2000 olds intrigue 3.5L misfire no code

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BLUE

2000 olds intrigue 3.5L misfire no code

Unread post by BLUE » Wed Aug 11, 2021 5:19 pm

Hi,

Ive been chasing a misfire in this car for quite some time. It doesnt give me a code for this. The misfire is almost always at low rpms, or when initially accelerating. At first start, i put into reverse it stalls. I restart it, then it drives ok, or sometimes does this misfire thing or it will accellerate slightly without me hitting the gas. I assume this is a vacuume leak. I have replaced: fuel pump, fuel filter, sparkplugs, upper intake manifold gaskets, vent canister solenoid, cleaned canister as well, cleaned fuel injectors( all are functioning) replaced all noticable vacuum connections and hoses that Im aware of. Did a fuel pressure test which shows the fpr is functioning, but the pressure is only 38 psi. I recently replaced the IAC, and notice surging issues with it after a drive, it doesnt seem to reset so I ordered another one. Ive tested these sensors and they are functioning:MAP, MAF, TPS. I have tested the resistance on the coil packs, but dont know what the specs are for them, I dont think they are the issue.
There are trans codes 0716, 0741 , p1689, p1887, but I can reset the battery and the car will operate fine for a time. Ive even replaced a bad wire in the trans harness
I really want to address this misfire, is there anywhere else I may have missed a leak?
Is the transmission causing the misfire?

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carriedi
Posts: 2445
Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon

Re: 2000 olds intrigue 3.5L misfire no code

Unread post by carriedi » Thu Aug 12, 2021 9:31 am

from the description, I would look at the trans as the problem. If clearing the codes also clears the problem until the car acts up and the codes come back.

If the car is misfiring it could show up on a scanner that has a misfire counter PID. You can have misfires that won't set a misfire code (as in P0300 or P0301-6) Driving the vehicle with a scanner on the misfire counter on, you could see if when you feel the misfire, does it show up on the misfire counter? If it isn't showing up on the misfire counter then drive with scanner looking at the transmission PIDs up and see if the misfire feeling shows up in a trans PID.

the misfire you feel could be a trans shudder. Torque converter or torque converter solenoid... Bad input sensor...

If your car is actually misfiring like a coil or spark plug or injector problem, why would clearing the codes make it stop missing for a while? Anything is possible but that's why using the misfire counter would really help you decide what direction you should look at. I have had GM engines that have felt misfires and cleaning the fuel injectors clears up the problem but those cars had misfire codes in the computer's memory. A motorvac or fuel injector cleaning gas additive can clear up the dirty injector and get rid of the misfiring problem.

Here's the thing, currently, cars really need a good scanner so you can see what the vehicle is reacting too. Driving around and being able to save the graphs to look at what acted up when the problem happens is critical to diagnosing where to go in your diagnosis direction. For example if this was a Ford, I would look at the misfire counter because many times you can feel the misfire and the misfire counter will see and record the misfire but it won't turn on the engine light or set a hard code for the misfire because the misfire percentage is not high enough to set the code. Even though you can feel it misfiring. GM, not so much. The percentage is usually low enough that it you feel a misfire it will set the code for the misfire.

Also, if there is a vacuum leak you should see it in the IAC, O2 and rmps. Look at a problem with the cold air intake like a split or crack that opens when the engine torques over. Graphing the fuelrich/lean O2 sensor. Vacuum leak should show a lean condition. Fuel pressure and/or a fuel filter could also cause a lean condition that would cause a lean misfire. that should show up while looking at the misfire counter and also looking at the O2 sensor readings.

Based on the codes, It would look like a trans problem would need to be looked at first. Well, first if the misfire counter doesn't show an actual misfire when the vehicle is acting up. Let me know what you find out.

Blue

Re: 2000 olds intrigue 3.5L misfire no code

Unread post by Blue » Fri Oct 01, 2021 1:53 pm

Thank you so much for your reply, I dont have a scanner, I usually borrow from Oreilleys. What I have noticed is if I start the car, shut it off and then start again at least 2 to 3x's, it will not stall in reverse nor will it shudder. So now if the car starts to misfire (in low rpms only), I shut it off and start it to clear it up. I also replaced the fpr, and have been replacing bad vacuum lines as I find them in attempt to get better gas milage. Along with trans codes are P1689, p0440, p0442, p0446, and p0340. I aslo suspect electrical issues as I noticed the battery/chassis ground has corrosion creeping down in the insulation. I would like to add another ground to engine/chassis.
Question: for the p0446, how much vacuum should be on the line from purge to vent solenoid?

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carriedi
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Joined: Wed Apr 10, 2013 12:42 pm
Location: Oregon

Re: 2000 olds intrigue 3.5L misfire no code

Unread post by carriedi » Mon Oct 04, 2021 3:20 am

for P0446 I would look at the canister purge and vent valves. Make sure the gas cap is good.

the computer looks at the pressure sensor in the fuel tank when it switches the purge and vent solenoids. If the vacuum and pressures don't match what the computer is looking for the codes are set.

that's why you need to use a good scanner. Testing is done by having the scanner switching the solenoids to verify operation and watching the fuel tank pressure sensor changes. Many times the purge and vent valves (solenoids) will act intermittently. That's why using a scan tool to turn the valve on and off many times to see if they get stuck and stop responding the the commands from the computer.

I would want to look at the P0340 code first, for the possible misfire. That's for the cam sensor. the computer uses the cam and the crank sensors to fire the spark plugs and the fuel injectors.

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