Mechanics

VEHICLE IS HARD TO START, STALLS FREQUENTLY AND MISSES/CHUGS AT IDLE.

1998 Chevrolet Monte Carlo • 160,000 miles

I KNOW THIS IS A LOT OF INFO, but I am hoping to avoid any unnecessary communications. I will give you everything I have done so far. I am a Honda technician, 12 years, and our fuel systems are a bit different than Chevy. I am trying to help out a friend. This car is hard to start, requiring clear flood every time to get it running(pedal to the floor while starting). I checked basic stuff like feedback from the tps, got.92 V at closed throttle and about 4 volts from WOT, so pretty normal (for a Honda). Had voltage and ground at IAC valve. Removed IAC valve and checked for carbon clogging, bent/stuck pintle. Pintle moves when key is cycled on and off. Cleaned out air passage at IAC. While car is running I can pull the plug wires from 2 and 4 at the same time and it doesn't make any difference. I'm getting plenty of spark from both wires.
Removed plugs and found that both were old and very wet with fuel. Installed two "new" plugs to test it, no change. If number 6 wire is pulled the car dies. So no contribution from 2 and 4. I'm trying not to get to involved with this thing until I get some more info from someone who is more familiar with this vehicles common problems. Not sure how to go about testing the mass air flow sensor since Hondas don't have them. I checked the vacuum hoses, and the air induction boot and found no vacuum leaks. Tested vacuum at "idle" from port on intake plenum-21 inches. Pretty good again, right? Where do I go from here? I am thinking maybe a couple of injectors stuck wide open. The guy says that this problem has been getting worse and worse until now the car will barely start.
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Hondatech739
December 7, 2011.




Have done a compression test yet?I would if your not getting any power contribution from 2 and 4 cyl and spark is good I doubt two injectors have failed at the same time. So does it run like two cylinders arent running?Also have you checked for codes?How about checking the coolant temp sensor especaily since you have to go to clear flood mode to start it.

Saturntech9
Dec 7, 2011.
I couldn't do a compression test today because I didn't take the tester with me to the house. I was going to check it tomorrow.
It does run like two cylinders aren't running. Very lopey idle, BUT, when I can get it running I can get the RPM up to about 5700, and it feels smooth. I know it requires less compression to do that, so that could be the problem. I haven't checked the codes yet because I don't have a code reader. Just didn't get one because I'm getting out of the business. I figured if I could get it running, I'd take it to Autozone and get them to read it. The coolant temp sensor is something I had forgotten about. I'll give that a shot tomorrow, too, if the compression checks okay. Thanks for jogging my memory.

Hondatech739
Dec 8, 2011.
The coolant temp sensor isnt going to cause to dead holes I just mention that because of the clear flood starting. Let me know how the compression checks out.
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Saturntech9
Dec 8, 2011.
Okay, so the compression is not great on 2-90 PSI, probably just washed out from the excess fuel. The number 4 is at 150 psi. I have the temp sensor out, I just need to know the resistance readings to test it, and which terminals to check. Hondas have separate sending unit and tw sensors, this one looks like an all in one? Thanks very much.

Hondatech739
Dec 9, 2011.
Does it have the 3.1L or 3.8L engine?The low compressionsounds like a valve issue the excessive unburned fuel would be from the low compression. Try air drying the cylinders and retest the compression.I would also test the compression of all the cylinders I always check them all just to make sure there arent any suprises. Let me know.

Saturntech9
Dec 9, 2011.
To do a real compression test all cylinders must be checked because no cylinder should be less then 70 percent of the highest cylinder compression. Also no cylinder under 100 psi.

Saturntech9
Dec 9, 2011.
I found the problem. I noticed that during cranking there was a strong fuel smell. Got my buddy to crank it while I checked. Found a large amount of fuel in the THROTTLE BODY and INTAKE. Found that fuel pressure regulator had failed and was allowing fuel to go directly into the intake plenum through the vacuum tube and run into the cylinders. Replaced the regulator, changed the oil and spark plugs (both full of fuel) and now she runs like a champ. Never seen that before. Also checked compression on cylinder one after oil change, and found it at 145 psi. A little oil on the cylinder walls goes a long way. Thanks for your help.

Hondatech739
Dec 9, 2011.
Your welcome I have seen fuel pressure regulators leak fuel in thru the vacuum diapharms of the fuel pressure regulators on the gm vechiles before. Glad you got it all fixed now your buddy owes you a nice steak dinner lol.

Saturntech9
Dec 9, 2011.

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