It's the summer time in AZ, and my car already hates me. Runs and drives almost perfect (with minor hiccups here and there) in the winter time, but as soon as the weather peaks over ~85 those small hiccups become unbearable driving issues.

Without going into too much detail, and writing an essay about all the little crap that happens at certain times etc, I'll just ask a few questions and give brief example.

My main question, which sensors/controls on the engine are adversely affected by hot air? Be it intake air, or ambient temps. My car doesn't run more than a few degrees warmer in the summer than it does in the winter. It's the hot summer air that I know is causing issues. My first thoughts are the AFM. But if it's not causing problems at lower temps, it seems like it would be hard to test its functionality at higher temps. Make sense?

What else can cause problems when its hot out? Not sure if it's a coincidence, but if I shut the car off without letting it fully cool, the problems are amplified (from heat soak I imagine).

And a brief explanation of the main problem would be surging during acceleration between 0-4 lbs of boost. The car leans out for a quick moment every second or two until the secondaries kick in (which cause a large bucking motion), then it smooths out.

I believe my wastegate is sticking also, because when the car fully warms up or heat soaks, I hit a wall at 5 psi, and not matter how hard I mash the pedal, it won't go any higher. Nomal boost for me is 9 psi. But I fail to see how that could make the rest of the car run like shizzle.

I've cleaned grounds, replaced grounds, added grounds, with no success. The only thing I haven't tried is cutting the grounds at the ECU and bolting them to the floor. And I'm not sure which ground to do that to (as there are multiple).

And there you have it, I've written an essay anyway. This problem has been plaguing me off and on since I bought the car last year. The winter months merely masked the issue I guess.

Any advice or help offered would most certainly help me regain some sanity. Thanks!

Any locals want to come give it a shot? lol

 

there is an air temp sensor in the AFM and @ the intercooler elbow, you may wanna check these, just to make sure they are telling the ECU its 100F when its 100F....

what mods are done to the car? i've had surging@ cruise, and i think its caused by the stock ECU+ big exhaust, and instead of cycling around 14.7:1, the engine is turning on and off.

 

3 inch exhaust, 720 secondaries, rtek 1.7.

I've replaced the sensor on the TB elbow, but it was another used sensor, so it could have been bad too I suppose.

I've been suspecting the AFM, but I'm not sure how to test it if it functions normally without it being hot..

Your surging at cruise comment reminded me that if I turn the A/C on, it will start to "stutter" during cruise too. Almost like its missing or something at random. Sort of hard to feel on bumpy roads, but on the freeways, it can be very noticeable.

 

You seem to have a boost control problem. What controller are you using?

One thing to check is the air temp sensor in the throttle body elbow. Seems like it would throw a code, but you can remove it and check the cal resistance. (j9fd3s beat me to this)

Another heat related problem is the fuel pump resistor relay. While that doesn't sound like your issue, they really screw-up the fuel pump voltage output when it overheats. The catch is that to fix it (bypass it), you essentially need an controllable ECU.

 

I'm up for trying anything.. But the fuel pump relay, how would I tell if that was the issue?

 

One step at a time. Understand that the diagnosis is just a process of elimination starting with the most likely problem.

1.Can you find someone to borrow another AFM from, to test it? Will the rtek allow you to see the sensor measured temp?

2. Sounds like you're using the stock TPS - have you adjusted it lately? The TPS is susceptible to temp drift.

3. The best way to diagnose the fuel resistor relay is to attach a fuel pressure gage and see how it varies while you drive,

 

^^Thats a start. However, I don't know anyone local with an N370 AFM I can borrow , does the FSM describe ways to test it?

TPS has been adjusted recently. Ran a new full and narrow range wire for it too (there was some resistance in the factory wiring).

I have a fuel pressure gauge (hand held), but it uses a schroeder (sp?) valve, so I need to locate an adapter I can put in my fuel line... Or spend the money on a permanently mounted one from prosport...

 

my F guage had a shraeder on the end of the hose i just cut it off put a T fitting on there and then took the line from fuel pump to engine and connec that in line with the T and another short hose back to the engine.
and i have a N A so no N370 AFM

 

have u tried cleaning your engine grounds?

 

i think it would only throw a code if it was shorted or open, if its just way off the ecu would probably just believe it.

i do like the TPS thing, i plan to set mine at least once in the winter and once in the summer, engine needs to be HOT when you set the tps too.

 

A car with boostcreep will do so less or not at all in hotter temps...

 

I'm a master of setting my TPS. Even built a test pipe so I could monitor it with the engine running at different RPM's.

Can you clarify what you mean?

I've cleaned (on top if the housing, and the set that runs to the IC mounts) a few of the engine grounds, and even ran extra's.

 

the dealership i used to work at had one of those.

 

Are you asking what boostcreep is? Or why it's exacerbated by cold intake air temps?

 

Why its exacerbated that much by cold intake temps?

 

cold air=more power. more power=more exhaust. more exhaust=more boost, more boost... boost creep.

 

So ~10 degrees difference is enough to lower boost levels by almost 5 psi?

 

That's a big drop in boosst no doubt. But heat soaking the stock TMIC can have a dramatic effect on power and will all but eliminate boostcreep...

 

Hmm... never realized it would be that bad. Would it be a bad idea to put a wastegate on that opens a little later?

 

Wastegates dont open early or late. They open on pressure..
if you use a different actuator with stiffer spring, you will always get more boost and need to modify more stuff to make sure the engine does not pop.

But this will not fix your problem, because even then you will get less boost when hot!
You will need to get lower intake temps to tackle this problem

 

Ok. Lets not get too far off on a tangent. The big problem here isn't the lowered boost pressure. I'm more concerned about the fueling issue I've been having.