: Noticeable drop in power in warm weather

05-12-11, 05:49 PM
My 98 Deville lives up here in Wisconsin so it is just starting to get warm here(it's like 84 degrees today) and I've noticed that my engine is more sluggish than in cold weather. In 45~50 degree weather I can chirp my tires at every stop but now when I stomp on the gas it feels like the engine isn't running in all 8 cylinders until about 3000~3500 rpm. Any ideas? My spark plugs are AC Delco about 8 months old, the wires are about 2 years old, no codes besides the "check gas cap P0440" message so I think I need a new gas cap. The car is approaching 180k miles so am I just asking too much for an old car? A long time ago I was told that my fuel injectors are seeping gas but I've been driving it as-is for a few years now, but the drop off in power during warm weather is new this time.

05-12-11, 10:42 PM
P0440 refers to an EVAP system fault - most often evidenced by a loose gas cap, BUT it can be anything from a faulty EVAP solenoid/vacuum line at the rear fuel rail area to the charcoal canister under the driver's side rear door frame area to the fuel tank vent system to the canister. Any vacuum leak in that system will cause sluggish operation and maybe set mixture (lean) code(s).

ANY fuel injector leakage or faulty operation is performance-robbing as well as dangerous.

05-13-11, 04:22 PM
I did buy a set of good used injectors from another 98 deville with 87000 miles and another set of injectors/rails that has unknown history a few years ago, I never actually installed them because this is my only car and I don't want to mess something up. It looks like a job that'll take about an hour and a half if I do it myself and I have the tools to do so. I wanted to just let a mechanic do it but they're trying to charge me like 300~400 dollars for labor so no thanks, plus since I'm using my parts they can't give me a guarantee that my car will come back running like before. Dealership is trying to charge me $1200 to replace with new injectors.

I do have the 3-book service manual for my car but to be honest I have no idea how to find things in it :rolleyes: page reference didn't make sense to me.

Can you guys give me some tips on replacing the injectors?

05-13-11, 06:00 PM
Remove the engine cover. With a rag under the fuel rail Schrader test port, bleed off the fuel pressure - about an ounce or so. Remove the injector electrical connectors - safety locks and squeeze pins. Remove the rail hold-down nuts. The right rear may be a bear on some cars. Either use a fuel line disconnect tool set from NAPA or carefully lift the rail + injectors (still attached to the fuel lines) out of the manifold. Release the individual injector retainer clips and pull the injector from the rail - repeat 7 more times. Reverse for install, using a smear of oil on the injector O-rings.

BEFORE you replace injectors (they're very reliable, regardless of what the car parts stores tell you), use a mechanics stethoscope to listen to each injector at idle - a nice, steady rhythmic tick, tick, tick, tick ??? The injector is most likely OK. Try running a 20 oz. jug of Chevron TECHRON through the engine - with a fill-up of 93 octane Shell, Texaco, or Chevron. That's a HD fuel system cleaner.

05-13-11, 06:53 PM
FWIW, if the injector is actually "plugged up", no fuel system cleaner or fuel is gonna take care of it. If you've ever seen an injector with a crusted up pintle and a gummed up injector filter, it's a no brainer - there is just no way it's gonna happen with some cleaner diluted into 20 gallons. You could soak it directly in parts cleaner and you'd still have to get some agitation action going to remove it. Perhaps that stuff is good for maintaining a clean fuel system, but it will not clean up an already contaminated one.

I'm assuming you were told that the injectors were leaking gas through the valve, into the intake manifold rather than externally on top of the manifold (which should be obvious simply through smell). If your injectors are actually seeping, one of the most apparent symptoms you'll generally experience is hard starting (caused by the excess fuel in the manifold from the injectors bleeding off the fuel pressure after last shutdown.)

To be sure, you could always hook up a pressure gauge, switch the key on and let the fuel pump prime the system. Turn the key off. If the pressure drops in a short period of time, you have a leak at the injectors, fpr, or check valve. If not, your problem likely lies elsewhere.

The OBDII system is pretty sensitive to fuel trim changes and the car would probably have thrown a relevant code by now if the running problem was caused by a fuel balance problem.

05-13-11, 09:40 PM
I Do have a hard start issue and it's a weird one, it's not the FPR(no leak on the nipple, replaced it anyway, didn't change anything) & no codes. 5 years ago a mechanic told me that my fuel trim is stuck at +6 but I disregarded that. Now am I right that if my injectors are seeping gas at the nozzle then with no keys to the ignition no gas or very little will come out of the test port right? For a normal one should it be squirting out like a hose or is it like an overpoured beer?

I have hard starts only after the engine warms up AND it's been sitting for about an hour, it'll crank but to no avail, the starter spins good. Eventually it'll start but it starts faster if I press on the gas pedal all the way down. If I wait for 3+ hours then it starts fine. This hard start problem is much less apparent in winter freezing temperatures but it is worse in warm weather like right now. The funny thing is this started happening right after I put a stereo in this car 4 years ago (it ran rough, check engine light came on, but after like 2 miles of driving the light went away and car ran fine like nothing happened, and it never happened again) so I've always suspected my own wrongdoing. The only thing I can think of is I have a 1/0 power cable with the black factory harness on the passenger-side firewall and it might have snagged something when it went through down by the front passenger's foot. Can you guys tell me what electronics are on the inside of the passenger firewall?

05-14-11, 02:16 PM
Still none of this explains why I lose power in warm weather though, and it wasn't like this the year before.

05-19-11, 03:54 PM
ever clean your butterfly in throttle body? open throttle and use rag with solvent and clean throttlebody throat area. back of butterfly also. i had car that would start great and die right away. within seconds. only when hot. might help you.

05-28-11, 09:31 PM
I clean the TB about once every six months, I just cleaned it about a month ago and I remember it wasn't all that dirty.

05-31-11, 02:05 AM
An off the wall question: are you running your climate control in auto? If yes, the air conditioner compressor may be your problem. In cooler weather the compressor doesn't run, but in warmer weather it will run and rob you of power.

05-31-11, 11:26 AM
But hardly enough to be noticeable.

05-31-11, 02:17 PM
Try ohm checking the Injectors, see what your findings are, do them when cold and hot.


06-27-11, 10:44 AM
Most cars produdce less power in warmer weather! Warm air is less dense than cold air, thus the warm air has less oxygen in than cold air of the same volume. Less oxygen means less fuel and less power.


06-27-11, 11:21 AM
...............but remember that modern PCM controlled air/fuel mixtures compensate for air density, barometric pressure and intake air temperature................

06-27-11, 11:49 AM
Also remember that the seat of the pants dyno is not likely sensitive enough to pick up the difference.