Ground problem? What to check? Sudden change in performance

[65-f100]

OK - Sub was running great until about a month ago. Was low on fuel, stopped at a newer high-volume station and refueled. Next day started sputtering and cut off a couple of times and started becoming hard to start. Also low on power and shifting hard. Check engine light on and flashing and have multiple IP related codes. IP is less than 2 years old with little mileage on it and every bit if the fuel system was replaced when I put the pump on. Lift pump is running and I did change the fuel filter.

I've read several posts of a bad ground causing some of these symptoms as well. Before I change the IP (again!) - I'd like to eliminate any other causes. I know about the grounds to the intake from the batteries and the ground on the back passenger side of the intake. What other grounds should I be checking and are there better places to run the grounds instead of through the aluminum intake? Someone told me that the rear manifold ground should be attached to a bellhousing bolt instead of the manifold. Thoughts or suggestions appreciated

[DmaxMaverick]

Not to say you don't have a ground problem, but it's not likely causing the symptoms you describe. Revisit the fuel system, specifically the fuel quality and supply.

[65-f100]

Dmax - you're not telling me what I want to hear man.

If this helps - here are the codes:

PO 251 - IP Fuel Metering Control A Malfunction
PO 370 - Timing Reference High Resolution Signal A Malfunction

A "pending" code was P0070 which my scanner did not recognize

Is there a way to test the fuel quality other than visual? When I changed the fuel filter it seemed to be pretty clear. Other suggestions?

Thanks

[greatwhite]

Those codes can be set if running the fuel too low and introducing air into the system.

They can also be set by a failing optical sensor.

If the check engine light is on all the time your truck is likely stuck in "limp mode" from the codes.

My advice would be to clear the codes (after downloading the freeze frame data) and see if they return.

I'm willing to bet your low fuel condition was the cause. Air in the fuel makes it impossible for the optical sensor to do its job.

If they do return and your scanner can read the "missed counts" on the ip cam reference, see how many missed counts it records.

More than 8 missed counts will set the code.

Unfortunately, if the codes return you're likely looking at an optical sensor fault.

What year is your truck? Sometimes the optical filter harness fails and causes similar symptoms. The bad news is that i believe all the obdii trucks had the op sens harness deleted because it's "filter" was incorporated into the pcm rendering it useless and as such it was deleted by the oem.

*edit: Oopps, misse the "96" in your sig. Check for the optical sensor filter harness. 96 was the first obdii year and some pieces have been know to be carried over by mistake.

Good luck.

[65-f100]

I did clear the codes and they immediately came back on the next start up. Unfortunately my scanner is not sophisticated enough to read the missed counts.

So is it possible to bleed the air out and correct the condition or is the optical sensor likely damaged?

The good news is that the IP has a warranty, I just really don't want to replace it...again.

[Artworks]

Sounds like air. I run my '95 out of fuel and it farted around till I changed the fuel filter and bleed about a litre of fuel , even run some out the water drain. It seams to be ok now. Mine is OBO 1, so didn't set code the same.

[DmaxMaverick]

It could be air, but it's coincidental to your fill-up. Bad/wrong/contaminated fuel will reduce the power, and cause the IP to have fits (for various reasons), among other possibilities.

The P0700 is a tranny code that commands the PCM to indicate a tranny error (triggers MIL/SES lamp). You'll have to read tranny codes to see the actual code (they will be P07xx). Your poor shifts could cause any number of tranny faults. The good thing is, once you fix the original cause, all the codes should vaporize.

Check the fuel. Capture some (pint to a quart, pre-filter) in a glass jar and let it set for an hour or so. Don't agitate it. Examine it for color, sediment, water, gasoline, etc.

[greatwhite]

Is your pump new or a rebuilt?

[65-f100]

Thanks for the input. DMAX - I'll pull a sample and take a look. You say to pull it pre-filter. I normally pull it from the water drain. Should I be getting it from someplace different?

Greatwhite - this is a NAPA reman pump.

If it is air - what is the best way to bleed the system?

[DmaxMaverick]

The water drain is pre-filter (dirty side), so it's OK. I suggest flowing it a bit to eliminate any contamination that may have settled in the filter bowl and the drain line.

Bleeding air is as simple as you'd do during a filter change. Once the engine is running well, mostly, the rest of the air will purge within a few miles of driving. If you have an air problem in this case, it'll be a dynamic condition, meaning that bleeding will only be temporary, and the air will return.

[greatwhite]

Air will "self bleed" if it's just bubbles in the fuel as long as no more is being introduced downstream of the IP.

Since you problem started after a low fuel level, I would suspect that was the cause (if it is air) and it should have worked it's way out by now.

Air bubbles in the fuel messes up the optical sensor. It's a temporary condition if it's air though. The sensor is "calibrated" to look through fuel at an encoder ring in the pump. It "sees" air bubbles and things go all wonky. Then the P0251 and P0370 codes show up.

It should, however, have cleared once you cleared the DTC with your scanner.

I would have suggested the possibility of contaminated filters, but the recurrence of the DTC's does not seem to support that theory.

A large slug of water in there could cause similar issues, but there would have to be an awful lot of it.

This leads me to ask if the pump is new or a reman and wonder if you're into a "correlation does not equal causation" scenario with the fuel low and fill up.

Rebuilt pumps can sometimes be of questionable "quality". Often, the rebuilder will test the components on the pump and if they spec out good they are reused.

The optical sensor is one of those items they like to reused because they aren't cheap and it ups their profit margin if they reuse the old (but serviceable) part.

Thing is, the older Optical sensors were subject to failure. I've been told both for the "too hard" potting compound and for fuel migration into the sensor.

They have also been known to fail for being too "dirty" over time. What this means is the minute black "coke" in the fuel often accumulates behind the "eye" (really just an led IIRC) and interferes with the signal.

Standayne changed the construction of the sensor over the years and the "new and improved" sensor is part number 33883.

My optical sensor went one day right out of the blue. Driving along fine and then poof: stalling, stumbling and code P0251. I tried just about everything before pulling the sensor out to try another.

Sure enough, trouble disappeared.

The thing is; the sensor is not really a field fix.

You can buy another one (approx 300 bucks), scribe a line on the advance cam in the pump and drop the new one in, but it really needs to be done on a test bench for the pump to get it right.

You can get pretty close with a scanner that reads mm3 fuel rate and setting the sensor for the OEM 7-odd mm3 of fuel at warm idle, but it's still only really close.

If it is determined that your IP optical sensor is the problem, I wouldn't frig with replacing the sensor.

I'd get a hold of NAPA and put that 2 year warranty to good use....

[DmaxMaverick]

Ok, guys. Lets not complicate this out of reality. Keep it simple, until simple doesn't work.

Ran fine. Filled up, no other changes. Didn't run fine. Eliminate the obvious, then make your way into left field. No need to pursue untamed waterfowl, just yet.

[greatwhite]

Ok, guys. Lets not complicate this out of reality. Keep it simple, until simple doesn't work.

Ran fine. Filled up, no other changes. Didn't run fine. Eliminate the obvious, then make your way into left field. No need to pursue untamed waterfowl, just yet.

Not out in left field, giving the applicable information for the OP to chase down.

If it turns out to be fuel, good stuff.

If it doesn't, there's other information for him to consider.

:)