ok, i really can imagine, theres a thread about that, but i couldn't find it with the search engine, if so, links to threads are appreciated

Sometimes i have a hard start issue with the MAP TPI in my 91 Caprice.

When the engine is cold, it always starts quickly and perfect. Mostly when warm too - but sometimes when it's warm, the starter cranks the engine about 3 - 4 revs before it starts, then when it starts, its not starting quickly, but takes some ignitions while the starter is still active, to keep it alive by itself

What i have: old style MAF TPI on a stock 5.7L TBI engine (L05), but running with Painless Harness and 7730 ECM (so now it's MAP), all electric TPI parts new (sensors, Fuel Pump, Relays, even injectors and pressure regulator)


May someone put me in the right direction, where i should start my search for the culprit. It's hard to find a issue, that happens only under specific conditions...

 

Advance baseline timing a few degrees or install a remote starter solenoid to move the solenoid from high exhaust temps, like I did. Remote solenoids are a lot easier than you'd think. Bought mine at summit for $20 or so.

 

why that? my starter turns fine, even when hot, the problem is only that the engine doesn't start fast enough

since it doesn't smell from gas, i guess it's not firing the injectors when the issue occurs - i already tried to find that out, but when i had a noid-light plugged in, everything ran just fine

 

Any codes ? How is the fuel preasure when cranking ? got a noid light ? They are cheap to buy and , can tell you if they are getting a signal . Is there a chance the IAC is sticky and doesn;t move to well ?

 

no codes

fuel pressure is always around 41 psi

of course, but i guess it should be ok, it's a new one... how can i verify this?

i have many of them... but always when i did a test with noid-lights, the problem didn't occur; like i said, mostly it starts perfect

 

gotta get into the prom stuff and diagnoseing stuff. So you can read stuff like knock counts , IAC steps , etc .

How long does it hold the 41 psi for after the key is off ?

 

i'm already in there ;-) but in the DIY PROM forum we decided, that my start-issue is not a software-problem, so i should fix the hardware prob before i start change settings in the PROM

one time i scanned the ALDL stream while the issue occurred, the only thing i saw there, was that the IAC steps value were at the same position like at every else start

i haven't tried it too long, but the few minutes i had the gauge installed it kept staying at 40 psi


exist noid-lights, which can be connected TOGETHER with the injector? i want to try it with noid-lights at both banks, but if i unplug two injectors it's possible that it get another hard start problem because of two missing injectors...

 

do you know if your timing chain is off/loose?

i bumped timing to 12 degrees initial, and it cranks right up, compared to 6/8 i had previously

also make sure the throttle body area is cleaned from carbon, and make sure your plugs/cap/rotor are good

it could be possible that you also have a weak/lame coil

i noticed an improvement with the msd coil, as well as adding the 6a box, and then more when i bumped the timing

 

i don't know for sure since i didn't opened the engine, but i bought the engine as a GMPP complete new crate engine only 5K miles ago, so i think i can eliminate that

did you only set the distributor to 12°, or did you change the initial spark advance value in the PROM too? if you didn't change the value, you have 6° more of total advance, that would be fatal in my case, since i'm using the S_AUJP as base, but had to tune the timing tables by myself, since the L05 engine doesn't allow as much advance as a real TPI engine

the TB is absolutely clean and not worn out, the only thing i could imagine as the culprit is the distributor. It's a remanufactured one from S&P, so all electronic parts are new and the rest is very clean, but maybe they did something wrong or the old one they used had a indistinguishable damage - if the ECM doesn't get a crank trigger signal from the distributor, it wouldn't ire the injectors, right? is there a way to check the distributor for that signal?

ok, that i will check, i have some other coils i can use for testing