Lazypitbull

Hi all,
I have a 1988 10ae that has a very strange issue that it runs better when HOT. Here is the details of the car
-stock 13b internals
-replaced the stock turbo with a BNR stage 1
-rewired fuel pump, walbro 255, resistor eliminated
-adjustable fuel pressure regulator
-hks fuel cut defender
- boost and wide band gauges
-the car is otherwise stock
The car starts up great cold, starts great hot when hot, compression numbers are In spec. Idles good and drives good. However under full throttle I find The wideband is reading a solid 10.0 full rich. This is causing performance issues as you might expect, low power and sluggish throttle response.
Here is where things get weird. I drove the car to the store the other day, it was about 85 degrees out. Went it did my business and came out about 15 mins later. The car started right up not problem and I began to drive home. However I noticed right away the car felt better. I decided to give it a 2nd gear pull and the car took off like a bat out of hell. I’m serious that the difference was night and day. I decided to try again from a stop and there was so much power the tires broke loose, which it has never had enough power to do in the past. I was LOVING it so I drove around doing pulls, during the pulls I noticed boost pressure remained constant and unchanged from before holding 10psi. I did notice the wideband was reading closer to 11.1-11.2 during this period of running great compared to before where I was only seeing 10.0 under acceleration. However shortly there after it stop and went back to being slow and showing 10.0 under full throttle.
I am able to recreate this condition any day now by driving the car in a warm day, stopping and shutting the car off for 10-15 min and then taking it for a drive. The car will run great for about 5-10 min then revert back to the slow overly rich situation. I believe this has something to do with temperature? Seems like when the car sits and heat soaks for a bit something changes, after the car “cools down” from driving it changes back.
Here is what I have checked so far:
-metered air intake temps sensor on throttle body elbow(normal)
-Metered intake temperature sensor in airflow meter(normal)
-metered crank angle sensor(normal)

Right now I’m stumped, I think I should check the coolant temp sensor but I’m not sure what one would cause the issue. There is a temp sensor at the bottom of the radiator and one on the engine behind the alternator. Both not easy to access so before tearing into it I wanted to seek some advice. The temp gauge on the dash works fine but I believe that has its own sensor on top of the thermostat housing? The single wire sensor? There is also a sensor on top of the radiator, I understand that is the coolant level sensor?
I call upon the the community, has anyone experience such an issue? What els could I look for? Any help is greatly appreciated. I have the tools and knowledge to fix and check anything you think I should but this one has me stumped at the moment
Greatly Appreciated!
Josh

j9fd3s

iTrader: (3)

so first off the temp sensor for the ECU is the green one on the back of the water pump, this one is a possibility.
coolant level is on top of the radiator
the additional fan switch is on the thermostat housing
the sender for the gauge is under the oil filter,
and the coolant temp switch that turns on the closed loop is in the bottom of the radiator.

i wonder what your fuel pressure is doing when its really hot? you have a lot of fuel for the mods you have. the other thing that i'm thinking of is that the ECU has a bunch of timers in it, and it literally does switch things on (fuel pressure solenoid) for up to a couple of minutes on a hot start

Lazypitbull

Ok this is good info. I’m going to pull out the green temp sender for the ECU and test it per the factory service manual. I need a little more information on the sensor at the bottom of the radiator. What is its function? Sound like it’s a simple switch that tells the ecu to change the fueling? Might that be the issue??
I agree I have plenty of fuel mods and no real way to tune it, that will come later. I prefer to run rich than lean. You mentioned a fuel pressure solenoid? Was that part of the solenoid rack? I forgot to mention I have a full emissions delete so all that was removed

Lazypitbull

Ok all after much diagnosis I have found and resolved the issue of the car running better HOT after heat soaking. The problem was with the throttle body thermowax. The previous owner claimed to have deleted it but he lied. It was still installed but the water hose was cap off. So what was happening was when the car sat and heat soaked the thermowax would allow the secondary butterflies in the throttle body to open. Under any other conditions since there was no coolant flowing threw it it never opened.
To resolve the issue I did the throttle body mod to remove the butterflies. I’m rocking and rolling now! She pulls HARD at 10psi! Woohoo

mazdaverx713b

iTrader: (91)

Have you added your 10AE's vin to the 10AE registry here at the top of the 2nd gen section? I didn't see you on the list.