351 starts normal, 30 seconds later hesistation followed by rich stall.
07-15-2015, 12:10 PM
#1
Senior Member
Thread Starter
Join Date: Jul 2011
Location: USA
Posts: 628
Likes: 0
Received 0 Likes
on
0 Posts
351 starts normal, 30 seconds later hesistation followed by rich stall.
Hello fellow f150forum members. My dad has a 92' F-150 with a 351 5.8L.
The engine will do one of two things:
1) Not start at all
2) Run anywhere between 5-30 seconds normally then have severe hesitation for a few seconds before stalling.
Fuel system is at 35 PSI (spec is 30-40PSI KOER), flowing approximately 5oz. in 15 seconds. Most likely not fuel system related or bad gas as switching tanks makes no difference. The other tank was filled up at a different station.
Ignition coil is throwing a purple/blue spark and has very good fire.
No codes present.
Anyone have an idea what is going on?
The engine will do one of two things:
1) Not start at all
2) Run anywhere between 5-30 seconds normally then have severe hesitation for a few seconds before stalling.
Fuel system is at 35 PSI (spec is 30-40PSI KOER), flowing approximately 5oz. in 15 seconds. Most likely not fuel system related or bad gas as switching tanks makes no difference. The other tank was filled up at a different station.
Ignition coil is throwing a purple/blue spark and has very good fire.
No codes present.
Anyone have an idea what is going on?
Last edited by bluecar5556; 07-17-2015 at 02:41 PM.
07-15-2015, 10:10 PM
#3
35 psi is low. If that's at idle it's low if it's at key on engine off it's very low.
TPS - .7 is too low, it needs to be adjusted to .9Vdc at closed throttle and should climb to 4.5 to 5 Vdc at wide open throttle.
A couple things to look at anyway.
TPS - .7 is too low, it needs to be adjusted to .9Vdc at closed throttle and should climb to 4.5 to 5 Vdc at wide open throttle.
A couple things to look at anyway.
07-17-2015, 01:01 PM
#4
Senior Member
Thread Starter
Join Date: Jul 2011
Location: USA
Posts: 628
Likes: 0
Received 0 Likes
on
0 Posts
New symptom...
Once engine dies, the coil continues to fire. Is this normal?
The TPS was replaced with motorcraft and adjusted to .9V CT and 4.5V WOT. Cleaned EEC connector at bulkhead.
Here is a video of it running then stalling.
Once engine dies, the coil continues to fire. Is this normal?
The TPS was replaced with motorcraft and adjusted to .9V CT and 4.5V WOT. Cleaned EEC connector at bulkhead.
Here is a video of it running then stalling.
Last edited by bluecar5556; 07-17-2015 at 02:47 PM.
07-17-2015, 10:33 PM
#5
Senior Member
Thread Starter
Join Date: Jul 2011
Location: USA
Posts: 628
Likes: 0
Received 0 Likes
on
0 Posts
Problem solved
These were my symptoms. Ignition coil fired and the IAC actuated even after engine was shut off!
Found a new EEC/PCM/ECM at a salvage yard off of a 92' F-150 that looked to be in good shape. The problem is solved.
Reason why the computer failed is simply this. The gasket in front of the computer was in poor shape and the case was rusty allowing moisture inside. Make sure your gasket is in good shape, this is critical because the PCM is not a sealed unit! After further investigation, all the electrolytic capacitors two 47uF and one 10uF have corroded into dust just about. Also worth noting, the electrolyte had leaked out of the capacitors and when this occurs, the PCB is eaten away by the acid it contains. I've attempted replacing them by wearing away the factory applied rubber coating off the solder side of PCB with a plastic spudger, not to cause more damage, but the pads where the capacitors go were too far gone, even after bridging a trace with a capacitor lead.
I'm surprised it ran as long as it did in that condition!
Found a new EEC/PCM/ECM at a salvage yard off of a 92' F-150 that looked to be in good shape. The problem is solved.
Reason why the computer failed is simply this. The gasket in front of the computer was in poor shape and the case was rusty allowing moisture inside. Make sure your gasket is in good shape, this is critical because the PCM is not a sealed unit! After further investigation, all the electrolytic capacitors two 47uF and one 10uF have corroded into dust just about. Also worth noting, the electrolyte had leaked out of the capacitors and when this occurs, the PCB is eaten away by the acid it contains. I've attempted replacing them by wearing away the factory applied rubber coating off the solder side of PCB with a plastic spudger, not to cause more damage, but the pads where the capacitors go were too far gone, even after bridging a trace with a capacitor lead.
I'm surprised it ran as long as it did in that condition!
Last edited by bluecar5556; 07-17-2015 at 10:39 PM.