94 Merc Xri Efi very rough smoky idle

[Harrym]

Hey all. Been lurking and using You people’s advice for a while but have an issue I’m not comprehending. 200hp 2.5 serial OG104002. No oil pump it’s mixed in tank 50:1. Penzoil synthetic blend. Compression is 114 to 122. The motor runs fantastic at higher rpm up to 5600 and when I throttle Down to a no wake when engine warm it seems fine. But when it’s cold it’s real rough at low idle and when I give it throttle it hesitates. Then it will just up and go. Sounds like 4 cylinders instead of 6 when it’s bad. And smoky when it does this like too rich...or is that too lean? Anyway. I’ve had the motor 5 years now. 2 years ago I replaced the stator. My problem started last year. Since then, new plugs, ohm tested plug wires and coils according to my manual. New bleeder filter, tested check valves on bleeders, new thermostats, new low pressure fuel pump diaphragms, cleaned a screen after high pressure fuel pump. Not sure where to go from here but wondering what you all think? I’m pretty capable of doing most work myself with the limits of a dva meter and complete overhaul tools. Is there a choke on these things or is it controlled by the ecm? I am eventually going to send the injectors to Bucato for service but I’m doubting that’s an issue since it runs great at high Rpm. Bad Reed valves? Wouldn’t they be affecting the high end also? Timing? Tps? Pull apart vst and clean? Just not sure what to do at this point. And just today tested spark on all plugs at idle by pulling and grounding one at a time. Much in need of advise, thanks.

[JOE54]

has no choke ecm controlled ,test ALL sensors,start with air temp, idle timming, TPS setting, make sure MAP is good and working, spark arm moves full travel, to clean it up at low speed you can retard timming and set tps closer to 200 than 300, another reason I don't like premix in efi engines hope this helps ya HARRY

[Harrym]

Thanks for the help Joe. Going to research how to test those sensors. Hopefully have time tomorrow to start testing that stuff. In the meantime I’m ordering gaskets for the intake end of the engine and then it’s teardown time to get the injectors cleaned and reeds inspected/replaced. I noticed today I had a decent amount of water coming out of the thermostat hoses when cold so I’m going to replace those too. One must be stuck open partially.

[kls2020]

Manifold air temp sensor locater on upper left side of intake manifold . Helps calculate fuel mixture from idle to full throttle .
disconnected or open circuit results in +10% fuel mixture .

Engine temp sensor located in port side head between #2 and #4 sparkplugs enriches fuel mixture only until engine temp up to 90 deg F.
Open circuited or disconnected sensor results in +40% fuel mixture but no effect on full throttle mixture . Sensor making poor contact with head surface can result in rich condition .

TPI disconnected or open circuit = +40% fuel mixture at idle but no effect at WOT .

I ran tests on both of my temperature sensors just to get baseline readings and plotted graphs for each . I took a piece of half inch thick aluminum and drilled a hole in the side 3/16 " and the drill bit length deep to accept a meat thermometer probe. I tested the sensors beginning with ice water per the book and kept increasing the water temp 10 deg at a time up to 80 deg and recording the sensor output resistance at each step . then I started heating the drilled aluminum with a 60 watt shop light while watching the meat thermometer and recording these readings . I got up over 120 deg using the light bulb for heat . There is a small tip that protrudes on the manifold air sensor so I drilled another hole in the plate for this tip to fit into for better surface area contact .
It worked out pretty well for not costing anything .
With the TPI setting adjustment it helps to have the mercury test cable and has been stated already less volts = leaner idle

[Harrym]

[Harrym]

Tested the AIT sensor this evening. Seemed ok. Tested in ice water up to almot boiling water using a meat thermometer to determine temp. I got readings that fluctuated ,hot to cold, according to the manual but not exact. The manual states approximate readings so I think I’m good. The sensor definaly responded to temp changes.

[Haughton]

Mine was similar and I changed all the sensors including the tps with no change. Sent ecu to simmons to get the drivers checked and he found the map sensor was clogged up and replaced it, now it idles a lot better. I've read on here to remove the intake cover and check the port where the map sensor hose ties in. Small port so it doesnt take much to clog it up. Worth a shot.....

Also, not sure if your motor has idle box, don recommends removing it and placing a jumper on switch boxes. Very few times he ever recommends removing anything, but hard core about taking it off.

[kls2020]

If that barb fitting at the LH bottom of the intake is not clogged you can tell by pulling off the hose going to the map sensor put your own piece of tubing on and easily blow air through the fitting using your mouth .

[FlyinSooner]

sort of same issues here, discovered this post after starting my own thread. I'll be following.

[Harrym]

Mine was similar and I changed all the sensors including the tps with no change. Sent ecu to simmons to get the drivers checked and he found the map sensor was clogged up and replaced it, now it idles a lot better. I've read on here to remove the intake cover and check the port where the map sensor hose ties in. Small port so it doesnt take much to clog it up. Worth a shot.....

Also, not sure if your motor has idle box, don recommends removing it and placing a jumper on switch boxes. Very few times he ever recommends removing anything, but hard core about taking it off.

Is the idle box the small black box attached to Ecu with a small red light? I have that. Also checked all bleeder and other hose fittings. All seem ok. The one below the tps that comes from the ecu is free flow from what I determined. Anyhow I have a better update to follow.

[Harrym]

Sorry I haven’t updated in a while but No conclusion yet. After checking a few sensors I decided to do a check on the timing. Going by the book it seemed that was my problem. After adjusting everything like it should be I reconnected everything and fired it up. After a lot of cranking(that never happened before) it started and seemed fine for about a minute. Then it went back to the same condition it had before. I decided to dig deeper into the fuel system. I have since removed everything from the vst to the reeds. The 1st thing I noticed was some of the hoses were a lot older than they looked. They all need replaced. Recently I did replace all the fuel lines from the tank to the LP fuel pump. So that should be good. When I removed the cone filter from the vst to HpFP it was about 3/4 clogged with stuff that looked liked it would be out of a bathroom sink drain. The intake itself looked clean until I pulled the injector filters. They looked pretty dark but not clogged. Like there’s fine bits of black hose through the system. The reeds look great. They are a black synthetic against a black synthetic material. I’m sending the injectors out to be cleaned and replacing all the hoses, filters and gaskets I can. I don’t know if this will fix my problem but it definaltly can’t hurt to replace all this stuff. And except for the injector cleaning it’s not to costly. So hopefully I’ll have a good update in a week or so.

[kls2020]

Well you found stuff that was wrong with the clogged filters and bad hoses are the culprit a lot of time so maybe you got it ?

[Harrym]

An update. Completely disassembled fuel system, cleaned, replaced all fuel lines from from lower cowling to intake, new LP fuel pump valves/dighrams and new hose clamps. My injectors have been sent to BrucatoFis for service. All gaskets are ordered and should be here soon. After a 2nd inspection of my reeds still attached to the adapter plate I started to see lots of light. 2 of them had corners that were lifted and 2 of them looked fairly bowed in the middle. They are a 2 part synthetic. I’ve had this Motor 5 years and they’ve never been replaced so I ordered a new set from Tdr. Cleaned all the cages with 600 sand paper on a mirror. (On a few openings I can still see the faint depression caused by the Oem stainless reeds. As soon as I get everything I’ll start reassembly and update you on the progress. Oh yeah. I have 2 brass fittings in my intake parts tray that I’m not sure where they come from...but I’m not �� I’ll figure it out.

[JOE54]

well be waiting for report