Like title says, I have about 4-5 psi at idle and 0 at WOT. I used a gauge that I connected at the VP44. Does this mean new lift pump? Injection pump? 

What's the AC voltage at the alternator at that RPM/electrical load?

Path of speed signal: rear speed sensor at diff, connector at lower left fire wall (C129), ABS controller,  white/orange wire from ABS, connector at upper fire wall (C130)  to PCM. 

I’m not sure. It’s fine in park and neutral at any rpm. But once I get about 35mph  it gets pretty bad.

Edited June 27, 20204 yr by ColoradoColt

Try driving with the ABS controller disconnected.  The only signal to the ECM from the ABS is the brake switch sensor, I don't think that is a problem.

2 minutes ago, IBMobile said:

Try driving with the ABS controller disconnected.  The only signal to the ECM from the ABS is the brake switch sensor, I don't think that is a problem.

I’ll try that! Do you know the location of it? 

Left side of engine compartment.  Those extra wires in the pic are for testing the rear speed sensor output and the signal frequency from the ABS to the PCM.   The small connector is for power and the larger one is for signals, in and out.

 

No change with it unplugged. 

Could cam position sensor cause this?

13 minutes ago, ColoradoColt said:

Could cam position sensor cause this?

I think it would code for a problem.  Why do you think that it might be a problem?

Did the scanner's live date show the same speed and rpm readings?

What is the AC voltage at the alternator with same electrical power load and truck speed?

 

3 minutes ago, IBMobile said:

I think it would code for a problem.  Why do you think that it might be a problem?

Did the scanner's live date show the same speed and rpm readings?

What is the AC voltage at the alternator with same electrical power load and truck speed?

 

I only ask because my Uncle owned the truck before me and I asked him about it and he said he remembers the cam sensor causing RPM problems. The scanners live data only showed rpm not speed with it unplugged. I’m not sure how to measure Ac noise while driving down the road.

Edited June 27, 20204 yr by ColoradoColt

2 minutes ago, ColoradoColt said:

how to measure Ac noise while driving down the road.

With a long jumper wire into the cab.  One end attached to the B+ alternator terminal and the other end to a good quality volt meter.   

 

Okay I’ll check that. I noticed it doesn’t surge if I keep the throttle position under 10%

Edited June 27, 20204 yr by ColoradoColt

Kind of sounds like a transmission locking/unlocking issue, @ColoradoColt you say it starts to surge at 35 -40 mph, Does if feel like transmission torque converter is rapidly locking and unlocking? This could cause a surging effect

5 minutes ago, 01cummins4ever said:

Kind of sounds like a transmission locking/unlocking issue, @ColoradoColt you say it starts to surge at 35 -40 mph, Does if feel like transmission torque converter is rapidly locking and unlocking? This could cause a surging effect

Yes exactly what it feels like. I’ve fixed it before with a bad ground but this time. Way worse and happens all the time. It’s my daily driver so I still have to use it. Luckily I can go 30-35 everywhere in town 

Does it do it at higher speeds like 55 or 60 and faster 

1 minute ago, 01cummins4ever said:

Does it do it at higher speeds like 55 or 60 and faster 

Yes but under 35 it’s fine. Does it less at high speeds it seems like

Edited June 28, 20204 yr by ColoradoColt

It does sound like TC locking issues, and generally it’s ground related, I would start by checking the ac noise at the alternator like @IBMobile was explaining, and doing the w-t ground mod if you haven’t already, it helps a lot and gives you chance to see how the grounds are run and get them cleaned up, and good battery cables and connections are a must, 

 

you might try unplugging your alternator and taking it out a spin. 

Edited June 28, 20204 yr by JAG1

Yes! I planned on doing the ground mod but kept telling myself I didn’t need to. My own fault. Ill get a volt meter tomorrow and see what AC noise I have.

On my way to autozone today it had an awful cut off. Seemed like a governor kicking in or something like my old Chevy... after it slowed down a little starting accelerating normal again. Scanner shows I went 168! Lol

Dash speedometer never went over 45!

Every one of these trucks had too high of A/C volts noise. came from the factory that way. Then as time passes a little deterioration on the grounds and other connections things like your transmission start doing the dance. Drives guys nuts, especially when a new truck payment is 1500 bucks a month for 50 years.( a little sarcasm there) 

 

You need to get on it and do the W-T wiring modifications. It has shown significant results on every truck . I did it to both my second gen trucks and was a huge improvement. Without accomplishing it you are slowly killing your more sensitive electronics and can get not only expensive but difficult to find replacements. I want to say again..... both my trucks shifted fine and yet I still did the W-T recommendations to both trucks. A good volt meter can tell you the same thing you go to the doctor for....... checking high blood pressure. It the same thing on your truck.

 

Also do you have a fuel pressure gauge?

 

These guys will get your truck running so nice.... if you listen to them and don't get lazy...... you will be very happy. Remember short cuts or being lazy is for guys  that love the dealership and don't mind huge payments. 

No fuel pressure gauge yet. I’m currently trying to do the w-t mod.