The Warmer it gets outside, the rougher my 302 runs
 

I have been chasing this for quite a while now. The hotter it gets outside, the rougher my 93, 302 runs, and power starts to fall off. On a manual 4wd Supercab. Cool mornings, runs much better. New plugs, a couple years on wires, new cap and rotor, new fuel filter/air filter. Timing is 10b with spout removed. No codes. No vacuum leak that I can find anyway. Vacuum is steady at idle, and doesn't seem to fluctuate. Higher rpm, same. Steady.

I do have a bad check valve forward tank, rear fills front tank when used. (that's pretty sweet. :-roll)

It has been doing this for over a year. I moved from 5500 feet to 1500 fee in altitude a few years back, and it has not really run right since. But I should be within PCM range. (?) Anyone else run into this? I replaced the map sensor, no effect. TPS tests good. Going to clean our IAC today, and try to verify EGR operation. There is 527 pages in this forum, and I might have missed something, but I tried to search it a couple ways. If this was ever addressed before, I can't find it. Any ideas would be appreciated.

You may want to test the ECT sensor. It's commonly overlooked in diagnosis. You can test it with a DVOM and compare your resistance #'s with cold vs. hot. If you need a few #'s from the Haynes manual, I will post them. Also check the IAT sensor as well. It sits on the lower intake, driver side, close to the front of the engine. I have seen/heard that these fail without any CEL.

You may want to check the operation of the O2 sensor too. It sounds like when the truck enters closed loop "that is where it's taking info from sensor's and then adjust for performance and good drivability", your truck begins to falter. A failing sensor is a good guess since it hasn't thrown a code to completely say it's operating under a fixed value until the condition is corrected. 1 downside of the OBD-1 system is that if 1 sensor fails, it can create a dominoe effect, resulting in what "appears" like other sensors are failing, when really the "1" sensor was bad.

Hope this helps.

EDIT: Do you have the scanner to check codes with? If you did, you could get the truck to operating temp, then hook up the scanner, and then perform the "Key on, Engine Running test". This may force the truck to run terrible and thus throw a code finally.

EDIT: When you checked timing, did you also check to see if the timing advanced when you put the Spout connector back in? If it isn't advancing, I could see that causing a problem as well.

yep.. no codes, KOEO or KOER. Well, code 11's.

I will find the range for the IAT sensor. Maybe it failed in range, and is just stuck there. (electronically) You would think I would have checked that already, based on symptoms, but I think that I overlooked it, because I have no codes.

Good idea. Also, both the IAT and the ECT operate on the same resistance variables. Be sure to check both while cold and then @ operating temp. You want to look @ my post again regarding the "Spout" connector.

what plugs are you running? does the motor appear to get up to proper operating temp? if you havent done so already, replace the Tstat with a new 195* unit.

ASF-42c spark plug. I have played with other plugs, but it only seems to like the originals. Gapped to .055"

Seems to get up to temp fine, although it takes it a while, compared to the wife's aluminum block explorer. :) I just use the dash gauge for that, and it is where it always has been.

It will be a day or two before I can check the IAT and ECT. Busy after work for a day or two.

I am also having issues, with the Idle Air Control. Seems that high idle is higher than it should be, but not high enough to pull a code. And, it doesn't have that deceleration snap that it should, in that 3 or 4 seconds after letting off the gas. I am thinking I am getting leakage around the plunger. After cleaning it yesterday, i can blow air from both ports, while it is de-energized, and in my hand. With out being energized, I shouldn't get any air to blow through from the up stream port to the downstream port, should I? I am wondering if air is vacuuming through that.

those plugs are gapped a bit much for only running the stock timing of 10*. they should really be back around .042-.045. you might consider bumping the timing up to 12* if you want to keep that gap.

are you still running the stock tfi coil.

Kemical, I thought most of the earlier V8's had plugs gapped @ .042 - .045? I think it was in later model years the plug gap changed to .052 - .056. I know the decal on my hood of my '92 302 is .052 - .056.

yep, hood and shop manual have .052" to .056" . I tried running at 12 deg, but I get some occasional, but big pre-ignition. So I backed it back off. Definitely had more power, but I am in Oregon too, and fuel here is also 10% ethanol. She doesn't like that crapola very much to start with.

