Why does it bog when cold?
Thread Starter
Member
Joined: Nov 1999
Posts: 429
Likes: 0
From: Fayetteville, Arkansas, USA
Car: 1994 Trans Am
Engine: 5.7L LT1
Transmission: 6-speed
Why does it bog when cold?
I get crappy throttle response from my IROC when I start it up cold. In neutral, pressing the gas pedal slightly causes the engine to bog, sputter and generally idle like *** . Even in drive the response is not even and the engine again sputters and bogs. What could be the reason? I know my TPS is fine. I suspect the plug gap and the coolant temp sensor are the culprits. I pulled the drivers side plugs yesterday, and they were all gapped more than .045" The factory recommended gap on my motor is .035" I gapped them properly and reinstalled them. Now starting is a whole lot better - thats only with 4 properly gapped plugs. But the cold condition I mentioned earlier still persists. What do you think could be causing this. I need a logical explanation. I'm planning to do a complete tune up soon anyway, but I have a feeling it won't fix this. Bad plug wires wouldn't have anything to do with this right? Otherwise it would run like crap all the time.
------------------
'88 IROC 305 TPI
Gutted airboxes
160 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel
Ram-air setup coming soon
Flowmaster muffler
------------------
'88 IROC 305 TPI
Gutted airboxes
160 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel
Ram-air setup coming soon
Flowmaster muffler
Moderator
Joined: Jan 2000
Posts: 19,659
Likes: 310
88,
Do the complete tune up really soon. That will likely take care of most of your problems. Remember that a complete tune up should be as follows:
BASIC TUNE UP
A basic tune-up MUST include:
* Cooling system inspection;
* Clean or replace spark plugs;
* Ignition wire testing;
* Distributor cap/rotor (if you don't have the OptiSpark);
* PCV valve cleaning or replacement;
* Air filter;
* Cleaning the IAC;
* Checking/setting TPS voltage;
* Check/adjust minimum air rate;
* Check/adjust timing;
* Code scan;
If the fuel injection system is suspected,
the proper steps in fuel injector system service are:
* Check fuel pump operating pressure and volume.
* Test pressure regulator for operation and leakage.
* Flush entire fuel rail and upper fuel injector screens to include pressure regulator.
* Clean fuel injectors.
* Decarbon engine assembly.
* Clean throttle plate and idle air control (IAC) passages.
* Check minimum air flow rate and adjust if needed.
* Relearn onboard computer.
Cleaning injectors is not a "basic" tune-up procedure.
To clean the injectors and system correctly takes about two hours if you're experienced and have all the right equipment, about four hours longer if it is your first time and/or you only have basic tools and instruments. When performing this, you should also test fuel pump output volume and pressure - these are critical to proper operation of the system. You can have the fuel system power-flushed, but most of us don't have the equipment to perform this at home. This seems to be a good procedure if done correctly.
The advantage to the old-fashioned way of cleaning injectors is that you get to actually see the injector screens and spray tips. And while you have everything disassembled, you can easily do the intake plenum modifications that the factory should have done. You can also clean up that mess under the plenum and fuel rails, and get a good look at the EGR, which should be pulled and inspected if you're already that far. Once you perform this, you'll appreciate the need for using good fuel and keeping a clean fuel filter.
USING GOOD FUEL
"Good" fuel is relative. If you have a performance engine, you're probably pushing the edge in several aspects. If you've optimized your timing, mixture, and aspiration, you probably have a relatively high combustion pressure. That's the goal in a performance engine, more pressure means more torque. This is not necessarily compression pressure, but combustion pressure.
If your PCM notices knocking, a lean condition at the O2 sensor, low MAP, or any of many other variables, it will adjust the spark timing and fuel rate to "detune" your engine so that it doesn't destroy itself. Using a higher octane rated fuel will allow you to take advantage of the maximum limits of program parameters in your PCM. You may actually notice a reduction in fuel mileage at highway cruise speeds because of a likely lower cetane rating of the fuel. GM recommends at least 91 octane in most of their performance vehicles. I try to use 94
whenever I can. I have been in some places where I can only find 92, and it is called "premium". Your car will probably run on very low octane fuel, but the performance will be degraded.
Along with octane, fuel cleanliness is important. If you live in an area where steel storage tanks are still used, you risk getting debris in your fuel. Where I'm at, USEPA and IEPA LUST regulations have forced most suppliers to change to fiberglass double-containment storage tanks. Since most of these are newer, I am not as concerned about debris. I also like seeing the
in-line filters at the pump. Your own fuel filter is important to maintain as well.
I also try to use blended fuel as often as possible. The ethanol helps reduce moisture in the fuel and tends to keep deposits to a minimum. I have used ethanol blends since 1976 and have only had one problem - the fuel bowl float in the Holley on my 1967 Firebird dissolved in the alcohol. This happened in 1976, and all synthetic materials used in fuel systems have been compatible with alcohol since the late ‘70s. Since the combustion rate of alcohol is slightly lower than gasoline, blended fuels get a higher octane from the alcohol. Therefore, fewer
additives are formulated in to achieve the same result, and these are usually the additives that cause deposits in the fuel system, on valves, and in the chambers.
