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Runs rough for about 20 seconds on cold start

Tiny
TOPHER3867
  • MEMBER
  • 2001 PONTIAC GRAND AM
  • 3.4L
  • V6
  • FWD
  • AUTOMATIC
  • 220,000 MILES
After sitting for a few hours it will run rough for about 20 seconds then straightens up and runs fine. Getting worse and now throwing code multiple cylinder misfire. Within a week I have cleaned MASS airflow, replaced MAP, replaced fuel pressure regulator, replaced fuel filter, cleaned throttle body, and was time for new air filter. Did plugs and wires and cylinder 1 coil pack 11 months ago. About five months ago had to replace everything with the belt drive system (harmonic balancer, water pump, altenator, power steering pump and pulley, compressor pulley bearing and clutch, tensioner, and idler pulley's). This problem started about a month ago and has haunted me since.
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Saturday, October 24th, 2015 AT 10:17 PM

8 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check fuel pressure with a gauge auto parts rent it also scan for codes. 52 - 59 psi
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Monday, October 26th, 2015 AT 8:18 AM
Tiny
TOPHER3867
  • MEMBER
  • 8 POSTS
Checked pressure. Key in ON pos, It's 48psi. When I turn key off it will slowly climb to 52psi, over about 2 minutes. Then over the course of an hour and 15 min it dropped to 45psi. When it's idling it's at 45psi.
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Monday, October 26th, 2015 AT 9:53 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check fuel pressure regulator pressure is to low when running. Check for a restriction in fuel filter and or line.
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Monday, October 26th, 2015 AT 12:08 PM
Tiny
TOPHER3867
  • MEMBER
  • 8 POSTS
Regulator and filter are brand new.
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Monday, October 26th, 2015 AT 12:13 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
It's either clogged in tank or pump is bad and working slow
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Monday, October 26th, 2015 AT 12:17 PM
Tiny
TOPHER3867
  • MEMBER
  • 8 POSTS
I think that the sock is clogged. It's the original pump with 220,000 miles. And as bad as the filter was I can only assume the sock is worse. If it's as bad as all signs point to, then it would be a no brainer to do pump as well. I will keep you posted. Thx for the clarity and help.
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Monday, October 26th, 2015 AT 12:37 PM
Tiny
TOPHER3867
  • MEMBER
  • 8 POSTS
It's coolant leaking into the cylinders. Still no coolant in oil either. There is an easy and free way to diagnose. Step 1, immediately after turning off your completely warmed up engine, (200°F), completely unscrew coolant cap, (*VERY SLOWLY AND EXTREMELY CAREFULLY BECAUSE THE COOLANT IS EXTREMELY HOT AND WILL BE UNDER A LOT OF PRESSURE AND WILL SERIOUSLY BURN YOU IF YOU DON'T USE CAUTION*), but leave on to keep foreign debris out. Step 2, let sit for 4 hours or longer, even overnight, with cap unscrewed ( basically want to reproduce the situation when it idles rough, but the coolant pressure is the variable). STEP 3, after sitting for prolonged period, start car. If it no longer idles rough after start up, you are leaking coolant into cylinders.
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Friday, October 30th, 2015 AT 9:34 PM
Tiny
TOPHER3867
  • MEMBER
  • 8 POSTS
UPDATE: After doing the top end gaskets, the cause for the problem was specifically the lower intake manifold gasket leaking around a couple coolant ports. Found out that it's a common issue with GM 3.4l's because of the gasket material ( plastic ) and DEX cool. Felpro perma dry intake gaskets will fix that issue, or the top end kit that contains them is HST-9071PT1.
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Saturday, November 21st, 2015 AT 10:55 PM

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