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It runs bad Only when hot. I've done a lot of work and

Customer Question
It runs bad Only...

It runs bad Only when hot

Mechanic's Assistant: Have you checked the coolant? Have you noticed any leaking?

Yes I've done a lot of work and cannot figure out the problem. I changed distributor, set timing, changed coolant, coolant sensor, spark plugs

Mechanic's Assistant: What is the model/year of your Honda?

2000 Honda Civic SI

Mechanic's Assistant: Are you fixing your Civic Si yourself? What have you tried so far?

E85 tuned and turbocharged

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

It runs perfect when cold

Submitted: 1 year ago.Category: Honda
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Answered in 16 minutes by:
7/30/2017
Mechanic for Honda: Dan, Technician replied 1 year ago
Dan
Dan, Technician
Category: Honda
Satisfied Customers: 26,014
Experience: Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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Mechanic for Honda: Dan, Technician replied 1 year ago

Is it setting any codes?

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Customer reply replied 1 year ago
No check engine light and it just came out of the shop last week with no codes
Mechanic for Honda: Dan, Technician replied 1 year ago

Have you checked for vacuum leaks and fuel pressure?

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Customer reply replied 1 year ago
O have a fuel pressure guage right at the fuel filter. When I installed the fuel pump a couple months back it was set at a solid 47-50 psi on a cold start. Now it reads about 40-45 psi on cold start. I haven't checked fuel pressure while it's warmed up or under while reving the engine. I did a quick glance for vacuum leaks but I don't know all the places I should check
Mechanic for Honda: Dan, Technician replied 1 year ago

I'd start by monitoring fuel pressure on a cold start and see if it drops when engine starts running bad, if so that would indicate a problem with fuel pump or fuel pressure regulator. If good them install a vacuum gauge and monitor vacuum, if vacuum drops when engine starts running rough you would want to check for a vacuum leak which would probably be the intake manifold gasket. IF all is good then next thing I'd suspect is a oxygen sensor, you can unplug oxygen sensor electrical connector to see if it runs better, if so replace oxygen sensor. Let me know how it goes or if you have more questions, thanks.

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Customer reply replied 1 year ago
I just checked fuel pressure, from a cold start it was about 43 psi. It sat and idled nicely until it got just over halfway to operating temp then boom, like someone flipped a switch it went from idling at(###) ###-####revs to 400-700 revs. Motor starts shaking and if I give it a little bit of gas it will drop to 100 revs. If I rev it past 2500 revs it will drop to zero revs and die. Fuel pressure stayed the same. Another thing I noticed (this might be completely normal) my blow off valve opens every single time I let off the gas. Even if I rev to 1500 the valve will still open..
Customer reply replied 1 year ago
I can hear air coming out of the blow off valve while at idle too (again this might be nothing)
Mechanic for Honda: Dan, Technician replied 1 year ago

As long as the blow off valve isn't leaking at idle it should be fine. Next thing I'd do is unplug the oxygen sensors to see if that helps, if not monitor vacuum. Let me know, thanks.

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Customer reply replied 1 year ago
It does sound like it's leaking at idle
Mechanic for Honda: Dan, Technician replied 1 year ago

If it is leaking while it runs fine then that still shouldn't be the problem. If it starts running rough right when it starts to leak then I'd suspect that as the problem. Let me know, thanks.

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Customer reply replied 1 year ago
started my Honda just now on a hot engine, fired up then revs started bouncing from 0-1000 revs then died. I unplugged the o2 sensor and it started right up! I couldn't believe it! Idled nicely with a few hiccups here and there but probably because the sensor was disconnected. I did however notice that the connections didn't look good.. I'll send a pic. The connector on the o2 sensor itself looked nice but the connector Thats attached to the car is questionable. It's a six pin connector and one of the slots look a bit corroded
Mechanic for Honda: Dan, Technician replied 1 year ago

Good to hear, it sounds like you probably have a bad oxygen sensor. Send me a picture of connector, thanks.

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Customer reply replied 1 year ago
It won't let me send a pic for some reason. the connector that's connected to the car looks to be burned on the outside. I am not sure where I can buy another wiring harness for this. It's an aftermarket o2 sensor. AEM wideband. I cleaned the connections with electrical cleaner and reconnected the sensor and it started alright and it would rev alright.
Mechanic for Honda: Dan, Technician replied 1 year ago

The connector looks pretty rough but pins look ok so it should be alright, it may have just been a poor connection. Let me know how it goes, thanks.

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Customer reply replied 1 year ago
I connected it fully and it still did the same thing. I just ordered a new o2 sensor.
Mechanic for Honda: Dan, Technician replied 1 year ago

I think that will take care of problem, let me know how it turns out. .Thanks.

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Customer reply replied 1 year ago
O2 sensor was not the problem with my Honda
Mechanic for Honda: Dan, Technician replied 1 year ago

Ever get problem figured out? If not I'd move onto the vacuum test.

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Customer reply replied 1 year ago
The sensor didn't help. I'm picking up a vacuum guage today and will be testing it tonight. will update you when I complete.
Mechanic for Honda: Dan, Technician replied 1 year ago

Sounds good, thanks.

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Customer reply replied 1 year ago
Lol I totally forgot my boost guage has boost and vacuum on it. My car definitely holds vacuum.
Customer reply replied 1 year ago
It idles at 20 in.Hg
Mechanic for Honda: Dan, Technician replied 1 year ago

I'm going to open question back up to see if someone else has some ideas, thanks.

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Customer reply replied 1 year ago
Alright, any new ideas would be much appreciated. Just for reference, I've replaced spark plugs, spark plug wires, coolant temp sensor, o2 sensor, distributor, ignition timing, idle air control valve, fuel pump, fuel filter, checked fuses, checked for exhaust leak, checked for vacuum leak. I don't know what else to check...
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