Bad engine stumbling problem - Honda Prelude Forum

devtec · 05-20-2008, 10:10 AM

Hey all,

Back in October I swapped a JDM S Spec motor into my '97 SH (same as Type S motor, but with the LSD and no ATTS). Since bringing the car back from the shop, it suffered from bad engine stumbling, where at low RPMs from about 1200-3200 RPMs while accelerating lightly or even just cruising the engine would just completely cut out and then come back to life within a second, resulting in a bad jolt. At the time the shop recommended trying a new distributor, which I did, and the problem was temporarily solved.

However, in the last month or so the problem has returned and is getting worse. The stumbling/misfiring/hesitation is now more frequent, happening every minute or so. Low end feels terrible and engine accelerates roughly up to 4000RPM, almost in a surging manner. Also, when reapplying the gas after upshifting there is always a delay of several seconds (press gas, nothing happens), then the engine will finally rev up resulting once more in a bad jolt for that shift.

I am also getting anywhere from 15 to 18 mpg city, shifting at or below 3000RPM everytime. Must be running super rich.

Some other basics: compression tested at least 220psi across the board before going in, running the JDM ECU (will try putting in my SH ECU), conversion of JDM motor was to OBDII, cap/rotor new from swap, both o2 sensors new from swap, iridium plugs and MSD wires have about 20k on them, distributor a few months old as i said.

Replaced the PCV valve, cleaned out the EGR valve, used fuel injector cleaner (BG 44K)--no fix. Also ordered a new set of NGK oem platinum plugs/NGK wires/cap/rotor to start again with those basics, but skeptical these will do anything.

Have read all the threads on the notorious hesitation problem. Mine seems slightly different, and to my knowledge this problem has never been solved anyway.

If you guys have any insights, I'd greatly appreciate it.

Artifex · 05-20-2008, 03:14 PM

Check all the main sensors. Use a voltmeter to determine if things are ok. Start with TPS and MAP sensors.

Make sure you don't run the JDM internal coil dizzy; convert it to an external coil.

Are you running the right impedance injectors?

devtec · 05-20-2008, 03:26 PM

thanks artifex, i will check the TPS and MAP sensors... I suppose the Helms will explain how to do this.

also, yes, it's all converted to running the external coil with the USDM dizzy.

I'm running the stock SH injectors, shop told me engine wouldn't start when they tried the JDM Type S injectors. I've thought about getting these stock SH injectors blueprinted since they do have 118k miles on them... but still, I am skeptical that it's the injectors.

devtec · 05-20-2008, 05:23 PM

Found the following on the internets. Sounds like a fit, but we'll see:

"Old or worn out TPS sensors cause poor gas mileage, hesitation, stumbling, poor emissions and other performance related problems. TPS sensors have a limited life span and over time build up resistance which in turn give intermittent false signals to the ECU. If you have over 100k miles and your engine is experiencing the above symptoms your TPS sensor could be the culprit. "