Today, I have my vacuum gauge stuck to the dashboard, so I can watch it. It seems that I have to use way too much throttle, especially this afternoon when it was warmer. And, I get a definite +/- about 5 in. of vacuum fluctuation, rhythmic at about 2 seconds peak to peak, even if I hold the accelerator as steady as I can. It is hunting for something, but no code.

Almost feels like it is running rich, in the warmer air. Good power from stop, but at highway speed, really doggy.


Still Could be the IAT? I don't know how much influence that has in the EEC system.

when you changed the timing did you do it with the spout connector removed? Im running 12 on my 5.8 with no issues so something doesnt sound right. you might run some seafoam thru the system.

i will have to look at my sticker for plug gap, odd yours says so high. and those are copper autolite/motorcraft plugs correct

Yes, with the spout jumper removed. Holds 10 right on the money at all rpms. Spout back in, and timing advances properly, and at rpm. I thought that too, that it wasn't advancing.

i haven't tried the sea foam route. I have never been big on any additives, and i haven't poured anything down the throat in a long time.. the neighbors will love that big cloud... lol But I am willing to try about anything, as I am getting stumped.

I will try that, both fuel side and oil side, since I have a change coming up. I will run some for a while before dumping it. Can't hurt anything. I probably need to meter out the IAT and ECT and see what they show. Have to wait for the weekend to do that.

My Alldata subscription and my underhood sticker all call for the larger gap on my plugs, hence the .055". I do not believe, that these plugs are the coppers though. Just the OEM Autolights.

I appreciate everyone's input, and I am confident, that we will get this figured out... :)

Well, no luck yet. So far, I found these issues. I had a pinhole leak in the throttle body heater hose that completely soaked the TPS and caused all kinds of havoc. Replaced all the heater hose under the hood while I had it drained down. Replaced the TPS, as I didn't trust it anymore, after the bath and subsequent wild RPM fluctuations. .9 volt at throttle closed, and smooth all the way to WOT. So that is working good.

That got me back to the baseline problem that I still have.

I did the SeaFoam route, and as a matter of fact, it did smooth out the idle somewhat. Did not really effect the cruising power loss that I get. (it did do a great job smoothing out my 2006 Explorer though!! )

Replaced all plug wires with Autolight Pro's, and plug inspection looks good.

Cleaned IAC valve. I had an extra MAP sensor on the shelf that I had swapped out a while ago when I thought it was a problem. (Motorcraft) I reinstalled that one, for giggles. Replaced Cap and Rotor. Function test of ERG valve is good by vacuum pump.

No hard or soft codes, and no faults KOEO or KOER.

I still have a power loss at cruise. Acceleration is good. But when I reach cruise, and try to hold it at say 2000 rpm highway, I can feel it losing power and trying to get it back. It is not really bad, but I can sure feel it. Not bucking, but in the background. Sucking fuel I am sure.

I also have recently noticed, that on Deceleration, that it no longer has that hard decelerate after the injectors kick out. Just seems to roll with out going into that stage.

Known problems?
I know that my forward pump shuttle valve is bad, but I am getting about 29 lbs of fuel at the rail.
I have not tested the intake air temp sensor. I have not tested the O2 sensor. Replaced in 2003, about 15000 miles ago. I have not tested the ignition module. (replaced in 2003 also) I was thinking that I was getting hot, and messing up maybe. Causing timing to fluctuate?

Any help from the experts would be appreciated!

Thanks!
Hal

Still no luck. Still have that feeling of bogging down slightly and back normal, in a cycle. I am leaning toward the ICM, since it seems to be heat related.

Any thoughts?

I would investigate this. I'm not sure what a pump shuttle valve is, but I think Ford's spec for fuel pressure is 35-45 psig, so 29 is too low. Your symptoms do seem to indicate insufficient fuel under load. My fuel pump did the same just before it died; seemed to have enough pressure at idle, but under load the engine started to bog down, and even knocked at some point. As it weakened, it just could not keep up the pressure and flow rate under load.

If not the fuel pump, I'm thinking that shuttle valve is obstructing fuel flow.

It occurs to me after re-reading this thread that there may be another cause of the problem. Since you say it's heat related, did you check the TFI module? If yours is bolted to the distributor, it is among the many that suffer over heating. I moved mine recently to avoid the problem:

https://picasaweb.google.com/eycchu/87MustangEngine