93 Ford econoline van 5.8L misfire

Hello everyone, this is not my "confort zone" car, then i will need all the support you be willing to give me guys. Besides is an old car, i know nothing about this engine/system.

I am trying to do my best studying how to pull codes and how this system works.

The customer complains of hesitation and sometimes when engines is hot, suddenly shuts off.

The first thing i tried, was pull DTC's. It showed (121) TPS out of range - (327) evp below minimum voltage - (565) canister purge failure.

TPS voltage is 0.68v (which i think should be 1v).

First question. It is necessary to tear down intake manifold to adjust TPS.

Second question. Can be hesitation/misfire a symptom of TPS out of range? My instinct tells me not.

Second i tested exhaust gases. 13.2% CO2 - 0.8 CO - 240 HC - no oxygen available.

I couldn't see any O2 sensor, neither cats (i will check again tomorrow).

Third question. Do these engines have O2 sensors?

I cheked spark power at all plug wires and they can jump something like 1 inch (25 mm).

Available tools: scopemeter - exhaust gas analyser - acetylene gas

Ignition control modules were very common failure for hot engine shutdown on that vintage ford. I usually would remove module, hookup to module tester & heat module a little with heat gun to test.

Hi matts,

Thanks for suggestion. Is it inside distributor?

I will do that.

If I remember correctly that year was located on left inner fender well. The later models were mounted externally on distributor housing

guafa wrote: TPS voltage is 0.68v (which i think should be 1v).

First question. It is necessary to tear down intake manifold to adjust TPS.

Not that I know of? But I'd have a new TPS on hand before tearing it down. Those fail all the time.

Second question. Can be hesitation/misfire a symptom of TPS out of range? My instinct tells me not.

I'd agree with a hesitation, especially if there are other dead spots in the potentiometer sweep. Misfire? Not so much.

Second i tested exhaust gases. 13.2% CO2 - 0.8 CO - 240 HC - no oxygen available.

It's been awhile since I took the L1. :blush: Those seem like reasonable numbers?

I couldn't see any O2 sensor, neither cats (i will check again tomorrow).

Running a KOER Self Test will confirm or deny this. If you don't get an O2 stuck lean code, you can be reasonably sure there's an O2 in there somewhere.

FYI, the KOEO and KOER tests are you friends with these vehicles. Run them often during your diagnosis and after your repairs to make sure the PCM is a happy camper.

Third question. Do these engines have O2 sensors?

Usually, yes, one upstream sensor.

(327) evp below minimum voltage

Another common problem, except this won't cause any driveability issues. I'd say ignore this one until you get the stall resolved.

The real fix is usually an EVP sensor, but I've successfully corrected this code by shimming the sensor plunger with a .22LR casing. :lol:

Ok, thank you guys, i'll keep everything in mind.

Due to until now engine is not shutting off, i'm gonna stay focused in hesitation.

I have noticed that hesitation occurs when CO is decreasing less than 0,8%. Then pcm acelerates engine a little bit until CO level increases to 1.4%, when hesitation starts again. This drives me to a fuel issue and remembers me a carburetor.

Am I lost or it makes sense?

Today updates

I cheked TPS voltage. It went smoothly between 0.68v to 4.3v, which i think is good. It is out of range (dtc 121).

KOER showed me (dtc 121 again) and (dtc 327)

Fourth question. Dtc 327 is also related to EGR signal?

I also checked for secondary ignition and non conclusive waveforms were found (see screenshoots for the same cylinder #7)

Finally i checked for O2 sensor activity. Bias voltage (O2 sensor unplugged) was 0.43v. when engine running (O2 sensor plugged) voltage was steady at 0.56v (always, even when WOT). Heater was always ON (0.4v in heater ground wire and 12v on power wire).

Fifth question. Is this pcm designed to control at that voltage (0.56v)?

With this pcm/design i feel like trying to talk with a crying baby. You don't know if is hungry, sick or urinated. Thanks again for your help.

Today news,

I have replaced O2 sensor and usual activity returned like any other system/pcm (voltage oscillation between 0.1 and 0.9). Also it jumped to 1.1v at WOT.

I ask before for TPS adjust but i still need a detail. Is there a way to adjust TPS idle voltage, since TPS has not adjusting holes?

I saw only drills to screw it in only one angular position.