help with sohc 4.6, it starts like its carb'd

riptide · Jul 2, 2010

Hi my 2003 sohc GT starts hard or only with starting fluid. It will barely run for 10 seconds or so then smooths out, if you try to gas it, it will bog out. Let it warm up and the car runs fine. weird, its not throwing any codes///////any ideas? thanks steven

03 Mustang gT · Jul 2, 2010

check for vacuum leak?

wmburns · Jul 2, 2010

Start first by checking your fuses. Best to check all of them. But esp F2.8 in the central junction box (CJB).

Look at the coolant temperature sensor. Are the wires intact and the connected? Does the temperature guage work?

Next test for a bad IAC. Crack the throttle half way open (not all the way). Does this improve starting? If so, the IAC is bad.

Next, check for fuel pressure leak down. Cycle the key on/off several times without starting. Then start. Does this improve starting? If so, suspect a bad fuel pump or leaky fuel injector.

Check for a bad MAF. Disconnect the MAF electrical connector. Does this improve starting? If so, suspect a bad MAF. This works because the PCM uses default values to replace the missing MAF data.

Not a bad idea to clean the MAF. Use cleaner designed for the purpose. The MAF is delicate and easy to damage.

riptide · Jul 3, 2010

Thank tried the 1/2 throttle ans the MAF disconnect to no avail, alewadt replaced the IAC............keep trying I guess. Steven

nyuk98gt · Jul 3, 2010

riptide:

In addition to the excellent advice given my Mr. Burns (not Homer's boss), the fuel rail pressure sensor (FRPS) might be kaput. If you hit the rev limiter then the FRPS might can be damaged.

Throttle position sensor or fuel pump are a couple of other things that you might check out. One fellow found the 1" plug on the underside of the intake manifold (at the back/near the firewall) had blown out. This would affect engine operation over the whole RPM range so the hole in the intake is not a likely case.

HTH,

Chris

wmburns · Jul 3, 2010

riptide said:
Thank tried the 1/2 throttle ans the MAF disconnect to no avail, alewadt replaced the IAC............keep trying I guess. Steven

Did you check the fuses? If so, the other easier things are likely ruled out.

Test the fuel pressure. Could be bad regulator (1996-1998), FPDM (1999-2004), Fuel pressure sensor, or fuel pump.

JerseyTrueBlue · Jul 4, 2010

Same post on 2 forums, how many responses do you need?

Deleted member 38176 · Jul 4, 2010

JerseyTrueBlue said:
Same post on 2 forums, how many responses do you need?

Really bro? Are you being serious or just need to up your post count? The more responses the better, no matter the number of forums. Im sure you'd be doing the same thing if you needed serious advice

wmburns · Jul 4, 2010

Nightfire said:
Really bro? Are you being serious or just need to up your post count? The more responses the better, no matter the number of forums. Im sure you'd be doing the same thing if you needed serious advice

OK, but it would be nice if the OP actually did all of the tests and posted the results.

Maxpowers · Jul 4, 2010

Is it just me or is starting fluid horrible for cars without an iron block?

trinity_gt · Jul 4, 2010

It's just you.

There's nothing particularly powerfully explosive about starting fluid. It is just a combustible mix of stuff like ether and propane but the key is that vaporizes under just about any condition -- even extreme cold which is when it's typically used -- and it's easy to ignite. Even a weak spark on an engine cranking slowly will light the vapor under conditions when gasoline isn't atomizing nicely (e.g. it's -30oC) and the battery is dying...

It certainly won't hurt an engine unless there's a ton of it in the intake manifold and the engine backfires...

Maxpowers · Jul 4, 2010

trinity_gt said:
It's just you.

There's nothing particularly powerfully explosive about starting fluid. It is just a combustible mix of stuff like ether and propane but the key is that vaporizes under just about any condition -- even extreme cold which is when it's typically used -- and it's easy to ignite. Even a weak spark on an engine cranking slowly will light the vapor under conditions when gasoline isn't atomizing nicely (e.g. it's -30oC) and the battery is dying...

It certainly won't hurt an engine unless there's a ton of it in the intake manifold and the engine backfires...

There's been multiple debates on starting fluid for years. Most people say that it will wash away the oil and destroy your rings. Search around and you will find a debate about it on almost every automotive forum.

riptide · Jul 4, 2010

tried the FRPS with a friends , same result. guess I'll keep trying , thanks for all teh responses......Steven

trinity_gt · Jul 4, 2010

Maxpowers said:
There's been multiple debates on starting fluid for years. Most people say that it will wash away the oil and destroy your rings. Search around and you will find a debate about it on almost every automotive forum.

A couple of points:

First, your question regarded the use of the stuff on engines lacking an iron block, if I recall correctly. The issue of cylinder washdown and accelerated ring wear would be independent of the block material. With certain exceptions, most aluminum-block engines run cylinder liners anyway, giving wear characteristics comparable to iron.

Second, how someone possibly delivers enough starting fluid to wash down the cylinder walls is anyone's guess. The stuff usually comes in a mid-sized aerosol can and leaves the can atomized already. You're basically spraying vapour into the intake. It's certainly not going to be as much of a solvent action within the engine as cold-start enrichment typically provided by either an EFI system or by an old-fashioned choke. And when you do spray the stuff, you're not expected to run the engine on it for more than a second or two. It's quick start, after all.

Anyway, needless to say I don't buy the "wash the oil off the cylinder walls" hype. The biggest concern I'd have is an intake backfire which could yield results akin to a nitrous backfire. A backfire could crack or more severely rapidly-disassemble a plastic intake which was never intended to carry combustible mixtures in port-injected applications.

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