Brand new rebuild installation, 1998 buick 3800SC. starts and idles Perfect, but pull the throttle Quickly,(NOT under load, just sitting in park,) and it bogs ! the only things Not Changed are the MAF and O2 sensors. Ideas? anyone run into this before ? Shows No CODES. Thanks
A MAF covered with a film of dried oil from a reusable air filter, or just dirt, will cause exactly what you are describing. Take out the MAF and look to see if it looks different front to back vs back to front. There is MAF cleaner. Break the wires and of course the MAF is crap.
The oil covering insulates the wire causing it to react slowly to air flow changes.
Harbor Freight has a reasonably priced set of bits $9.97
Brand new rebuild installation, 1998 buick 3800SC. starts and idles Perfect, but pull the throttle Quickly,(NOT under load, just sitting in park,) and it bogs ! the only things Not Changed are the MAF and O2 sensors. Ideas? anyone run into this before ? Shows No CODES. Thanks
Still have the stock 2.8 pump in the tank, ( I have the correct one, but have not installed it yet), but should that make a difference" when it's just standing still" ? This engine acted the same way BEFORE I removed it from the Riviera (no Power), so I'm guessing the MAF, just didn't want to drop $100 if that's not it. In the Riviera , Before I pulled the engine, it gave a MAF code and misfire #5, Now it "Shows" No Codes. so I guess I'll just get one and hope that's it. So, it Can't be the O2 ? ( If I don't need one, I'd rather not buy one). Thanks
I used to have a GTP. I never really revved the motor in park. but I can tell you I had really bad KNOCK RETARD which made the car bog at medium throttle. The sensor is really sensitive on some cars and picks up knocks outside such as a loose exhaust clamp, loose motor mounts things you just wouldn't expect to affect the sensor. Well, I didnt answer your question but when you figure it out and you will.. Let us know!
------------------ Tim and Lynn 1987 Fastback GT in restore mode..
Fuel pressure is too low. Install a higher flow rateed unit.( corvette FP ) Yes even at idle it runs fine, in drive there is more load on the pump/engine.
Plugs/wires ENGINE, Everything is NEW, except MAF and O2. And orig fuel pump. But it won't Rev "Properly " In Nuetral" Standing Still, not even once. Fuel pressure at about 40 (gauge Connected.)
The last set of plug wires I bought had 1 wire that was no good. Luckily I metered them before I installed them. After replacing the plugs and wires (just last night) I took it for a short drive and I actually got the tires to spin. I was having a stumbling issue as well. When I get off work today I'm gonna take it for a longer drive, but I think my issue is fixed. I too didn't have any codes that read misfire or anything like that when I was having my issue.
I am going to install the new pump. But, "seems to me", If Fuel pressure was the problem, it wouldn't have been happening while it was still installed in the Riviera.
You had a fiero 2.8 fuel pump in your Rivera? Do a search for fuel pumps for the 3800sc.Tthere are many opions on which one is the best to use. I have always used the EP3** kind.( forgot the #) vette pump- direct replacement
"You had a fiero 2.8 fuel pump in your Rivera", WHERE did you get THAT ?? when the engine was still in the Riviera, it still had the Riviera fuel pump running it, but still had "No Power", so I would tend to believe that pressure may not be the problem. ( I Have a suitable high pressure pump to install) I ordered a new MAF.
if it can run Fine without the MAF, I heard it will not, why are so many saying that these symptoms are of a bad or dirty MAF ? I'm open to "OTHER" suggestions.
In earlier EFI, GM used either a 'speed density' calculation to measure the air flowing into the engine, or a MAF to measure it. Neither are perfect. On the 3800 GM uses both, thus giving the PCM better measurements of actual air flow, and giving the full sized car owner a redundant system that works pretty good even if one sensor totally fails.
If a sensor however doesn't totally fail, but instead gives bad info to the PCM, the PCM will act on that bad information and produce bad outputs.
[This message has been edited by phonedawgz (edited 03-13-2014).]
" 'speed density' calculation to measure the air flowing into the engine, or a MAF to measure it. Neither are perfect. On the 3800 GM uses BOTH," so where is this "other" sensor ? Can IT be replaced ? New MAF will be here Monday. Thanks
The stock Fiero ECM is based on speed density. Speed density calculations rely primarily on the MAP, IAT sensors and RPM of the engine. It uses the TPS to calculate acceleration enrichment, if you unplug the TPS in on a SD ECM you will have horrible throttle response but it will keep a steady speed like a champ... heck even a MAF system will be sluggish with no TPS...
The stock Fiero ECM falls back to an 'limp home' mode if the MAP is disconnected or fails... that is purely throttle position and RPM, it has no concept of load at that point and so it is programmed to run fairly rich to be safe...
GM MAF based ECMs fall back to speed density if the MAF fails and probably even the same 'limp home' mode of the Fiero ECM if very bad things have happened.
[This message has been edited by carbon (edited 03-14-2014).]
It is used to determine if the throttle is closed and the PCM should be controlling the idle speed.
It is used when you move the throttle quickly so the PCM knows to add extra fuel.
Since you are not getting a TPS code, it must be working at least some. If your TPS has a bad spot on it that spot can be read by the ECM as a quick movement of the throttle.
Not much chance however of the TPS causing this the way I look at it. If you have a scanner, turn it on, read the TPS - key on engine off - and slowly push the throttle open. If the scanner shows anything but your smooth throttle opening then suspect a bad TPS.
SD uses MAP, RPM and IAT to determine air charge, not TPS. TPS is quite useless when trying to calculate how much air is in the intake manifold compared to the MAP.
[This message has been edited by phonedawgz (edited 03-14-2014).]
