7.4l Now no start

[smokymtn65]

Best thing to do is start by graphing the waveform. So we have an idea where to go with the diagnosis

Would you be kind enough to explain waveform please? I hace a lot of learning to do. Lol i have a cko tech2 and topdon Phoenix lite 2 . Thanks in advance , plugs clean btw.

 

[454cid]

It's just graphing the sensors output over time. It looks like you've already done that with the other sensors. I did that on one of my Volvo's with the TPS. The TPS would short to 5 volts suddenly and that's when the car would suddenly downshift because the ECM thought I had just gone WOT. I then replaced the TPS and all is well. No codes were set becasue the ECM didn't realize it was getting bad data becasue 5 volts is a valid TPS value. It could be that your crank sensor shorts to ground, which likely isn't valid, so you get a code. It could be in the wiring, too.

 

[smokymtn65]

Finally between rain, work and life i got a spark tester. No spark on cyl1 but it did pick up on timing light so looks like weak spark. Didn't get to try on coil wire yet. Since it is part of the fleet lol not my commuter i will finsh diagnostic tomorrow hopefully, think coil or in dizzy.

 

[smokymtn65]

Ok with the wealth of knowledge and experience on here someone knows the answer! Putting spark tester to work. No love on cyl1, so pull coil wire since it doesn't plug up just slid in beside at video the test, have spark. So back to 1 again nothing. So i pulled wire of 3. Put.wire back on 1, start video and crank the truck started and runs. Ok so i put.wire 3 back on and back to crank no start. So what is issue? Cap & rotor?

 

[smokymtn65]

@Schurkey i saw your post on another thread about pulling plug wire 3. After i posted above. So i guess i have narrowed my problem to a dizzy cap. Anyone make a good one ?

 

[HotWheelsBurban]

I've been very happy with the United Motor Products blue vented caps on my Vortec 5.7s. Burb has had one on it for almost 2 years, most of that time we drove it every day in Houston traffic,in rain, cold, Gulf Coast heat and humidity, no issues! Their new cap and rotor on Rawhide really helped the truck run smoother, it idles much better than it did before those parts were changed. Their cap had brass contacts and a vent on the top, and the rotor also has brass contacts.

 

[454cid]

@Schurkey i saw your post on another thread about pulling plug wire 3. After i posted above. So i guess i have narrowed my problem to a dizzy cap. Anyone make a good one ?

I've got AC Delco. I have over 300K on my truck and it's had exactly 3 caps in total. The original, and two AC Delcos. I do have the UMP blue cap that HotWheelsBurban mentioned, but I haven't installed it yet.

 

[smokymtn65]

I've got AC Delco. I have over 300K on my truck and it's had exactly 3 caps in total. The original, and two AC Delcos. I do have the UMP blue cap that HotWheelsBurban mention, but I haven't installed it yet.

Bought ac delco today. But my 07 burb is popping a p0420 so spent time trying to sort that out, but at least i can start it an clear the driveway.

 

[Schurkey]

I do have the UMP blue cap that HotWheelsBurban mentioned, but I haven't installed it yet.

Same here. Bought the UMP cap and rotor based on recommendation(s) on this forum, but haven't needed to install 'em yet.

The failure of the distributor cap at the #3 conductor is not from my personal experience--but I've seen it mentioned on this forum by others. The caps fail at the #3 conductor often enough that I'm confident that it's a design flaw.

 

[HotWheelsBurban]

Same here. Bought the UMP cap and rotor based on recommendation(s) on this forum, but haven't needed to install 'em yet.

The failure of the distributor cap at the #3 conductor is not from my personal experience--but I've seen it mentioned on this forum by others. The caps fail at the #3 conductor often enough that I'm confident that it's a design flaw.

The #3 is the one that has to go over another cylinder 's terminal, correct? That would make sense that would cause a misfire if there wasn't enough insulation between the two.