New 5.0L built, low compression and horrible MPG

[1997XLTRollover]

Well did some more work here. One of my fog lights blew out so I tried changing that, swapped the bulb side to side and it didn't work. Ok bad bulb. Put the good bulb back in and now neither damn light works. At what point to I cut bait and scrap this truck? It's been non stop issues and I've only put maybe 2500 miles on this thing. /rant


Now onto business. I checked the EGR vacuum by shutting my hood on my gauge and putting it under my wiper and then going for a drive. Hilarious I know, I was chuckling myself but it worked. EGR pulled maybe 7 psi when at part throttle and nothing when I was on the thottle hard or off the gas. So EGR seems to work perfect. I applied 7 psi using my vacuum pump just to make sure that was enough to open the EGR and it did in fact open all the way. So I'm crossing that off the list of possible issues at least for now.

I then proceeded to test every vacuum line I could find to make sure there were no leaks in the lines. Here's what I tested at idle.

FPR - 20 psi steady

Heater coolant line door control (little canister on top of the heater box or coolant line I forget) - 20 psi steady when heater is off but ZERO when it's on (is this normal?). If I leave the heater off and shut the truck off it holds vacuum and does not bleed down unless I turn on the heat or ac.

EVAP - 20 psi steady

Brake booster - 20 psi unsteady (it averaged 20 psi but shook between 18 and 22) is this normal? Maybe I just had a bad seal because I don't think this is leaking as all lines are new and have hose clamps.

Based on this the only way I would think I could have a vacuum leak now is if the brake booster is leaking internally or the EVAP solenoid is cracked etc. All seals and lines seem to be perfect far as I can tell. Not sure how I can tell if any of the hardware itself is cracked and leaking...??? Might have to just plug vacuum lines at the manifold to rule all of that out at one point.



Now onto the screen shots. I did see some negative values for the ECU trying to lean out the mixture but not much and not a very high percentage. Anyway here's one at idle and one under a load.

Idle:

Under Load:

 

[CorbinDallas]

Subscribing. This is like watching an episode of House, except this time it really is Lupus!

 

[1997XLTRollover]

Ok well I ran the rest of the vacuum tests. Throttle blip came back a little low but I don't think I have any ring issues and it wasn't so low I crapped my pants. Same with steady rpm held, vacuum rises and holds steady.

Then since I have an ultra gauge I set the thing to show me the stft and o2 readings. I then took the truck for a drive. Again it seems to be slightly rich in both aspects which is wrong. But here's where I found it interesting. Took it out and let it rip wide open up to about 70. The entire time my o2 sensors were pinned at .9v and my stft was showing 18%! It's showing pig rich and the computer is responding by dumpingggg fuel. My maf voltages look fine so I'm really leaning toward a bad ecu now. I'm going to clean all fire wall grounds just for good measure but I doubt that's the problem.

So I'm definitely going to buy a computer off eBay and swap it. Question is does anyone know if it has to be from an awd truck? Or as long as I match my SLL4 code I'll be fine?

 

[Dono]

Just match code.
Nothing electrical controls the AWD

 

[1997XLTRollover]

Ok thanks. Anyone have any idea why the brake booster hose only would be unsteady with the vacume gauge? I checked it again with a good seal and it's still shaky. Very odd because all other places I read from the needle is steady. It's just that hose off the booster. I didn't notice any smoke coming out of it when I smoked it so I don't think it has a leak.

 

[1997XLTRollover]

Well swapped the ECU and had no change. Still also have no idea why the brake booster line is shaky on the vacuum gauge either.

Also ordered my new fog light bulbs that decided to burn out at virtually the same time (a week apart) at 35 bucks a pop. Replaced my POS horns that also decided to take a ****. This of course being good that things were getting fixed the truck decided to shred a rear wheel bearing, so now the god damn rear has to come apart. I really wish I scrapped this truck before building an engine.

 

[1997XLTRollover]

Anyone know if there's a way to see how many degrees off the cam vs crank sensors are reading? Then i can avoid taking the timing cover off. If they say within a degree or so in fine, if it's something like 10 degrees I would feel better pulling the cover to check it.