I don't want to get into the battle over alcohol, gasoline, and why you supposedly lose power with alcohol. Suffice it to say that those who have a weak chemistry background don't understand the molecular conversion of the combustion process, and that power is made more by expanding gasses converted from fuel, not hot gasses and the relative BTUs created by burning a given fuel. If you doubt this, think about the reasons 3,000 HP drag engines use alcohol instead of oil hydrocarbons.
The best advice I can give is to purchase fuel at a reputable dealer who has a relatively high sales volume. You are a lot less likely to get moisture and debris in the fuel. Using premium grade fuels will increase your chances of getting fuel with fewer contaminants since it refined hotter and/or has increased octane additives. Using blended fuel will reduce the amounts of other non-fuel additives that tend to form
deposits. There is also the theory that buying fuel at a station where the storage tanks are being filled increases the chance of contaminants, since the fuel in the storage tanks is being stirred. While this may be true, I suspect that this stirring goes on for quite some time after the fuel has been delivered, and there is no way to tell how long ago the tanks were filled - it may have been just before you arrived. Another good reason for filters at the pump.
It is very important to keep your fuel cap clean and tight. Any of you with ‘94 and newer cars would know this by the "Service Engine" light being triggered by a cap that isn't sealed. Normal aspiration of the fuel tank will admit moisture and atmospheric dust to the system. This dust and moisture can damage injector nozzles.
Finally, fuel system and injector cleaners in a can may or may not be a good thing. "Cleaning" injectors in this way is not the best method. And cleaners with butyl cellusolve are not compatible with many fuel additives blended in at the refineries. Trying to clean engine parts by pouring junk in the tank is probably about as effective as Slick50 in your oil , or that Motor-Up crap I've seen advertised on late-night TV. Keep using this stuff, and you'll keep your favorite mechanic a very happy guy!
After performing this correctly, you may still have a hesitation problem at throttle tip-in. but the possible causes will be a lot less variable.
------------------
Later,
Vader
------------------
"Make Me Bad"
Adobe Acrobat Reader 4.0
Do the complete tune up really soon. That will likely take care of most of your problems. Remember that a complete tune up should be as follows:
BASIC TUNE UP
A basic tune-up MUST include:
* Cooling system inspection;
* Clean or replace spark plugs;
* Ignition wire testing;
* Distributor cap/rotor (if you don't have the OptiSpark);
* PCV valve cleaning or replacement;
* Air filter;
* Cleaning the IAC;
* Checking/setting TPS voltage;
* Check/adjust minimum air rate;
* Check/adjust timing;
* Code scan;
If the fuel injection system is suspected,
the proper steps in fuel injector system service are:
* Check fuel pump operating pressure and volume.
* Test pressure regulator for operation and leakage.
* Flush entire fuel rail and upper fuel injector screens to include pressure regulator.
* Clean fuel injectors.
* Decarbon engine assembly.
* Clean throttle plate and idle air control (IAC) passages.
* Check minimum air flow rate and adjust if needed.
* Relearn onboard computer.
Cleaning injectors is not a "basic" tune-up procedure.
To clean the injectors and system correctly takes about two hours if you're experienced and have all the right equipment, about four hours longer if it is your first time and/or you only have basic tools and instruments. When performing this, you should also test fuel pump output volume and pressure - these are critical to proper operation of the system. You can have the fuel system power-flushed, but most of us don't have the equipment to perform this at home. This seems to be a good procedure if done correctly.
The advantage to the old-fashioned way of cleaning injectors is that you get to actually see the injector screens and spray tips. And while you have everything disassembled, you can easily do the intake plenum modifications that the factory should have done. You can also clean up that mess under the plenum and fuel rails, and get a good look at the EGR, which should be pulled and inspected if you're already that far. Once you perform this, you'll appreciate the need for using good fuel and keeping a clean fuel filter.
USING GOOD FUEL
"Good" fuel is relative. If you have a performance engine, you're probably pushing the edge in several aspects. If you've optimized your timing, mixture, and aspiration, you probably have a relatively high combustion pressure. That's the goal in a performance engine, more pressure means more torque. This is not necessarily compression pressure, but combustion pressure.
If your PCM notices knocking, a lean condition at the O2 sensor, low MAP, or any of many other variables, it will adjust the spark timing and fuel rate to "detune" your engine so that it doesn't destroy itself. Using a higher octane rated fuel will allow you to take advantage of the maximum limits of program parameters in your PCM. You may actually notice a reduction in fuel mileage at highway cruise speeds because of a likely lower cetane rating of the fuel. GM recommends at least 91 octane in most of their performance vehicles. I try to use 94
whenever I can. I have been in some places where I can only find 92, and it is called "premium". Your car will probably run on very low octane fuel, but the performance will be degraded.
