TTurner

So I have checked around on the forum and I have read on some of these issues but I'm still coming up empty here are the following thing that has been done to the truck that is not factory...

The truck is a 1988 F150 5.0L Dual Tank:
No cats
Shorty Headers
SMOG Delete
EGR delete

Parts Replaced:
IAC
TPS
MAP
Tune-up
All new fuel pumps in tank and frame rail
New fuel filter
Checked all relays

So I am having the dreaded engine stumble it is there when the truck is cold, warm etc. always there basically. Fuel pressure is 32 psi I know a little lower than normal but still good enough. The truck has small moments of glory where it runs like a scalded dog. Everything I tested seems to be testing fine but I'm running out of ideas to try.

It's not a fuel pressure issue from what i can tell seems to be ignition related somewhere. I cant think of everything I tested off the top of my head but if you throw out a question i will answer asap. Im running out of ideas on this one.

If i fluctuate the throttle everything seems ok..... If it idles it eventually dies and if you hold the throttle at any RPM steady it will stumble like crazy.

Thanks

Chris_1

iTrader: (1)

It could be electrical (ignition) and of course at this point you really should do a compression check.
Brand new plugs can be bad sometimes. Just takes one.
BUT all brand new fuel pumps and only 32 psi is a major red herring. You don't say if that's KOEO or idling but anyway it's way too low for new pumps. Should be looking at 45 psi.
Bad pump or a restricted filter or kinked line maybe. Clear that up first then see if you still have a problem.

TTurner

OK i will take a look at that again. It was 32 idling

TTurner

KOER @ idle 32 psi
KOER @ idle w/ regulator line disconnected 40 psi

KOEO trouble codes: 34 & 15
KOER trouble codes: 21, 41, 34, 13

Thoughts?

MPFit

I’d start with codes.
21 is an ECT sensor issue; mine had it- yet when I tested the sensor it passed. Got tired of it and replaced sensor- code gone and runs much smoother. However it is also a code thrown when the test wasn’t performed on a warmed up engine.

wde3477

Here is a table of codes - http://straighttalkautomotive.com/OBD1/ford-OBD-I.html

Wondering what kind/quality of parts used for tune-up...?

vjsimone

Motorcraft MAP sensor?

Have you checked your ACT - Air Charge Temperature Sensor ?

Code #15 is not good, you may have a leaky Capacitor problem in the EECM.

Re-check your codes for consistency.

TTurner

Used good stuff nothing over the top though im sorry cant remember off the top of my head. The problem was there prior to the tune up and yes i used the diagram for running the spark plug wires.

TTurner

Honestly can't tell you off the top of my head if I have checked the ACT... I will tomorrow though. I'm kinda leaning towards ECM or distributor issues.

There is ZERO rhyme or reason to the sputtering it is constant at all times and all variables.

The MAP sensor was replaced with a non-Motorcraft brand with no change. Doubt that was the problem now.

I will verify codes again tomorrow and try to get the motor up closer to operating temp this time.

wde3477

Perhaps something to verify - pull a plug. Is the spark strong and blue, or more puny, orange, and weak?