just replace the coil (keeping a spare onboard) and live with the resistance levels.

(6) Is there a better coil to use with a specific primary resistance for this application (high engine compartment temperature - E350 Superduty Motorhome)?

(7) Recommendations: Quality replacement part:
TFI (Blue DuraSpark II)
EGR (oem: D8E-9D475-B2A // Ford Crossed to: D8Z-9D475-B
O2 Sensor (no catalytic converter but has O2 sensor on manifold)

If you have made it this far - I thank you in advance. I have been dead in the water all year. Thank You...

John
1987 Ford E350 7.5L/460ci/4bbl Super Duty Fleetwood Tioga Motorhome

 

It still sounds like a timing issue to me....

 

Just completed test loop (90 miles) after replacing coil: hesitation, loss of power, backfire,and failure to start after heat soak appear resolved.

The Question now is:
(1) Is the out of spec resistance a problem that I need to deal with to avoid premature coil failure OR should I just carry a spare coil and get on the road?

Anyone have recommendations for quality EGR, TFI, O2 Sensor. I have original Motorcraft numbers. Current EGR & TFI (3 yrs old/7K miles) are unknown aftermarket quality. O2 sensor has never changed.

Thank you.

John

 

I drove from Dallas to Reno.
45 mph was my average speed.
if I pushed over that the engine would feel lethargic and back fire.
i just had spark plugs, wires, cap and rotor replaced. I plan to get my timing checked next. I am not a mechanic. Any advice?