Check Powers and Grounds

This may seem like a rant but think of it from the customer's perspective. The bill for this truck should have been $450-$500. One hour for diagnosing, half an hour for a fuel pressure test, half an hour for scantool, $200 for part and a half hour to install part. However, I could easily see this becoming a $3000 bill...

Vehicle was a 2007 Ford F150 with the 4.6. Was running VERY rich. The job went to our experienced tech. He has 35+ years experience. He's a great tech. He likes diagnosing and would be considered a great diagnosing tech by most shops. But man... you gotta be better. If you don't like diagnosing and just want to be a mechanical tech then that's fine. Bang out jobs on flat rate and you'll make more money than guys diagnosing. But if you're a very experienced diagnosing tech then you don't get a free pass... Again, this is customer's money we're talking about.

This truck had a MAP code. The MAP sensor is incorporated into the EGR module on this vehicle. So our tech becomes totally fixated on the EGR. Spends lots of time trying to get it off but it's totally rusted. A while later he notices the fuel rail pressure sensor seems to be stuck at 28psi. I told him to hook up a pressure gauge and compare it to the sensor. A while later he actually does. Sure enough the real fuel pressure is 100psi. He then hums and haws for a bit. Pretty simple concept. ECM wants more fuel pressure so keeps duty cycling the pump more and more trying to get that pressure up until it reaches 100% duty cycle. Nothing to hum or haw about. Go after that pressure sensor.

He then tells me he can't find a testing procedure for the pressure sensor. If you're that experienced of a diagnosing tech then you better know how to test a pressure sensor... I told him to check the wiring diagram. It's probably just a potentiometer. Make sure the ground and reference are good. He tells me the computer has some reading so the ground and ref should be good. I tell him to check them anyways. Only takes a couple seconds. He comes back a little while later telling me the sensor is some electric solid state device. It has 4 wires! Who cares?? Just make sure the ground and ref are good. A little while later he comes back all excited to show me that it shares a wire with the EGR. He's still convinced the EGR is a problem... Again, who cares?? That's a 5volt reference. It probably shares that with many things. Stay focused on the fuel pressure sensor and check the ref and ground there.

So he tells Boss-Man to order a sensor. Boss-Man gets nervous because it's a $200 non returnable part. Yet again, I tell the tech to check the ground and ref. Especially for a $200 part. The new sensor didn't help. I asked him if he checked the wires and he said they looked good. He just pokes things unplugged with his PowerProbe. Doesn't take the time to match wires up with the diagram. Just if he gets something that says a power and a ground then he's good. So I grab my meter and start backprobing. The ground is good but the 5volt ref is only reading 0.6v. Well there's your problem... He then genuinely asks me if I thought something was dragging the 5volt reference down... No, I don't think something's dragging it down... I KNOW something is dragging it down. The meter says 0.6v! I checked my connection multiple times. You've been working on cars since before I was born. This is a simple concept! So I start unplugging things on that circuit and as soon as I unplug the power steering pressure sensor the reference returns to 5volts and we get a proper reading on the fuel pressure sensor. That shorted power steering sensor is also the reason for the MAP code.

There are a ton of shops where guys just go by gut feeling and past experience and common problems. No amount of past experiences or gut feelings would ever tell you the reason your vehicle runs like crap is the power steering pressure sensor!!

So the $200 fuel pressure sensor was not needed. Here's the scary part. I can easily see a lot of shops putting a fuel pump in this. These pumps are like $500 plus a couple hours labor. Add on the fuel filter and you're at $800 for the pump and filter. I can also easily see a shop throwing a fuel pump driver module at it. That's $300 parts+labor. Our tech really wanted to change that EGR. After all, it had a code right? That'd be close to $500 parts+labor. I can even see shops throwing an engine computer at this truck... Parts+labor+programming would be close to $1000... Then factor in all the time a lot of shops would have spent on this!

It saddens me that our profession treats power and ground testing to be an advanced subject...

You and I share a very similar plight!

I just had to hand a very good customer a $550 bill that ended up being a loose heat shield and an inner fender rubbing on the wheel...

That's where the value of this community comes in for me.
This forum is (sadly) the only interaction I have with intelligent, knowledgeable technicians.

just out of curiosity where do you tap into to check the fuel pressure on these trucks? I know they used to have a Schrader valve but they went away after 2004 or so I think

cheryl hartkorn wrote: just out of curiosity where do you tap into to check the fuel pressure on these trucks? I know they used to have a Schrader valve but they went away after 2004 or so I think

Right before the fuel rail. Ford has their special fuel disconnects that have a male and female end so you'll need adapters. Separating the quick disconnects on the vehicle is usually pretty simple but sometimes removing your adapter can be stubborn...

Noah wrote: That's where the value of this community comes in for me.
This forum is (sadly) the only interaction I have with intelligent, knowledgeable technicians.

I'm actually lucky in that regard. I have a few resources. Boss-Man and Old-Timer are both very knowledgeable and skilled mechanics. It's just when it comes to diagnosing that it becomes frustrating. Old-Timer is at least quite capable for someone who hardly ever touches a scantool or multimeter. He's knowledgeable about the systems but old school guys aren't able to stop and think for a moment. It's all Go-Go-Go! So they have a very limited ability to draw conclusions from things.