Along with octane, fuel cleanliness is important. If you live in an area where steel storage tanks are still used, you risk getting debris in your fuel. Where I'm at, USEPA and IEPA LUST regulations have forced most suppliers to change to fiberglass double-containment storage tanks. Since most of these are newer, I am not as concerned about debris. I also like seeing the
in-line filters at the pump. Your own fuel filter is important to maintain as well.
I also try to use blended fuel as often as possible. The ethanol helps reduce moisture in the fuel and tends to keep deposits to a minimum. I have used ethanol blends since 1976 and have only had one problem - the fuel bowl float in the Holley on my 1967 Firebird dissolved in the alcohol. This happened in 1976, and all synthetic materials used in fuel systems have been compatible with alcohol since the late ‘70s. Since the combustion rate of alcohol is slightly lower than gasoline, blended fuels get a higher octane from the alcohol. Therefore, fewer
additives are formulated in to achieve the same result, and these are usually the additives that cause deposits in the fuel system, on valves, and in the chambers.
I don't want to get into the battle over alcohol, gasoline, and why you supposedly lose power with alcohol. Suffice it to say that those who have a weak chemistry background don't understand the molecular conversion of the combustion process, and that power is made more by expanding gasses converted from fuel, not hot gasses and the relative BTUs created by burning a given fuel. If you doubt this, think about the reasons 3,000 HP drag engines use alcohol instead of oil hydrocarbons.
The best advice I can give is to purchase fuel at a reputable dealer who has a relatively high sales volume. You are a lot less likely to get moisture and debris in the fuel. Using premium grade fuels will increase your chances of getting fuel with fewer contaminants since it refined hotter and/or has increased octane additives. Using blended fuel will reduce the amounts of other non-fuel additives that tend to form
deposits. There is also the theory that buying fuel at a station where the storage tanks are being filled increases the chance of contaminants, since the fuel in the storage tanks is being stirred. While this may be true, I suspect that this stirring goes on for quite some time after the fuel has been delivered, and there is no way to tell how long ago the tanks were filled - it may have been just before you arrived. Another good reason for filters at the pump.
It is very important to keep your fuel cap clean and tight. Any of you with ‘94 and newer cars would know this by the "Service Engine" light being triggered by a cap that isn't sealed. Normal aspiration of the fuel tank will admit moisture and atmospheric dust to the system. This dust and moisture can damage injector nozzles.
Finally, fuel system and injector cleaners in a can may or may not be a good thing. "Cleaning" injectors in this way is not the best method. And cleaners with butyl cellusolve are not compatible with many fuel additives blended in at the refineries. Trying to clean engine parts by pouring junk in the tank is probably about as effective as Slick50 in your oil , or that Motor-Up crap I've seen advertised on late-night TV. Keep using this stuff, and you'll keep your favorite mechanic a very happy guy!
After performing this correctly, you may still have a hesitation problem at throttle tip-in. but the possible causes will be a lot less variable.
------------------
Later,
Vader
------------------
"Make Me Bad"
Adobe Acrobat Reader 4.0
Thread Starter
Member
Joined: Nov 1999
Posts: 429
Likes: 0
From: Fayetteville, Arkansas, USA
Car: 1994 Trans Am
Engine: 5.7L LT1
Transmission: 6-speed
I feel good man! I managed to pull out 7 of those infernal plugs on my IROC from the top with a ****ty basic toolkit. No extension or swivel joints, only a rachet set and plug wrench. Anyway, I could tell the plugs are old because there was a bit of rust on the outside, but the business end was in perfect condition, not worn out or any such thing. The only thing that I couldn't figure out was why the electrode had yellowish deposits. My Haynes manual says its high speed glazing, whatever that is. The deposits were similar to what I found on the electrodes inside the distributor cap - not cruddy deposits but a thin yellowish coating on the electrode. As I mentioned earlier, the plugs were gapped way too high. So I cleaned and gapped them properly and the hesitation and bogging disappeared to quite an extent. I don't think I need to change these plugs - they are not worn out at all.
My friends '95 V6 Camaro had the same problem at all temperatures and changing the plug wires solved the problem. It might work for me too.
As for fuel, 93 octane is the highest we get here, so that's what I use. When the green is tight I switch to the next lowest, 89 octane. I noticed slightly better throttle response with 89, but it might be my imagination. I have used 87 a few times too and lost quite a bit of power but never heard any knocking from the motor.
------------------
'88 IROC 305 TPI
Gutted airboxes
160 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel
Ram-air setup coming soon
Flowmaster muffler
My friends '95 V6 Camaro had the same problem at all temperatures and changing the plug wires solved the problem. It might work for me too.
As for fuel, 93 octane is the highest we get here, so that's what I use. When the green is tight I switch to the next lowest, 89 octane. I noticed slightly better throttle response with 89, but it might be my imagination. I have used 87 a few times too and lost quite a bit of power but never heard any knocking from the motor.
------------------
'88 IROC 305 TPI
Gutted airboxes
160 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel
Ram-air setup coming soon
Flowmaster muffler
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