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Darkness
01-08-2010, 03:47 AM
It's a 3.4L from a 98 Transport Montana, any help will be appreciate. Thanx in advance. If this is not suitable in General section, Admin please move this thread.

Here's the story:
Last week my wife's van suddenly acted up at one nite. It can't rev over 3000rpm. It doesn't matter at any speed or gear, it just quit at 3k rpm. When it reach 3k rpm, it's choking and act like fuel is cutting off.

Next morning, try to start the engine and do some diagnoses. It cranked but not start. IT doesn't have any kinda SES light or code. I followed GM SI manual to diagnose the problem and here's what happened:

The MAP sensor read 104 kPa. Then I unplug the MAF sensor and it won't start. I replaced the MAP sensor, same thing. I've fuel pressure at the fuel rail with 42psi. I checked all 3 coils and they all have spark. I checked all injectors have power signal. All the fuse under the hood is good. A mechanic suggested disconnect the CAT and see if it's stuck. I drop the whole down pipe and it's still no good. I also took out the airbox and clean the throttle body. When I cranking it, there's fire ball blowing from the rear exhaust manifold AND THE THROTTLE BODY. Alot of unburnt gas smell and some white smoke coming from the rear.

It's clear that the engine got gas and spark. There's 2 thing GM SI mentioned but I didn't check yet, 7x crank sensor and ignition control module. I'll look into those two thing later. The manual also mentioned something about the 24x crank sensor. Will this related?

I haven't do any mechanical check up yet. The engine bay is very tight to even open up the front valve cover. I doesn't really look like it's mechanical problem. I wanna do all the engine control test first.

Any other area I should check for? Any ideas? Please help since my wife was very worry about this. Thanx a million.

westerndragon
01-08-2010, 10:32 AM
it seems like a breathing problem for the engine you said it chokes at any attempt for higher rpm your not burning all your gas and the engine is choking on it when you dump

if your getting a full spark then its probably not the ignition coil

sorry i cant be more help but hold out for one of the 3400 sfi gods to decend from the arcade section lol

westerndragon
01-08-2010, 10:34 AM
it seems like a breathing problem for the engine you said it chokes at any attempt for higher rpm your not burning all your gas and the engine is choking on it when you dump

if your getting a full spark then its probably not the ignition coil

sorry i cant be more help but hold out for one of the 3400 sfi gods to decend from the arcade section lol

Darkness
01-08-2010, 11:19 AM
The problem is the car won't even start up now. So I can't do any kinda diagnose about the limited driving condition problem. I need to start it up first.

350rs
01-08-2010, 03:19 PM
check fuel pressure, sounds to me like your pump just went south

Darkness
01-08-2010, 03:26 PM
I've 42psi fuel pressure at the fuel rail. Also, I smell gas when I cranking it.

MIgrandamguy
01-08-2010, 03:50 PM
if you can find the tools, try to do a compression test on the cylinders. There's a tool one of the mechanics has at the shop i work at that he uses by taking a plug out on a cylinder and then screws this pressure tester in.

could also be timing issues, but I don't know how to/if it's easy to get to the timing chain on a 60 degree V6 motor. do some poking around www.60degreev6.com. will probably be your best bet

stonemason90
01-11-2010, 07:33 PM
It's a 3.4L from a 98 Transport Montana, any help will be appreciate. Thanx in advance. If this is not suitable in General section, Admin please move this thread.

Here's the story:
Last week my wife's van suddenly acted up at one nite. It can't rev over 3000rpm. It doesn't matter at any speed or gear, it just quit at 3k rpm. When it reach 3k rpm, it's choking and act like fuel is cutting off.

Next morning, try to start the engine and do some diagnoses. It cranked but not start. IT doesn't have any kinda SES light or code. I followed GM SI manual to diagnose the problem and here's what happened:

The MAP sensor read 104 kPa. Then I unplug the MAF sensor and it won't start. I replaced the MAP sensor, same thing. I've fuel pressure at the fuel rail with 42psi. I checked all 3 coils and they all have spark. I checked all injectors have power signal. All the fuse under the hood is good. A mechanic suggested disconnect the CAT and see if it's stuck. I drop the whole down pipe and it's still no good. I also took out the airbox and clean the throttle body. When I cranking it, there's fire ball blowing from the rear exhaust manifold AND THE THROTTLE BODY. Alot of unburnt gas smell and some white smoke coming from the rear.

It's clear that the engine got gas and spark. There's 2 thing GM SI mentioned but I didn't check yet, 7x crank sensor and ignition control module. I'll look into those two thing later. The manual also mentioned something about the 24x crank sensor. Will this related?

I haven't do any mechanical check up yet. The engine bay is very tight to even open up the front valve cover. I doesn't really look like it's mechanical problem. I wanna do all the engine control test first.

Any other area I should check for? Any ideas? Please help since my wife was very worry about this. Thanx a million.

try taking off the valve cover and having someone crank it it sounds like exactly what happened with my grand prix.... which has a twisted camshaft. if all the lifters are moving then its not broken but it doesnt rule out twisted so like he said do a compression check. what makes me think this might be the problem is the fire coming out of both the intake and the exhaust. i had a huge fireball come out of my intake and it almost sounded like i popped a cylinder it was so loud....

Darkness
01-11-2010, 10:15 PM
I did a compression test on cylinder #5 (front bank close to TB) with my mechanic friend. He said the reading looks ok. We haven't check the other cylinder yet. Since #5 is the last cylinder and it test ok, so we assume the cam is not broken.

I think I'll test the other 5 cylinder.

gagt Mechanic
01-11-2010, 11:28 PM
your 3000 rpm issue def sounds like a clogged cat.
you said that you had spark at the coils but what about at the plugs. if you have good spark good fuel and good compression, you have an ignition issue. (your spark plugs are fireing at the wrong time) this could be the ignition mod or the pick up on your cam or a bad cam/crank sensor. another posiblity is your coolant temp sensor. if it went bad and is reading like -80 it will dump gas into your eng and flood it, or the oposite and reading high, but if your temp guage dosent move with koeo it would be reading low.