 

[rb142]

Well, you can do it with a scope, but it isn't simple to do. The CAM only puts out one pulse per engine cycle, and you have to know where it needs to line up on the crank signal with respect to the missing tooth. It's not really very practical. The CAM sensor position isn't that critical anyway, and may be off a bit. That doesn't really confirm the position of the cam.

I don't think cam timing is your problem anyway.


Also, when looking at the fuel trims, be sure to look at both the short and long term. Only those two together tell you whether it is commanding overall rich or lean.

 

[1997XLTRollover]

Well, you can do it with a scope, but it isn't simple to do. The CAM only puts out one pulse per engine cycle, and you have to know where it needs to line up on the crank signal with respect to the missing tooth. It's not really very practical. The CAM sensor position isn't that critical anyway, and may be off a bit. That doesn't really confirm the position of the cam.

I don't think cam timing is your problem anyway.


Also, when looking at the fuel trims, be sure to look at both the short and long term. Only those two together tell you whether it is commanding overall rich or lean.

I kind of agree. I know I set the timing set right and the engine really doesn't run that bad, just seems to have a screwed up fuel issue causing it to be down on power and idle a little rough because of the wacked out mixture.

Honestly I think it's fairly zeroed out as far as fuel trims. Maybe a hair on the rich side. But I don't get any horribly high or low numbers (apart form 18% at WOT). The o2 sensor readings are literally all over the place. .1 .2 .35 .45 .67 .76 .88 etc they just bounce all over. Is there any way to record a video in forscan so I can upload it? Or are there any other parameters I can add to my table that might help us figure this out?

 

[1997XLTRollover]

Another thing I just thought of. Where are my o2 sensors grounded? Maybe I have a weak ground somewhere for my o2's or a short in the o2 wiring?

I also have a code for no EVAP purge. Could I have a broken or bad ground causing that issue and the o2's to freak out?

 

[crunchie_frog]

The O2 sensors before the catalytic converter are supposed to vary, that is what drives your fuel trim. Also, you can check your cam position if you know to dead center on a piston, both valves should be closed, you can check each valve stem with a dial indicator.

 

[1997XLTRollover]

The O2 sensors before the catalytic converter are supposed to vary, that is what drives your fuel trim. Also, you can check your cam position if you know to dead center on a piston, both valves should be closed, you can check each valve stem with a dial indicator.

I know they're supposed to vary but are they supposed to vary all the way from .1 to .9 v? I even saw 1V at one point. I thought they were supposed to very just a little bit around .45?

Far as testing the valves I could do a leak down test to show me the same thing no?

 

[crunchie_frog]

I know they're supposed to vary but are they supposed to vary all the way from .1 to .9 v? I even saw 1V at one point. I thought they were supposed to very just a little bit around .45?

Far as testing the valves I could do a leak down test to show me the same thing no?

Yes, they are sop posed to vary between .1 and .9. As far as the leak down test being a similar check, I agree, I thought you said your test results were a little suspect. If it were off one tooth, I am not sure what results you would get on the pressure test but I do believe checking the valve stem movement at tdc would tell you for sure. You might could get the passenger side valve cover off without removing the upper intake and you could check # 6 since it fires at the same timing mark as #1 .

 

[1997XLTRollover]

Yes, they are sop posed to vary between .1 and .9. As far as the leak down test being a similar check, I agree, I thought you said your test results were a little suspect. If it were off one tooth, I am not sure what results you would get on the pressure test but I do believe checking the valve stem movement at tdc would tell you for sure. You might could get the passenger side valve cover off without removing the upper intake and you could check # 6 since it fires at the same timing mark as #1 .

Would I even be able to notice 2-4 degrees difference in the cam timing. I don't think I'm off by a tooth, if anything the timing set had 3 marks on the crank gear, one for 2-4 degrees retard one for 2-4 advance and one for stock timing.

