300-6 Power Fluctuation and Galloping rpms

[Kaajot]

Hi-

So, I have not cleaned the engine bay out to show how fantastic Red IX is now, but my heavily-modified F-150 received another $1200+ worth of parts and labor in the garage about 10 days ago.

However, since last Thursday (a week after it got out of the garage), it has had a new check-engine light.

Previously the check-engine light was egr/aic related. At the end we found out the Smog Pump had actually broken and we replaced it with a new one and rebuilt all of the evap lines with new 5/32 rubber lines (plastic was 25+ years old and brittle).

We tore apart the manifolds intake and exhaust, resealed it all with new gaskets, swapped the 17-19 PPH injectors with 14-15 PPH injectors (correct size for 300-6 inline), and also changed a gasket on the cover rod on the left side near the distributor to clean up an oil leak.

Fast-forward to last Thursday and the truck started shifting really hard (E40D). I had to pull over and then limped along at 20-30 mph to a friend's house in town near the mechanic's shop. At the end of that the truck continued to gallop and the battery's voltage fluctuated. Finally it died in place and we had to charge the truck later to get it to restart and move.

The battery had plenty of voltage and the alternator shows its supplying power! The only thing I can think of is my mechanic forgot an electrical component or crimped/broke a wire in the harness during the uninstall/reinstall on the evap side? He also originally couldn't get the truck to start up and played with the distributor cap (thinking the teeth had been misaligned) for quite some time before he realized a plug on that side had not been reconnected for the vehicle wiring harness to the distributor.

Finally, we shot codes for 2 hours on Friday night with a regular ODB-1 mechanic's code reader and a really nice tough-book SNAP-ON code reader. None of the machines could pull codes from the engine light or even begin the "Engine On/Engine Off" tests that start with a rev, then ask for cycling the wheel, pumping the brakes, turning the OD on and back off. The tests would not initiate.

The only fault we did see is "Can not detect Engine Cylinders." This is similar to the problem it had in the Fall where it said "Can not detect Engine Cylinder #4"

So, I've got Engine Light on and can't even start the EOR/EOE tests. and have really hard shifting with lots of transmission fluid in. I threw in two extra quarts tonight just to be sure as it looked a little low but was serviceable.

I'm really lost and so is the mechanic. Help?

 

[Kaajot]

Eureka!

Welp, I used the paperclip method to get the codes and Codes 111 and 126 flashed. 126 was the map sensor....

I had just put in a BWD Map Sensor from Advance 2 years ago, thought it couldn't be it and couldn't the the reason why my truck was running like the transmission, alternator, and fuel injectors/distributor were all running like garbage with 5-7 mpg.

So, put the new NAPA Map Sensor in today. Disconnected the battery, reconnected a bit later. And.... got 20+ miles per gallon for the first time in a long time. And it's shifting like butter, can't even tell.

Going to clean up Red IX and get some pictures up now that the engine is pretty. Paint job's clear coat is flaking off, but it's still a nice 1992 Custom F-150 with F-250 mods on the back end.

 

[smokey]

Great you got it figured out.

 

[Kaajot]

Ya, thanks Smokey!

But, I ran the codes again and code 538 keeps coming up using the paperclip method now.

This is reminiscent of all the times it has not been able to detect cylinder numbers on various code reading machines, including some very expensive ones!

I bled the front gas tank down to null where I was almost stalling and then put 1 gallon in it. I drove it with a reset trip and clocked in 13.3 miles for that 1.0 gallon (plus some spare drops no doubt) before it nearly quit on me again.

I should be getting in the 15+ range in the city with a 20-22 mpg on the highway. So, those are my remaining symptoms.

With code 538 showing up, does anyone have any clue on the last bug in my F-150?

 

[fatherdoug]

I'm not very familiar with this generation, but I believe a code 538 indicates improper procedure for a wide open throttle test.

 

[Kaajot]

I'm not very familiar with this generation, but I believe a code 538 indicates improper procedure for a wide open throttle test.

You're right. I didn't goose the pedal -- cycled everything else. Researched later that evening after I posted.

Going to run the test again and see if it's a clean bill of health, in which case, still wondering why I get 13.3 mpg.

 

[fatherdoug]

I'd be ecstatic with 13.3 mpg.

 

[Kaajot]

I'd be ecstatic with 13.3 mpg.

Are you a 300-6 4.9?

I do have upgrades to the axles (F-250 leaf springs, axle, etc plus 1/2" spacers on all four wheels and 10K lb front coil springs). And a 250lb class IV custom bumber/hitch integrated to the truck's frame.

Ranch hands on the front, and mmmm, some LED fog lights plus 1300 lbs of solar batteries and 300 lbs of sand in the bed.

I just remember driving old Red IX from Little Rock to Atlanta and average 20+ mpg at 70 mph. Haven't hit that in a long time.

 

[Kaajot]

I'd be ecstatic with 13.3 mpg.

I guess I've been living in Egypt and swimming in the Nile. I looked up reported mileage for a 1992 automatic 2wd 4.9L and holy cow, here's the link.

https://fueleconomy.gov/mpg/MPG.do?action=mpgData&vehicleID=9271&browser=true&details=on

I must have been imagining ~20 mpg on long highway trips between Little Rock and Atlanta. So the best I should expect is 17, and I've put a lot more weight and larger tires on this truck, so apparently I'm winning big at 13.3 with those batteries in the bed weighing it down.

 

[SuperCab]

Yeah with as much as you're weighing I'd say you're doing ok.

 

[Kaajot]

Update: Gallops were caused by two things. One was a voltage issue form the PCM I believe, but effectively was causing the MAP to die. We warrantied a MAP twice before it stuck (I see I mentioned that part already).

Second issue was an air filter line was falling out or had never been correctly installed when the filter got an upgrade - literally had no clamp to keep it from falling out of the air filter. It's finally properly installed to the filter (it's the smaller one going to the oil/intake manifold area, made of rubber, not the two big plastic air filter tubes). That made all the difference in the world -- think it has not been connected since Fall 2016, no wonder my mileage was terrible.

Ok, so eat your hearts out, even with the extra weight (250 springs, 250 lb bumper with class IV hitch, etc and oversize 31.5" tires on 15" rims and 1/2" spacers pushing them away from the frame for clearance), the truck gets about 14.6 mpg in the city and on the highway I'm somewhere in the 16-17 mpg range on long hauls with nothing in tow.

Yeah, happy about it. Slowly getting there.