I generally start off with a mod list before I describe my problem to give people a better idea of what Im dealing with exactly so here it goes.

94 chassis
street port motor
all plugs are 9s
magnecore wires
hks ignition
hks fmic
gt4088 journal bearing turbo
greddy manifold
catless 3" trust exhaust
fluidyne radiator
2 spal fans
550cc primary injectors
1680 "blue top" secondaries on a KG PARTS rail
Walbro 255 fuel pump
Aeromotive FPR set to a base pressure of 42psi
P/S, air pump, and A/C deleted
Apex'i Power FC with a base map made in datalogit from another local owner.


This is a problem thats developed recently. Once the car gets warmed up, it wont start above 70*C. It was starting up just fine when at normal temperature about a month ago and has been driven daily all summer. The car DID NOT overheat and isnt losing coolant so that almost rules out coolant seals. I just spent a day tearing apart the upper intake manifold, throttle body, fuel rails, and replaced all the vac lines with the job.

The intake air temperature sensor tested with a resistance within factory spec
throttle position sensor is adjusted right where it should be
The throttle body is free of leaks and adjusted properly

Does anyone have any ideas on what could be the cause of this? Everything looks fine in the sensor/switch check menu on the PFC and it runs great while at normal operating temp. Once you shut it off, it doesnt want to start back up until it cools off. It will fire every so often but wont get enough combustion to start up. Ive tried holding the gas pedal all the way down to try to de-flood it because I thought that was maybe the cause of the no start. Didnt help at all.

Under the water temp correction menu, I havent changed anything from the day it was set up. cranking time is 10.3ms at +80 if anyone is wondering.

 

You can try reducing the amount of fuel injected under warm conditions. On my FC, I only use an injector pulse-width of 8ms for warm to hot temperatures, and I could probably reduce it further. I would also do a flood-clearing procedure by disabling fuel injection (typically by pulling a fuse) before cranking the engine over.

 

Fuel injection disables under wide open throttle while cranking.

I tried messing with the pulse width a little more today. Going from 10.3 to 12.4ms seemed to help a little bit. Ive decided that we really need to get a wideband in it also. I took it down the road and saw some very disturbing counts of knock.

 

Hate to ask, but what's your compression at? I had this same problem, and after checking my compression, i had around 70psi.....it ended up being my good ol' trusty apex seals and now i'm in the middle of a rebuild. You can also check your injectors. A leaky injector will also sometimes be the problem as well.

 

You want to be tuned to your mods especially when you have a ported motor and big single turbo. The base map in the PFC won't cut it.

Time for a compression test.

Also double check your Oil Metering Pump sensor in the PFC sensor check.

 

I finally got time to run a compression test on it. Were getting about 73psi on each face for both rotors. Its my understanding that those readings are pretty good for a street port.

One thing that I did remember about this whole situation was kind of interesting. While my DSM was torn apart a while back, I loaned the owner my battery. He drove around on it for a couple months and everything was fine. It seemed like once I got my car finished, he was the one having problems. We just kinda wrote it off as one of those "if its not one car, its the other" things.

While doing the compression test, the motor wasnt spinning up too quickly at all. I grabbed my car and gave him a little boost to do the test. Turns out, his battery is a little riding lawnmower sized thing. He never said much about having to wait for his battery to recover during his starting issues. Makes sense now. As soon as he gets up, were going over to the parts store and sticking a brand new optima red top in there.

For anyone thats wondering why my compression numbers are so low, I currently reside at 4700+ ft. He talked to another FD owner in a near by city(a bit lower elevation) and he was getting similar results. Now Im curious as to what my brother gets on a compression test at his elevation. He sits around 6700 ft. so I would imagine his is similar to the results I came up with because hes on a stock port.

 

The base map that was uploaded came from another local with a very similar setup. The only thing that was different was he has a slightly smaller turbo. Other than that, the setups match and have only changed a tiny bit in the timing tables for the final tune. It was all uploaded via datalogit.

 

I'm not an expert on compression tests but 73 PSI on each rotor face seems like an odd reading. Hopefully someone else will comment on that.

Did you hold down the shrader valve while doing the compression test?

Their is a how-to in the FAQ threads.

 

I'm not sure what access you have in newbie land, but here are some threads on the subject:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/hot-starting-issues-what-check-924171/
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/hard-start-long-start-discussion-modified-setups-897249/

Something from one of those threads:

 

73 psi sounds blown to me ideal is 120 and below 90 is rebuild I don't think elevation makes that much of a difference

 

Now that we have the new battery in, Im sure the results of the compression test were affected by a lower cranking speed even with another car hooked up to give the battery a little boost.

Sideo, there is an altitude correction that you can look at in the factory service manual. Take a look at something describing altitude vs. density. Its definitely enough to make a note of.