C4 question

Guro305 · 10-24-2006, 01:34 AM

Ok, I know I'm a C5 owner but this one is for a friend who has an LT1.

Today on I-95 his car started to ping a couple of times, seemed like it was bogging and then just died. He said the last couple of weeks that sometimes it's been hard starting and when it starts it seems to idle rough. Anyway, he couldn't start his car after it died. He said he can hear the fuel pump and it sounds fine.

I remember having a similar problem like this, not with my 'vette but with my 300zx. It sounds emissions related to me. Maybe stuck open/closed EGR, or bad MAF. Have any of you guys come across this before?

Mekanic · 10-24-2006, 01:53 AM

could be a bad MAF, what grade gas is he using?

Also tell him to check the TPS voltage and fuel pressure.

Guro305 · 10-24-2006, 08:43 AM

Quote:

Originally Posted by Mekanic

could be a bad MAF, what grade gas is he using?

Also tell him to check the TPS voltage and fuel pressure.

93 Octane, Mek'! Yes, yes, these are all things I told him. I told him it sounds to me to be all fuel or emissions related. Doesn't sound like anything detrimental to the engine. Good lookin' out.

Mekanic · 10-24-2006, 09:19 AM

Fuel or emissions is what I'm thinking, fuel pressure, MAF, TPS, fuel filter, etc.

Also, what year and mileage? If all the others check out well...it sounds like it might be opti. Did he wash the engine recently? Wondering the year to know if it had the vented or non-vented opti. Without cap/rotor replacement and inspection, they've been known to go around the 80k mark

If it is his opti, 99% of C4 guys will reccomend he does the water pump at the same time, they crap out too, and since you have to remove the water pump to get to the opti, its the perfect time.

Guro305 · 10-24-2006, 09:26 AM

'94 with around 63K. Ok, not to sound dumb but, what's an opti?

Mekanic · 10-24-2006, 09:36 AM

OH the optispark, the LT1/LT4's answer to a distributor.

It uses 3 optical lpickups that see marks on the end of the camshaft to adjust timing.

it works great.....unless you get it wet... then you are indeed screwed. And since its screwed if it gets wet, the wonderful GM designers mounted it....under the water pump.

Thats why you can't "wash" a LT1/4, just simple green and rags.

But I'd make sure that the fuel pressure primes to 70 PSI before cranking, and the TPS shows .54 volts at idle, as well as cleaning the MAF, and looking for vacuum leaks. Then I'd start looking at opti.

If he washed his engine before it started running rough, you can pretty much eliminate everything and go right to the optispark.

Posted wrong link before http://www.ecklers.com/product.asp?p...dept%5Fid=1285

2Vettes · 10-24-2006, 09:14 PM

Oh, I remember the opti-spark well.....

First hand, just like you said. I washed the engine in my '92 and killed the opti! Tried the hair dryer trick to no avail. Pretty expensive car wash

Once when I had a fouled spark plug it ran really rough similar to what you're describing. But, I was able to start it.

Guro305 · 10-25-2006, 09:18 AM

I asked him if he gave the engine a bath and he said no. He had his car at the shop and the car didn't throw out any codes.

They couldn't find anything wrong with any of the aforementioned parts. The mechanic said all he could think of is that it's the distributor. I told my friend, "uh, they don't have distributors, they have the wonderful opti-spark." He kinda figured that out on his own. Now the car is in pieces in his garage waiting for the part to come in.

Will keep you guys posted.

Guro305 · 10-27-2006, 11:52 PM

YES! It was the Opti-spark. Good call to everyone!!!! Car is running.

Mekanic · 10-28-2006, 12:28 AM

yay! Sorry to hear the problem, but very glad to hear its on the road again!