GTSDave

As you may have seen in some of my other posts, I have been fighting a hard starting issue with my truck for a while now. It started doing this a while back and has just gotten worse. This week I had it leave me stranded at a job site. It would not start. Just like it was out of diesel, all the while my pressure was pulsing /pegging the needle when turning over the engine.

I had read that some folks were having issues with the pressure being too high when cranking causing a no start problem. So I pulled the fuse on my Air Dog and the truck started instantly. I put the fuse back in and went on my way. It left me two more times and both times I pulled the fuse, and it started instantly. There are no VP44 codes in my system, so I decided to put in a relay to kill the Air Dog while cranking.

I used a CarQuest P/N 56-1556 relay and wired it in to the harness that came with my air dog. I also bought a spare for the glove box in case this one ever fails. It is rated for 40 amps.

For the install, I took a little different approach than some others have suggested with the FASS fixes I have seen.

This CarQuest relay has a normally open and normally closed set of contacts. The two black wires in the Air Dog harness connect the factory Dodge harness to the the large relay coils in the Air Dog relay.

1) I clipped one of the black wires in the Air Dog harness that runs to the Air Dog relay coils, interrupting the power to the Relay.

2) I then extended the wires to give me some working room and connected them to the normally closed contacts on the CarQuest Relay.

3) Then I connected one of the coil connections on the CarQuest relay to ground. Then connected the other wire to the stater relay under the hood using one of the little fuse/blade extenders.

The way it works is when I turn the key to the start position cranking over the engine, the starter relay energizes which also energizes my CarQuest Relay.

By using the normally closed contacts of the CarQuest relay they open up when I am turning the starter, cutting the power to the Air Dog relay and shutting down the Air Dog.

This gives me 0 pressure on my gauge, but as soon as I release the key to the run position, the CarQuest relay powers down closing the contacts to energize the Air Dog relay and the pump kicks on.

I did it this way because if the CarQuest relay coil fails it will fail to the on position allowing my Air Dog relay to work normally. Also doing it this way keeps me from applying power all the time to the CarQuest relay. It is only powered up when the starter is turning over the engine.

When I just turn the key to run, I still get my little 2 second bump on the pump. I got used to hearing it when I am waiting on the grid heater. Now when I crank the engine over the pump shuts down but if I release the key before the engine starts, the pump still has that 20 or so second run to prime.

It only cuts off when I turn the key all the way to crank the engine over. The rest of the time it works just as it always has.

I will update in a few days as I get some more miles on the truck, and a full tank. It seems I had more problems when my tank was topped off before.

-Dave

KATOOM

I've been preaching this fix for some time now and I had learned it from another member on another forum. Saved me lots of time and money. This person also created a diagram which shows the color coding and placement of the relay to help clarify the process. Hopefully more people will read this thread because I think this problem plagues far more guys out there than anyone currently knows. Especially with the rush of guys installing aftermarket high volume fuel pumps like the FASS, Airdog, Raptor, etc. Problem is that for a long time, the general consensus has been that if you ever had problems getting your engine started or keeping it running then it must be a bad VP. Well this isn't a fix all by any means but its a 10 second check that could possible keep lots of guys from shelling out $1000-$1500, only to find out that their problem didn't go away.

This thread needs to be a sticky.....not that most inquiries over hard starting a warm or hot engine wont continue to be asked.

swordfish

I had the same issue with my Airdog. I was getting 23psi at idle and 21 at WOT. Always had hard starts when the truck was warm. I was told by Airdog to cut down the spring to reduce pressure. I am now at 14.5 at idle and around 12 WOT and no hard starting issues when warm. The high pressures didn't really sit well with me so I wanted to lower them. Not sure why their smallest spring caused such high pressures, but I wanted them lower, this killed two birds with one stone. Of course what I did can only be undone if I get a new spring. My my two cents. If my pressures would have been lower, I would have looked at doing the relay....I am just not that good with electrics.

KATOOM

I'm not saying Pureflow was wrong to give you such advise about reducing your pressure so low but..... we VP44 users are at a stage in time where we're trying to determine whether or not the fuel pressure should be set over 14 psi all the time so that fuel is constantly passing the overflow valve, keeping the VP cooler. Because of this hot start issue, there's guys out there reducing their fuel pressures to bandaid one issue and possibly gaining another with excess VP heat. Unfortunately these kind of trails take a long time to find out if they indeed work or not.

swordfish

You make a very good point. I did not look at it from that angle. I guess I could always get another spring from PureFlow (I hope) and install a relay. In fact, just sitting here now makes me wonder if I chose right. Can I get another spring from them or am I out of luck?

bowhunter57

I read somewhere that you can hook up to the wiper fuse and it will do the same thing, only supply power when NOT CRANKING the engine. Did anybody try this yet.

GTSDave

The wiper fuse may work, but then you would need to use the normally open contacts on your extra relay, and it would be energized all the time and de-energize when you are cranking the engine.

Both will work, but I prefer to have the relay only energized when cranking and off the rest of the time.

Just got back in and so far all morning it has worked great!

-Dave

jncornett

Thanks for posting this up!! 2 guys here at the fire house are having hard starts since its gotten hot..... One has the fass 150 and the other has an airdog 100... Looks like we will be installing a couple of relays for these trucks

GTSDave

jncornett,

They can do a quick check by pulling their lift pump fuse at the next hard start. If it lights right away with the fuse out they have found the problem.

Mine is still lighting right away! To celebrate I ordered a new dip stick and dash pad yesterday from Geno's. Broke the dang handle off my dip stick working under the hood LOL.

-Dave

dkenny

this hard starting happened to me today..but my fuel pressure was 0 so the pump wasn't running any way.

not sure if my case fits exactly..i went to start the truck after sitting for about 2 hrs..it started then died..like 2 seconds later..then wouldn't restart..and 0 fuel pressure..I justed cranked on the starter the fuel pressure went up to around 10psi( normal is 18psi)..then it started..run fine after that?

so something is going on..it only happened a couple of times..this time there was 7/8+ of a tank so its not fuel level..

-dkenny

KATOOM

Maybe you might want to keep an eye on your fuel pressures and see if there's any strange fluctuations. If so then call Pureflow.

GTSDave

Just a quick update folks,

The relay fix worked for me. I have run 2 tanks of diesel through it and the hard starting issue is gone. It is finally fixed.

-Dave

KATOOM

Sweet.

GTSDave

Dangit, Jinxed myself...........

#$%&*$@, truck went to missing about 10 sec after startup today.

Lit off instantly and while waiting for it to warm up, after about 10 sec, it started missing. Running on 2 or 3 cylinders.

Started and stopped it several times and it stayed idling on just a couple of cylinders. When I put it in gear all of them lit, but had a dead peddle.

Managed to back it out of the driveway at idle and move it over one spot to get the Roadrunner out to get to to work.

Read the codes with my smarty.
P0251 Fuel Injection Pump Mechanical Failure Fuel Valve Feedback Circuit
P0252 Injection Pump Fuel Metering Control "A" Range/Performance
P1688 Internal Fuel Injection Pump Controller Failure
P1693 Generic fault indicating a fault in the bus or PCM/ECM interface
P0602 Control Module Programming Error/NotProgrammed

Cleared the codes and put the stock flash back in.
Fired it off and the same thing happened. Checked the codes and it had rewritten all of them again.

Looks like I will be ordering an injector pump today.

-Dave

KATOOM

Is your VP the original or a replacement?