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cold start misfire


rockfangd

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well good news. I drove the car for the first time since I did the regulator on thursday. no misfire at all and the acceleration is more consistent. I feel I have to give less acceleration to get more power.

I have driven 48 miles and started the car 4 times today. no problems at all. before thursday it had been doing it pretty consistently daily

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One item no one mentioned is plug wires. If you have condensation on them under the beauty cover, one or more could be shorting to the intake manifold until a little warmth dries things out.

I changed my FPR myself several years ago. Piece of cake. Mine is held in with a snap ring. As KHE says, watch out for the little O-ring because it's easy to lose and hard to replace. If you like, I'll look up the FPR replacement in my FSM and post it.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Can you be more specific? too much or not enough.

I know my fuel economy has been terrible lately

I'm not sure if it would result in higher fuel pressure or more fuel usage.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Fuel pressure within limits won't change your mileage. If it's high enough to damage your fuel injectors that would likely cause a no-start condition. Also, FPR's don't stick.

The FPR is an analog device, with manifold vacuum on one side and fuel pressure on the other side of a diaphragm, with a spring on the diaphragm. The idea is that the diaphragm responds to manifold vacuum to operate a valve that keeps the difference between the fuel rail pressure and the manifold approximately constant. This means that the fuel injectors are easier to operate by the PCM because the amount of gas passed by a fuel injector is determined only by the pulse width (time that they are open) and the manifold vacuum doesn't have to come into the computer and modulate the pulse width too.

The problem is that the diaphragm is neoprene and wears out, eventually leaking. This will allow gas to go into the vacuum line and then to the intake manifold. The first symptom usually seen is hard starting when hot due to too much gas for good starting of a hot engine, so you have to turn it over a few times to get the excess gas out of the intake. You can usually smell gas in the exhaust just after starting, and sometimes you can smell it under the hood of a hot engine if there is some way for manifold air to get into the under-hood area, such as a loose airbox.

Hard starting when cold is not a common problem, but a really bad FPR can cause hard starting at any engine temperature.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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well I think I have nailed it. The FPR definately made a difference and I am hoping for some kind of mileage increase. It was total a 5 minute job. the longest part of the job was removing and installing the beauty cover.

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With the vacuum line disconnected, the FPR will "think" that the manifold vacuum is zero, putting the maximum regulated pressure on the fuel injectors all the time. The vacuum leak might not be audible if it's under the beauty cover. This will result in a richer-than-intended mixture at high vacuum, particularly at idle. The vacuum leak might help compensate for the rich mixture but only at idle. I'm surprised that your PCM didn't get mad and throw a code. In any case, the problem is now understood and solved. Congratulations!

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Exactly what I thought. I was shocked no codes. That is why I thought it was starting rich after it sat for a little while. So basically every startup it was getting too much fuel. another thing I had noticed before was speed wasnt consistent with steady throttle (basically cruising speed) now steady throttle picks up speed and fuel economy appears to be showing improvement

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The DFI that nearly all production cars use descended from a Bosch analog system and still has some analog parts, like the FPR, and some bang-bang parts, like the fuel injectors. I'm hoping that we will see a fuel rail pressure sensor and a PWM-operated FPR with no diaphragm someday soon, and perhaps PWM-operated fuel injectors that can output fuel in a waveform to match the intake velocity of each cylinder, not just turn it off and on. This would seem to be more of a benefit with DI than with port fuel injection.

But, that's just me. If it ain't broke, don't fix it, I suppose.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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  • 2 weeks later...

Ok well to update this. problem is still ocurring. I guess I will have to pull the rail in the spring and hope to find a leaky injector. I am bummed but nothing I can do.

GM FAN FOREVER

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How about the O2 sensors? I know that they are not active on cold start-up, but I think that the PCM uses the data for long-term fuel trim at all times (including cold start-up), and the long-term fuel trim is set based on feedback from the O2 sensors. That could explain poor fuel economy as well. I am not sure about this, but it be surprising to me if the long-term fuel trim data was not used also when there is no O2 sensor feedback, since whatever it compensates for (e.g., dirty injectors) needs to be compensated for also before the O2 sensors are warmed up.

Another thought is to connect a scan tool and see if you can get any indication as to if it is a particular cylinder that misfires, or if it is randomly misfiring on all cylinders start-up. Even if there are no codes (current or history) there can still be codes that are pending, with misfire counts attached to them. I have extracted this information by using an OBD link together with ScanXL, and I did get information on misfire counts, even though I did not have any codes that showed up on the dash (the PCM apparently determined that there were not enough misfires to set any code at that time).

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I was really kind of surprised a FPR fixed it

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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  • 2 months later...

Ok to update this. I finally Downed The deville. I have the injector kit with clips and o rings. I have to replace a coolant hose and would like to find swaybar bushings. I hope it is a leaking injector. I just hope it hasnt damaged anything else.

