Hesitation under load

[Yano]

Any advise as where to look to solve a hesitation problem with my CSI. Problem takes places only when the engine (B34 euro model) is under heavy load in second gear. The problem only happens between 3500-4000 RPM. Do not have this issue at any other RPM range or in any other gear. Any help is appreciated.

Thanks,
Glenn

 

[sfdon]

Did you install an o2 sensor or take it to a dyno?

 

[MMercury]

Any advise as where to look to solve a hesitation problem with my CSI. Problem takes places only when the engine (B34 euro model) is under heavy load in second gear. The problem only happens between 3500-4000 RPM. Do not have this issue at any other RPM range or in any other gear. Any help is appreciated.

Thanks,
Glenn

Your mention of "B34" and "csi" can be interpreted to mean many things to different people. For example, you could be referring to a larger displacement replacement block using original E9 fuel and ignition OR you could be referring to a newer engine with the newer fuel delivery and ignition systems. On newer systems, you might consider checking/cleaning the mass airflow sensor or other engine management systems. See e.g., http://forums.bimmerforums.com/forum/showthread.php?1605377-Noticable-Hesitation-in-Second-Gear

Without substantially more facts, the following thoughts are but random musings.

Second gear only hesitation on an otherwise original E9 is a head scratcher. If we assume you have a manual transmission, my first inclination is to consider what is different when you are in second gear, as opposed to the other forward gears.* Some cars are occasionally bedeviled with misfiring or stalling during turns or abrupt stops - because their distributors - or other wiring - are in close proximity to firewalls or fenders and the wiring can inadvertently chafe and short against firewalls or other body parts when the car is moving. It would be a long shot, but perhaps some part of your wiring loom is being affected when you shift into second. Is it also possible that the hesitation, as you describe it, occurs in other gears too, but seems only more pronounced in second gear?

"Generally," hesitation under load suggests a lean fuel condition. This could have any number of causes on even the most primitive of internal combustion engines, including, but not limited to: low fuel pressure, a clogged fuel filter, improper ignition timing, defective ignition coil, condenser, ignition wires, cap, rotor and excessive spark plug gap. It is even possible to have poor engine operation due to the almost unthinkable: restricted air intake or exhaust. (Think nests and bent/kinked exhaust plumbing.)

On a djet equipped csi one might pay particular attention to the fuel pressure and not overlook the injector trigger contacts (at bottom of djet distributor) and possibly even a worn or maladjusted throttle valve switch. For any of the electrical parts, e.g., senders and switches, the part itself may be fine, but a poor electrical contact due to brittle wiring or corrosion can make any part appear bad. It is unlikely, but ECU's and pressure sending units can also suffer from poor connections and are not impervious from breakdown.

A good manual with a troubleshooting guide can occasionally answer the questions you didn't think to ask. :wink:

http://www.e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/13.html#refertoc

http://www.e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/12.html#refertoc

http://www.e9coupe.com/tech/autobooks/chapter3/autobooks_manual_053.htm

*On a few non-BMW models, some emission controls of the era could affect (retard) ignition timing only in certain (top) gears. it is doubtful you are dealing with any such device or devices.