Car runs like POO especially when HOT outside

95 park ave. noticed this last summer. it doesnt have the power or acceleration that it used too. When it is hot out side, it runs like junk. going up hills, it feels like there s a dead spot where it doesnt want to accelerate.

I changed the TPS with no effect. It has a new O2 sensor, new plugs and wires too. It has a rebuilt motor in it with 18000 miles on it.

When it gets hot outside (over 90 degrees) the problem is WAY MORE pronounced. when it is cool out, it runs halfway decent.

Going up a hill (not even that steep) this morning at 75 mph and it downshifted to make it. the ac vents always change to defrost mode during this problem indicating lack of engine vacuum.

Please help. Im about to go to the dealer and pay for their diagnosis.

Fuel pressure maybe??? the car has 207,000 on it (tranny rebuilt sometime before I got it. engine rebuilt 18000 miles ago.

I'd start with a engine vacuum check first, then a compression test, which the vacuum test will probably point you in that direction if my thinking of what' swrong is correct.

Strongly suggest keeping it simple here, I believe it's a mechanical failure and not PCM related.

I bought a fuel pressure tester last night and got some readings in my driveway. I had 48 psi at key turn on (no start) and the spec is 48-55 for my K code engine. at idle it is around 41 psi. These seem in spec although on the low side.

Also, at the key on/no start test, the pressure leaked down from 48 down to around 40 after a couple of minutes. I would assume this is bad but I cant tell whats causing it because I dont have the fuel rail shut off adapters that the service manual call out. They shut off either the supply or the return (or both) to find out where the pressure loss is from.

Can you buy these anywhere?

I'll do a vacuum test and a compression test tonight.

I use small vise grips (carefully) on the rubber hose section of the return, it works and just as effective.

cool Im gonna try that tonight too (watch me puncture a line).

Yeah, just be careful, use just enough tension on the grips to pinch the hose, it's pretty thick and shoudn't snap on ya.

Looks like your fuel pressure is OK and it is normal to leak down over a few minutes. If you have low engine vacuum, you could have a valve leaking. Intake or exhaust on one or several cylinders. Next step would be to do a leak down test. That will tell you what cylinder is leaking and where, if it is done correctly.

ok, I have a leak down tester as well. (never used it but i have one) I can try and do that test tonight too.... I better buy some beer on the way home. i think its gonna be a loooooong night.

ok, I have a leak down tester as well. (never used it but i have one) I can try and do that test tonight too.... I better buy some beer on the way home. i think its gonna be a loooooong night.

Yeah, but it's summer, now's the time.

Still say, do a vacuum check first, this will give you a ball park idea on which way or test to go next.

On the fuel pressure test there's a percentage applied to the amount of loss over a set time that eludes me right now. Honeslty tho, I don't think you're dealing with a fuel issue here. You could hook up the guage and try to cause the problem to occur and see where the pressure is, but I don't think that's it.

ok, here are my results so far.

At idle, the engine vacuum is 18" (which seems okay doesnt it?). If i rev it up, it momentarily drops to 10" or 4" (depending on how fast and how far I open the throttle) and then it goes up to 22" and back down to 18".

I did a compression test and the numbers were
on a 4 puff test:
1 136 2 130
3 138 4 130
5 134 6 135

on max compression (crank until it stops rising) I get:

1 158 2 145
3 160 4 154
5 162 6 158

So cylinder 2 is low but still within 20% of the highest. What is normal compression and vacuum on these cars?

I didnt get to do a leak down test becasue the fitting on my leak down tester didnt match my air hose and it was REALLY hot last night and I quit early.

what do you think?

vacuum sounds good (except) looks you have a problem with engine sealing between 2 & 4.

Any signs of mixing between the coolant and oil, or fuel in the oil?

nothing that I have seen. and thats a pretty obvious sign.

what kind of compression numbers do these cars usually run?

The rest of the cylinders look about normal. Anytime there is a lower number between two adjacent cylinders is a fair indication of sealing prob. mostly head gaskets, which on these motors they and the intake manifold are common to require replacement every 30 -50 K dependant on how well the upkeep of the engine is.

Looking at the numbers again, that whole bank is lower than the other, wonder if the gasket wasn't seated right during the build. Or, but less likely, the piston rings aren't sealing on that side. But if it's causing enough problems that engine does not produce enough vacuum there should be some idication of an internal or external leak?

No other signs of problems though?

you guys are gonna be mad but i think i found something today. I was reviewing my records and noticed that I hadnt changed my air cleaner in a while. I thought i changed it when i put the new motor in but i didnt.

I changed it last night and today the car is running a whole lot better. its about 89 degrees out so the real test will be when i go home tonight but at first blush, it was the culprit.

I am such a dork. I looked at the aircleaner earlier and it was still white so i figured it was good. lots of dust i guess clogged the pores.

I'll post again when im sure thats what it was.

the vents changing to defrost is still happening although not mearly as bad.

i'll post updates.

(note to self: what an idiot!!!)

That's too funny. Would explain alot.

You ultimatley have a problem brewing in the one bank tho, probably loose or not seated properly gasket.

hey wright, you were right on the money. after changing the air filter, it helped lot but the problem resurfaced later on.

Turns out IT WAS THE FUEL PUMP!!!! 2 years later and the problem is fianally solved

I had checked the pressure at idle and it was 45 psi but apparently, when it gets hot there isnt enough gusto when the engine demands it. I took the car to a shop and told them everything I diud from changing vacuum lines to changing the vacuum resevoir (which did leak btw) to checking the fuel pressure, compression testing, tps changing etc.

the shop asked if I tried pinching off the return line for the fuel and I said no. they said the fuel pressure sould spike and if it doesnt its the fuel pump. I was hesitant to believe but sure enough, they changed it and it works like a champ. THIS IS WHAT YOU SUGGESTED AND I NEVER DID IT for fear Id break a line.

They did it and said it was a bad pump. changed it and im good to go

2 years later and its solved. hip hip horray

I'll recheck them again. my compression guage was acting funny when I took those numbers. at first 2 and 4 cylinders were higher the first time I took them (they were around 150) then when I tested the #6 it started acting wierd and only got to 130 so i rechecked 2 and 4 and they were weird too- at 130. so my guage may have freaked out on me..... no reason they would suddenly be lower than the original readings by a lot. (i did 1 , 3 and 5 first then I did 2 ,4 and 6)

We appreciate the follow-up; however, it would be better to start a new thread and link to this one. Posting in Closed or Outdated Threads (http://www.automotiveforums.com/vbulletin/showthread.php?t=635164)

Thanks for your cooperation.

http://img326.imageshack.us/img326/4093/threadclosedga9.gif