Startup idle acting up after new Fuel Pump Drive Module install

[Rick Shellenbarger]

I changed my Fuel Pump Drive Module this weekend because Ive been trying to narrow down a shudder my engine exhibits from time to time. The FPDM was completely corroded from salt and almost crumbled when I took it out. After the new FPDM install I reset KAM and performed the Idle learn steps... Now here's the issue: Since the FPDM change, after I start the truck, the idle drops almost to the point of stalling, then kicks back in and idles fine... Anyway, didn't do this before and the FPDM is working; any ideas?



MAF is clean, coils are new, plugs are new motorcraft OEM, 02's are new, Cats are new, fuel pressure sensor is new, Fuel pump is working, PCM updated to latest ford software (2 months ago), no vacuum leaks found using the propane method... The occasional shudder is still present in addition to the new startup idle problem.



Im starting to think the shudder is bad motor mounts, today I was leaning on the back of the truck while it was idling and I could feel the shudder shaking the back of the truck.



Datalogging shows that fuel pressure is good (45-55psi at the fuel rail at idle) and doesn't detect any misfires.



I'm pretty much at a loss of what to look for as far as the startup idle/rpm issue, I'm pretty sure there's no need to bleed the fuel lines on the gen 2 V8's as it's all done through the EVAP. Any thoughts? Similar problems and solutions?



Thanks

 

[scott degroot]

The fuel lines do not require bleeding and they would never bleed through the EVAP system if they did. The evap system is simply for fuel vapor management between the fuel tank and the engine.



Why all the new parts?

 

[Rick Shellenbarger]

I've been having some idling issues but no DTC's. idle creep, intermittent engine shaking, wideband readings bounce back and forth between 13 and 16 instead of hovering around 14.7 when the Shakes happen. Noticed that engine power doesn't always seem consistent, and that on cold starts the engine isn't very smooth for about 30 seconds.



So I did plugs and coils first, then I just started replacing things that probably should have failed 30k ago. I figured even if they weren't bad yet, they must be close. The FPDM was different though, that thing was just a pile of corroded aluminum dust, surprised it hadn't thrown a code! The evap purge valve was whistling, could hear air leaking from it... Check lines, they were good so I just replaced the part... $36. Anyway, what's got me looking at the evap system is the vapor lock symptom I get from time to time... Start the car and the RPMs drop to a near stall, then kick back up to normal. Also noticed a high fuel rail pressure at idle (60psi). All these things point to a problem with the fuel vapors being trapped in the system I thought? Anyway, wanted the check my charcoal canister but I haven't gotten to that yet. Anyway, not DTCs except for the occasional fan clutch, which I'll get to next I guess. Sucks to have to replace the entire working clutch over a bad sensor... .

 

[scott degroot]

Forget the evap system, it is a completely different entity than the liquid fuel supply system is and has nothing to do with how the liquid fuel supply system works. Trust me you are not experiencing vapor lock.



Being that you can data log what are you long term and short term fuel trims when you start the vehicle after sitting all night when it enters closed loop. What are they when it reaches operating temperature? Also what is your BARO hz reading? How many miles on the vehicle? Why did you put cats on it? What cats did you replace the OE ones with? You plumbed in a wideband O2, where did you locate it? It isn't tied in to any of the factory O2 wiring hopefully.

 

[Rick Shellenbarger]

I'll data log those things Tuesday and post the results. The wideband is wired independently to the battery and body ground. It's located a few inches away from the factory narrowband. I replaced the cats with high flows simply for more flow, figuring 130k on the oem ones might be part of the problem too. however the symptoms I'm experiencing came before the new cars.



It's nothing major, just annoying. A friend suggested that my fuel pump may be weak, and that's a possibility but this has been going on for months (rough startup idle), ...the truck trying to stall sometimes after starting is new and very intermittent.



When I bought the truck (eBay) it had an obvious miss. I found that two coil packs were bad. Not knowing how long the previous owner drove it that way I had to assume the cats were affected in a negative way. I replaced all the coils and changed the plugs. The miss was gone but the intermittent engine stumble can still be felt from time to time. Thing is, it's not consistent at all.

 

[Rick Shellenbarger]

ran the data log, long fuel trims 1 and 2 started at 1.07 each and stayed pretty much the same, rising slightly at 6 mins of running with a peak of 1.12



The short term fuel trims started at .97 and kinda bounced between there and 1.03 for 2 minutes, then they dipped slightly ranging from .95 to .82. both banks 1 and 2 on the long and short term fuel trims stayed equal to another within .01 the whole time.



The baro reading was 28.63 HG, or 97 kpa... Not sure what that means, but it didn't vary at all.



Im noticing some idle surging at deceleration, i'll see the rpms jump up about 200-300 and then settle back down. I'm also seeing the rpms dip to a near stall when going from park to drive/rev, and often when I start the truck the rpms immediately dip to a near stall and then climb back up to about the normal warmup range (900 rpm area), then they will climb to about 1200, then settle back down to around 750 once its warmed up.



The other thing worth mentioning is the throttle in drive when first accelerating. If the truck is warmed up and im completely stopped, if I just tap the gas pedal and let it go the rpms go up to around 1200 and just stay there, pulling the truck along until I hit the brakes to make the rpms go back down... All connected you think?

 

[scott degroot]

As far as the fuel trims go Ford displays that information in + or - numbers that range from 0-50. The format you are reading is more like what we see with foreign makes where 1 is even and 1.xx would be adding fuel and .xx would be removing fuel. The long terms seem a touch high but I don't think I would worry about that right now. The baro reading I was looking was teh khz reading. It is a value that is calculated by the pcm and is invaluable when looking a the health of the maf sensors.



Can you data log the fuel trims at a steady cruise of about 55 mph?

 

[Rick Shellenbarger]

Maybe I can change the reading format. I'm using my SCT x3 with data logging software. Don't know my h about it. I'll do another data log cruising tonight.



I'm going to take it to ford this Friday to see if they can figure it out. I think I have a couple different problems making it harder to diagnose the symptoms.