Starting Problem

[ptstew]

I installed a 1993 Cobra intake manifold on my stock 1991 Mustang engine. I also installed a 70mm BBK throttle body and new 19# injectors. I kept the stock ECM, idle control valve, EGR valve and 55mm 19# MAF. The engine is very hard to start especially when warm. The throttle must be varied and it finally fires after 5-10 seconds of cranking. It acts a bit like a flooded carbureted engine. Once started it runs smoothly and I have a steady 18 hg of vacuum at idle. Timing is 14° advanced. Is starting being affected by the fact that the MAF is so much smaller than the throttle body?

[CraigS]

I am thinking the idle control valve isn't opening while cranking.

[davekp]

I'd put in a larger MAF- even if that is not the issue, the system components are not well balanced. I did a very similar change and used a MAF from Advance Auto, part no.74-9508. You will have to get an adapter and some hose pieces, and a larger diameter air cleaner.

[Jeff Kleiner]

What is your TPS voltage set to? I go for .95 at idle.

Jeff

[ptstew]

If TPS is the throttle position sensor mounted atop the throttle body, I’m using the one that came with the new BBK unit. How do you check/set it’s voltage?

[Boydster]

Here ya go... setting TPS 86-04 Mustang (https://lmr.com/products/Mustang-Throttle-Position-Sensor-TPS-Install-Adjust)

[ptstew]

TPS voltage is ~0.95 to 4.7 on an analog meter.

[Big Blocker]

While the video referenced above is spot on for voltage adjustment, it doesn't address the throttle plate position. Since you installed a new TB (I'm assuming right out of the box), did you go thru the throttle plate adjustment procedure? once you have done that, then you can set your TPS to the recommended .95-.97 volts, using the videos process.

here's the step-by-step:

According to my ford fuel injection manual.....625-725 rpm is base idle (non Ford lettered cammed cars) - closer to 900 rpm if non-stock cam in installed.

Clear keep alive memory in EEC (pull negative battery terminal for 5 mins and reattach)

Engine off, install feeler gauge 0.025 between throttle plate idle stop screw and throttle lever

run engine @ 2500 for 30 seconds. Release throttle back to idle position.

If idle is too low, turn idle screw to adjust rpm to 650-725 (see above comment).

If rpm still too high, check for vacuum leaks. If still too low adjust idle up with stop screw.

Recheck idle to 650-725 rpm. Turn stop screw only clockwise. If you turn counter clockwise, throttle plate may stick.

Remove feeler gauge. Key off, restart, idle for 2 minutes.

Engine off, disconnect negative bat terminal for 10 minutes

Run KOEO self test for proper TPS output codes.

Start engine. Run 2 minutes. Goose engine, return to idle. Gently press accelerator. Return to idle. Recheck to verify that idle problem is cured and rpm is within spec.

Doc

[ptstew]

Thanks, Doc. I have not completed the process you describe, but will. Unfortunately, engine has gone from hard start to no start. I am still trying to get time to figure out why. The couple of times I initially got it started it ran great in garage on jack stands at all rpms up to about 3,000. It idled smoothly at 700, same as before and fully warmed up. I turned it off with the key and it hasn’t started since. I have spark from distributor at crank. I plan to try starting it with ether and going from there. Unfortunately, I replaced a bunch of stuff during the install in addition to the TB (injectors, fuel pressure regulator, air charge and engine coolant temperature sensors in lower manifold) any of which could be bad. The stuff in the stock engine wasn’t bad, just 28 years old and it seemed time.