1990 5.0 Swapped Into 68 Mustang Problems!!!

Texasag10 · Dec 6, 2014

Problem solved!!! Turns out the ignition wiring in the old 68 mustang was reduced to 8 volts to save the points. I was only getting 8 volts to the run side of start solenoid, and coil. I added a switch on the dash to put 12 volts directly to the solenoid. I am going to call painless performance and see if they will make note of this for people doing the swap into older model vehicles using point style ignition.

Thanks for all of your replies!!

jrichker · Dec 7, 2014

Good work troubleshooting the problem.

I have a note that the DuraSpark ignition had a resistance wire built into the harness on some models of the car. Other models may have used an external ballast resistor. Its' purpose was to limit the current to the coil and points them keep them from burning up. I haven't helped many of the old to new conversions, so that didn't come to my mind.

Duraspark II ignition diagram:

Diagram courtesy of /www.billwrigley.com

See http://webpages.charter.net/1bad6t/duraspark.html for more help.
Note the ballast resistor shown in the diagram: you’ll need that too
If you use a coil from a 78 or later Mustang, you don't need the ballast resistor. The stock 89 Ford/Mustang ignition coil does not need a ballast resistor

hoopty5.0 · Dec 11, 2014

@Texasag10 - First, good deal getting it fixed and running.
Second, I am really curious to see how well your car is running with a factory EFI system that doesn't use the 02 sensors.
Third, Gig 'em. C/O '09 here.

lord_cobra · Dec 12, 2014

I am also curious about how it runs without the O2 sensors. Without them the car would run on the speed density tables, I believe. The car would also have to be tuned properly for this with a wide band O2 sensor. I could be wrong on all of this since I have only tuned GM, but if it were me there is no way I would push the motor very hard without monitoring the air ratio with O2 sensors.

Texasag10 · Dec 17, 2014

Hey,
Sorry for the late reply, the car ran great with no O2 sensors. However, it did run super rich. The only reason I didn't have the sensors was because the car only had long tube headers. My O2 bungs are in the collector just after the headers. Once I was able to get the car running decent, It made the trip to the muffler shop, and now has o2 sensors.

Also, just curious as to what a good guess at hp numbers would be on this engine. The car will never see a track, or dyno. Just a sunday driver and I've had multiple people ask me and I don't really have a good answer.

-5.0 punched .60 over.
-stock bottom end w/ all new components
-trickflow aluminum twisted wedge 170cc heads
-anderson ford n41 cam
-professional products typhoon upper and lower intake
-pro products 70mm TB
-pro products fuel rails and adjustable regulator
-24# injectors
-255 lph inline fuel pump
-stock MAF
-bama tune for 93 octane
-electric fans
-no A/C compressor

Any fly wheel guesses???

jrichker · Dec 17, 2014

There isn't enough meat to accommodate a .6" overbore, that's almost 5/8" of an inch. You must have meant .060. Even that's risky business in a thinwall casting like the stock late model 5.0 roller cam block. The most I have ever heard that was really reliable was .040 oversize.

Don't like what you just read? See http://www.hotrod.com/how-to/engine/0512phr-engine-building-tech-how-to/

7991LXnSHO · Dec 17, 2014

@jrichker
If I read the first post right, I am surprised. Will a MAF car run without the MAF sensor plugged in? If so, does it just guess (calculate) airflow from TPS and IAC and RPM? I figured the MAF was an indispensable part of the system.

@lord_cobra
I think the basics are the same, even if we also speak GM. I have never heard of the stock, aincent EEC IV computer being able to use a wide band O2 sensor, even with programming. But I have read about using a newer Ford computer, and of course there are aftermarket ones that know what to do with wide band inputs.

jrichker · Dec 17, 2014

7991LXnSHO said:
@jrichker
If I read the first post right, I am surprised. Will a MAF car run without the MAF sensor plugged in? If so, does it just guess (calculate) airflow from TPS and IAC and RPM? I figured the MAF was an indispensable part of the system.

@lord_cobra
I think the basics are the same, even if we also speak GM. I have never heard of the stock, aincent EEC IV computer being able to use a wide band O2 sensor, even with programming. But I have read about using a newer Ford computer, and of course there are aftermarket ones that know what to do with wide band inputs.

Yes a MAF engine will run without a properly working MAF. However, it will set code 66 and run in "Limp Mode" with reduced power, fuel economy and drivability. It uses a failure mode table(s) to calculate the safe limits for engine operation.

Got a lot of spare time and have nothing to do? Then read http://www.veryuseful.com/mustang/tech/engine/EECIVInnerWorkings/ Tmoss has some real insight on the inner workings of the A9L computers.

Texasag10 · Dec 17, 2014

Anyhow.. The motor runs fine now. Fixed the low voltage issue and it runs as advertised with the MAF and O2 sensors. As far as the 60 over block.. Not worried about it. My uncle did the machine work. Says they do it all the time. Just get yourself a decent radiator.
Do any of y'all run a similar set up? Have any hp numbers? Just curious.
Thanks

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