Take for example this mid 2000's chevy truck we had a week ago. Can't remember the engine but it was gas. We did a bunch of front end stuff on it. Key was left in the Acc position which killed the battery overnight. Was stone dead. They put a charger on it but couldn't get it to start. Wouldn't crank. Somehow the body control module fried. But either way I saw them trying to tap on the starter. Old-Timer was manually powering the starter through the relay to make sure the starter still worked. He spent all this time under the hood. Was about an hour before he actually checked for codes. He noticed that there were some loss of communication with BCM codes and he couldn't communicate with the BCM. Took him about 40 mins before he took that seriously and actually started looking at the BCM. When I jumped in the truck I immediately noticed that the PRNDL display in the dash wouldn't select any gear you selected. Nothing was highlighted. Not even Park. That's like having a faulty neutral safety switch. The vehicle will not start unless it's in Park or Neutral. If it never gets that signal then it'll never activate the starter so why are you even checking the starter??

That looks like the OTC kit. That's a real nice set right there! I got lucky and got mine half price. Someone ordered it and backed out, sticking the tool guy with the expense. He sold it to me at cost rather than keep his money tied up in it.

I as for the Chevy no start,
I've seen the mechanics junk cars over neutral safety switch inputs, (and block grounds among other things). They LOVE when I get them running in an hour and drive them back out of the junk yard after they diddled it for a week and told the boss to scrap it.

Good eye! I did grab that image from an OTC kit. We have that one at our shop and it's a good one.

I had an awesome vehicle with a bad block ground! It was an E450 6.0L diesel Powerstroke. The starter is supposed to have a huge ground cable attached directly to it but it was off. The main block to chassis ground was making a poor connection because everything was so covered in nasty diesel oil. The A/C compressor seized and chewed the belt. That was a really unpleasant job on these cube vans... I was so frustrated with it that when I was finished I just bolted that block to chassis ground back where it was. Didn't bother cleaning it. Afterwards it wouldn't start. It was smoking! Uh-oh! The source of the smoke was from the driveshaft parking brake assembly! It was hilarious. The grounds were so bad that it was trying to find any ground it could and ended up melting some rubber in the parking brake cable! When I did a block to battery negative voltage drop I got 8.5V!!! I have never seen a ground voltage drop anywhere near that high before! Heh, so ya, I cleaned the hell out of the main ground and found that starter ground that wasn't connected. After I fixed all that she started like a dream. Or at least as well as any Powerstroke can start!

That's awesome!

would you have the part number for that kit? hopefully it isn't as expensive as the snap on.

The part numbers are OTC 6550 and OTC 6550PRO. I think we just have the standard version. The PRO version will just be some extra adapters. You'll probably be looking somewhere around $350 for the standard and $450 for the PRO. We have the added bonus of having a MotorVac fuel injection service machine. It comes with lots of fittings so when we combine the two we're pretty covered. The MotorVac machine comes with this awesome T adapter with on/off valves.



Most times I need to crack open a fuel line now are just those push clip retainers like on the end of this T adapter. Add some male and female adapters and you're set.



The shutoff valves on this adapter are especially handy if you have a leakdown problem and want to isolate whether it's coming from the rail or towards the fuel tank. Plus it's flexible. Some vehicles have the hard plastic lines going to the rail that don't bend well. So it can be hard to put in a rigid inline adapter like the ones in the top right image of my previous post.

I'm going to be starting a tool review thread soon. Mainly for the stuff I've been abusing from Harbor Freight. If you have one near you, they have a pretty well put together kit for around $80.
I've got the OTC Master Fuel Injection Kit 6550. It's in the fliers for $550, it goes on sale for $450 periodically. Keep in mind, those are the tool truck prices, they're less from Amazon and other vendors.
I got mine for $225.

Even after saving over $300, I still wish I had gotten the Harbor Freight set. (Only because I'm cheap, the OTC kit really is great) They look like even have the same gauge.

It's nuts how expensive these fuel pressure kits are. Heck, even the Gearwrench set is $500... I thought I looked at one a few years back when they were KD Tools that was more reasonable but apparently not... If you were buying this for your own tool collection then I'd have to say go with the Harbor Freight set.

Master Fuel Injection Pressure Test Kit

A shop should buy a better quality set like the OTC or Snapon but for your own personal tools there are better things to spend the money on I would think. Like a high quality multimeter, or an update for the scantool or even a super sexy set of stubby ratcheting wrenches with a flex head!

ecwurban wrote: It's nuts how expensive these fuel pressure kits are. Heck, even the Gearwrench set is $500... I thought I looked at one a few years back when they were KD Tools that was more reasonable but apparently not... If you were buying this for your own tool collection then I'd have to say go with the Harbor Freight set.

Master Fuel Injection Pressure Test Kit

A shop should buy a better quality set like the OTC or Snapon but for your own personal tools there are better things to spend the money on I would think. Like a high quality multimeter, or an update for the scantool or even a super sexy set of stubby ratcheting wrenches with a flex head!

Agreed. I bought this Lisle set and kinda regret it. 90% of the time, I'm using the GM and Ford hoses, almost never touch the adapter set.

Great work on the Ford, BTW