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A bad FPR, or a vacuum hose off the FPR as in your case, won't harm the injectors. If you're running closed loop most of the time and you aren't getting codes, then the engine will be OK.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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thanks for the reply. I still would like to figure it out. No codes at all. Even if I let the car sit for a few hours it will miss on startup for a few seconds. It never misfires while driving. just on the immediate startup

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On startup, there are several things that are different. The fuel pump runs for a couple of seconds and shuts off until the oil pressure light goes off to put enough pressure out there to start the car. The engine runs open loop until the oxygen sensors heat up and come online, which can be a minute or two. Right after startup, leakage from injectors and/or the FPR, if any, will leave part or all of the intake manifold wet and some or all of the cylinders will run in a rich condition; you should be able to shut it off and then smell gas at the tailpipes if this is happening, particularly i fit isn't firing up instantly. The plugs are cold, and until the engine warms just a little bit there may be some condensation on the plugs, plug boots, plug wires, and coils.

I think that this is a comprehensive list of things that can cause a stumble or miss on a cold start-up that won't throw a code. If the fuel pressure is OK, particularly the first thing in the morning after turning on the key just once but not starting the car, that's probably OK. If the fuel pressure doesn't bleed down from that first reading, then the FPR and injectors aren't leaking. Some leakdown may occur if the FPR is letting some gas back into the return line but that isn't leakage into the intake manifold.

If you raise the hood when you start the car and listen when it's missing, you may be able to hear arcing if it's the plugs or wires finding a little condensation.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Usually there is an rpm surge to 1200 or so when the engine starts and the oil light goes out, so the fuel pump starts. I've never heard of a Northstar having an oil light on at idle on a cold start. If the oil light doesn't go out on starting the car, that is a troublesome issue in itself that I would address before I worried about a rough idle on the first cold start in the morning.

You can test that easily enough by turning the key off and on three or four times to bring the fuel rail pressure up to 45 psi before starting the car. If that does it, I would look at the fuel pressure with a pressure gauge because that points to the fuel pump, which is not an easy job.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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What if....... the oilpump is week? Maybe takes a bit longer before the fuelpump kicks in and the fuel preassure gets temporary low?

The oil pump would not have an effect on the fuel pressure. There is a circuit to not let the engine start until oil pressure builds in case the fuel pump relay fails but that would result in excessive cranking time. He's not reporting excessive cranking time.

The oil pumps in the Northstars are the gerotor type and are very durable and long lasting. I have never heard of one being worn.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I learned something. I didnt know the northstar used a geroter style pump. I have not heard on one failing. I would say that the low oil pressure on a cold startup is not possible. It actually seems like it is running richer rather than leaner

GM FAN FOREVER

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if you do have a stall condition and can make it stall, shift the car in reverse and see if it does it. If not its egr related.

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  • 2 months later...

Ok so today I finally got the chance to pull the fuel rail to see if any injectors are leaking.

All 8 were dry. I am going to service them anyway being I pulled the rail up but was hoping for a leaking injector.

Problem has no doubt gotten worse with time. If it sits overnight it will misfire in the morning and smells like gas in the exhaust.

If it sits for about 4 hours it will misfire on startup but for a shorter length of time.

I am baffled. On another note which I dont know if it could be related, It has thrown a P0101 code for the MAF twice. Both times it happened on moderate acceleration.

You feel A stumble then the light pops on. Could this be part of the problem and maybe it just has not thrown a code til now?

No other codes at all. No matter how bad it misses it will not throw any codes

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This is a classic case of a leaking FPR (fuel pressure regulator). You can check it by removing the beauty cover, pulling the vacuum hose off it and sniffing for gas. It's an easy DIY replacement. You can get a genuine AC/Delco FPR for your 1997 Seville motor for $44 from Rock Auto.

As far as the MAF code P0101 is concerned, this is a serious red flag and should be addressed, but it is not likely a starting problem. The 1997 FSM, page 6-302, has this notice in the preliminary diagnostic aids:

Important: An improperly installed air cleaner or a distorted /missing Intake Air Duct may cause this DTC to set. Ensure air cleaner assembly / IA duct is installed correctly and that there are no kinks, folds or damage to the IA Duct or possible debris in the air cleaner assembly or the MAF sensor inlet screen that may distort the air flow.

The checklist is pretty short. The main items are to check for vacuum leaks, "especially in the following areas:"

  • MAF Sensor seal.
  • Throttle body spacer.
  • Intake manifold.
  • EGR valve, plate and tubes.
  • PCV system.
  • Brake booster and hoses.

It also says to check for a stuck or incorrect PCV valve, and a loose or missing oil dipstick or oil filler cap.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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This is on my 96 Deville but it should be the same. I did do the regulator. Genuine Delco replacement. unfortunately did not help. Did improve acceleration but did not resolve the misfire.

This thread is a continuation thread because it has not been resolved

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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