Far as my leak down yeah it was screwed up because the hose I had would not fit in the 302 plug well. I ground down my leakdown tester fitting but I have to go get the hose crimped on again somewhere before I can try again. Unless someone knows where to get a replacement leak down hose that will fit the 302 plug well.

 

[1997XLTRollover]

Also does anyone know what the fuel pressure is supposed to be? I'm looking over my pressures again and to me they just seem like they could be low.

 

[SoHK_alumni]

Fuel pressure is variable, 2.0 to 2.5 bar, approx.28 to 35 psi.

The regulator will drop the fuel.pressure when vacuum is applied. The deeper the vacuum, the further it scales back the pressure.

The later returnless system uses a fixed 4 bar system.

 

[1997XLTRollover]

Fuel pressure is variable, 2.0 to 2.5 bar, approx.28 to 35 psi.

The regulator will drop the fuel.pressure when vacuum is applied. The deeper the vacuum, the further it scales back the pressure.

The later returnless system uses a fixed 4 bar system.

Well what is the actual Ford spec for key on engine off, key on engine at idle and key on engine running part or wot?

 

[4pointslow]

Fuel Pressure

Well what is the actual Ford spec for key on engine off, key on engine at idle and key on engine running part or wot?

39.15 Key on engine off (pump running)
With engine running the pressure will change according to engine vacuum.
The formula for vacuum to psi is..
1 in. HG = .49 psi
so if you have 20 inches of vacuum you should have 9.8 lower fuel pressure
29.35psi

You were driving with the fuel pressure gauge hooked up under the wiper blade, that's what a diagnostic technician would do. Did the fuel pressure drop at wot or did it stay at aprox 39 psi?

Also O2 sensors only sense oxygen, not fuel. High voltage means rich(lack of O2), low voltage means lean(lots of O2 in exhaust). (a mixture is rich or lean on fuel) The normal operating range of a Ford narrowband O2 sensor is 0-.9 (they should vary at least from .3 to .8)
The .88 was a rich reading but you can not say the vehicle runs rich by looking at the split second in time that you captured that O2 reading. That is why we have Fuel trims. STFT and LTFT should be 0 plus or minus 5. So -5 to 5 would be fine. Between 5-10 you have a small issue. 10-15 it is a noticeable issue, 15-20 is a large issue. I have seen codes set on 1996 on up vehicles from 10 and up, but if you don't have a code it doesn't mean you don't have a problem.

If the problem might be A/F mixture related, you need to look at STFT and LTFT at Idle, and 2,000 rpm's in park.
Could you post screens shots of those please?

You want a hose for compression and leak down testing that works, try SnapOn. I have not found a vehicle that mine does not work on yet. (outside of the 3 valve heads with different size threads).

Also to check for restricted catalytic converters you would need an Exhaust back pressure tester, Snap On has those too, they are about $100.00-$150.00. I have video of mine in use at WOT on youtube(https://www.youtube.com/watch?v=O-AY7SKhYX0). I had at least 11 lbs of back pressure, Ford says no more than 8. Idle should be no more than 2-3lbs.

 

[4pointslow]

Purge

Another thing I just thought of. Where are my o2 sensors grounded? Maybe I have a weak ground somewhere for my o2's or a short in the o2 wiring?

I also have a code for no EVAP purge. Could I have a broken or bad ground causing that issue and the o2's to freak out?

In an earlier post you said you disconnected the vacuum line and plugged it, that would cause a code for no purge.

 

[4pointslow]

Wot

Took it out and let it rip wide open up to about 70. The entire time my o2 sensors were pinned at .9v and my stft was showing 18%

At WOT the pcm is supposed to go into open loop and run a richer than stoichiometric A/F mixture. The pcm will also ignore the O2 sensor readings at WOT. The PCM considers 70-100% throttle to WOT.

As far as the scan tool displaying 18 on STFT at WOT it may just be something that the scan tool does, checking the readings on a vehicle with no problems would show you what that scan tool would do in normal conditions. Different scan tools have different characteristics, try looking at STFT on the X3 or X4 at WOT. They usually show commanded A/F.