News: 5 Min. Tune Up

[John Robinson]

Every since I bought my car with 67K miles it has upshifted at wot at 4900 RPM. Four days ago I got it hung up on snow and rocked it back and forth with the asr off. During this I got an SES which I ignored. When I got out of the snow and back on clear pavement I noticed that something was differnet in how it was running. I was running about 20 MPH and punched the throttle about halfway and holy cow it took off. Next I repeated the 20 MPH speed and really got on it and it snapped up to 6300 RPM before upshifting. I rushed home and pulled the code and it was a DTC 72. Apparently in going back and forth between drive and reverse I broke something loose between the ecm reading the shift points and the switch on the transmission.

Now when I get on it at high speed it missfires and I get a DTC 55 which I have had before along with 63 and 64. I have taken electrical tape and put a couple of wraps around the vacuum nipples to tighten them up. I can tell you that the car idles much smoother now and am looking forward to another drive to see if this has any effect on the fuel starvation at high speed. Updates as I learn more.

 

[screamin_conure]

Well, it sounds like you cleared out the old girl's sinuses!

Unless I'm mistaken, I believe '93 was the first year the ECM managed shift points on the 700R4. And it sure sounds like you may have ended up with some moisture in the sensor when your car became snowbound (Code 72).

Yeah, I'd be curious to know why you're getting the lean mixture and 02 sensor codes all of a sudden. I'm wondering if the fuel system can't quite keep up with 6k+ RPM operation! hnoes

 

[aklim]

Sounds to me like your kickdown cable was not adjusted right and your snow maneuvers might have changed it.

 

[screamin_conure]

Sounds to me like your kickdown cable was not adjusted right and your snow maneuvers might have changed it.

Excellent point.

 

[aklim]

Maybe he should shut down the engine, reset it back to the furthest point and hit the throttle all the way.

GM TV Cable Adjustment Instructions

 

[John Robinson]

The asr tv cable adjustment has been done multiple times as per the fsm since I have owned the car. In reading the fsm on code 72 it will set if the vehicle speed is greater than 30 mph. I think that the ecm thought the speed was higher than that and it also was confused as to which gear it was in. For some reason this caused something to reset and in so doing it solved this problem. Before we all jump off the deep end and say well then the ecm is going bad the low shift point was also normal with the orignal ecm which was replaced a few years ago. In all probability my throwing the gear lever back and forth probable moved a switch contact point or something like that. I really dont care what it did I am just praying that it will not go back to it's old ways

 

[aboatguy]

1993 has 4l60.....1994 was first year for 4l60E in Corvettes...so it is probably mechanical vice computer issue.

 

[John Robinson]

I have been doing little checks on the car to see if I could improve the fuel lean codes. Here is what I have done so far.

1. Checked all vacuum lines and replaced the line from the ASR because it was brittle and broke off in my fingers. Also replaced the line to the vacuum canister.. Checked vacuum to EGR and EGR vacuum solinoid. They all were in working order.

2. Pulled fuel pump and checked the fuel pump strainer. It was OK

3. Pulled fuel filter and was abel to blow air through it and the fuel that came out was clean. Reinstalled the filter since it was apparently changed by previous owner as evidenced by the marred fuel line nuts.

4. Had fuel pump preassure checked it was 44 #

Will update how the car runs in a few days when the weather gives me a break.

 

[John Robinson]

Fuel Filter

Put a new fuel filter on today and drove the car. It seems to run better now but won't be able to tell for a while because I have to replace the U joints on the left rear half shaft. Even so I did run it up on 3/4 throttle to about 80 and it did not bog down like before and keeping my fingers crossed that all the codes I got were because it was not getting enough fuel flow. Low flow volume would make the system that looks for lean condition go bongers thinking the 02sensor is bad or etc. Spring is coming and by then I should have the car debugged for another year.

 

[LT4man]

The FSM says one should replace the fuel filter when the filter is clogged.

To wait until your Vette stops running to replace a fuel filter is just asking for a breakdown. :W

You were correct, John, in replacing the filter.

I have replaced the fuel filter on my LT4 every 30,000 miles and have never had an issue with fuel flow and/or delivery.

 

[John Robinson]

Fuel Filter

Here are some pictures of the inside of the filter I took off.

I believe that the dark spots are a build up of junk that was trapped by the filter. I also beleive they were causing a restriction in how much fuel could flow through to the injectors.

<a href="Fuel Filter 001 on Flickr - Photo Sharing!" title="Fuel Filter 001 by bj.robinson@sbcglobal.net, on Flickr"><img src="http://farm5.static.flickr.com/4004/4403862982_bd8f643f70.jpg" width="500" height="375" alt="Fuel Filter 001" /></a>

Let me know what you think

 

[gmjunkie]

It was time John,You got your $'s worth out of that one!!:L

 

[aklim]

It was time John,You got your $'s worth out of that one!!:L

I call BS on that. Why, you spendthrifts don't know the value of a dollar. I'll bet you can get at least 1 more year out of it. In fact, if it is cut apart, wash it and duct tape it back and it probably will be good for another few years.

 

[John Robinson]

Fuel Filter

I call BS on that. Why, you spendthrifts don't know the value of a dollar. I'll bet you can get at least 1 more year out of it. In fact, if it is cut apart, wash it and duct tape it back and it probably will be good for another few years.

Thats what I did with the fuel pump strainer I took it out cut it open and washed it out then I sewed it back up and put it back in the car for real no BS

 

[John Robinson]

Fuel Pressure

Managed to get my hands on a fuel preassure gauge today.

Switch on no start preassure is 35.

Switch off preassure holding at 35 and slowly bleeding off about 3# in five min.

Engine running preassure 38

Disconnect the vacuum to regulator and it goes up to 42

I am not concerned about the running preassure because I am not sure just how accurate the gauge is.

A couple of weeks ago I had the running preassure checked with another gauge and it was 45 with vacuum disconnected.