LT1 running rich - not sure where to go next?

[SenselessSteve]

Hi all. It's my first thread so I better start with a "thank you" for all the information I have been able to get from the great people of Team Talk. Some really supper threads that have helped me a lot! I live in Ireland so it's tough to rub shoulders with trained mastercraft techs/engineer here.

Recently I sold my faithful 89 Pro Star (running perfectly with Ford 351) and bought a 1995 PS LT1 at auction. It was "sold as seen" and I got it for a bargain knowing that I would have to spend a bit of time with it to get it right. Really love the boat shape and the engine.. I'm not a MC engineer by any means but I'd say I'm a keen enthusiast when it comes to mechanical work.

I quickly diagnosed a problem as the engine was hydraulic locked with water in one bore (hole in one head between water and oil way) so I rebuilt the top end of the engine, replacing seals and gaskets, thermostats etc. checked all water ways and cooling system and replaced raw water impeller. Also replaced ETC sensor.

I should also say that the boat had been gas converted to run LPG so there were 8 taps in the inlet manifold that I welded as I wanted/and still want to run on petrol.

After starting the engine at the weekend, it 's running really lumpy and super rich with plumes of black smoke and unburned fuel coming out. Checked plugs and all were black and sooty really quickly. I've confirmed ETC sensor is ok with a resistance test and checked fuel pressure at rail. I had a spare GM MAP sensor so changed it also (as you may have guessed - no diagnostic support in Ireland...). Spark tested for crossfire.

Sure I'm forgetting something... Oh yeah.. Drained gas tank and filled with fresh fuel. Checked and cleaned all wiring harnesses.

And now to the question (sorry for lengthy build up)..

I'm thinking that it must be 1 of 2 things that I've not yet checked but wondered if any of you guys could help.

1 - the knock sensor? If faulty, Could the ECM be retarding timing and adding fuel to try to avoid detonation? I've tried the "brut force" method to check the knock sensor and didn't seem to get any reduction in rpm no matter how hard I hit the engine mounting (or tapped block at close range)

2 - The ECM/ECU? Is it possible that there may have been remapping for the LPG system that was in the boat before I had it? Have any of you guys converted to LPG or could any of the techs shed any light on this?

Thanks in advance for any input. All welcome..

G'luck

[1redTA]

my first thought is to check for a vacuum leak with some carb cleaner

[mikeg205]

The ECU must have been remapped for the LPG conversion - you can have it reflashed by sending it Indmar. Probably more to it. Hopefully the engine gurus will chime in soon.

[SenselessSteve]

Thanks for the replies Gents.

I tried looking for a vacuum leak (especially around my blanks that I sealed off the LPG inlets on the manifold) but the motor was hunting so much I decided I couldn't be confident of any change.

Unfortunately because it was an auction purchase I have no way to contact previous owners to confirm if the ECM was remapped so that's good news that this can be looked into Mike. Thanks! This might be a route to go down soon.

Does anyone know the resistance to send a test signal to ECM from knock sensor?

[SenselessSteve]

Also - does anyone know the GM part number for the MAP sensor ? Although I changed this (with a used sensor I had in my shed) I just want to make sure it's the correct one.

Also -can I get some sort of diagnostic using a LED and a paperclip?

[JimN]

Thanks for the replies Gents.

I tried looking for a vacuum leak (especially around my blanks that I sealed off the LPG inlets on the manifold) but the motor was hunting so much I decided I couldn't be confident of any change.

Unfortunately because it was an auction purchase I have no way to contact previous owners to confirm if the ECM was remapped so that's good news that this can be looked into Mike. Thanks! This might be a route to go down soon.

Does anyone know the resistance to send a test signal to ECM from knock sensor?

If you think it has a steady vacuum leak, spray some carburetor cleaner around the mating surface for the throttle body (if you can buy it in an aerosol can). If it changes the RPM at all, you have a leak.

You should see a change in the timing advance when you tap on the knock sensor with a piece of wood or metal. You can also hit the large cadmium-coated part of the motor mount with a hammer.

If you still have the original MAP sensor, look for the part number on the body- they used text that looks like it was done on a dot matrix printer, usually yellow (it's not bright yellow, but it should be visible).

[SenselessSteve]

Thanks JimN. Your status is already legendary here in Ireland so if you're ever over here, I'll be the first to buy you a pint of Guinness (irish stereotypes permitted)

The part number folrom the MAP that came with the boat is 876 4133 although I'm almost certain it's not the original (strange brown colour - no dot matrix print)

I tried carb cleaner along all possible leak sites and unfortunately didn't walk away any wiser.

I'm considering taking the inlet manifold off to get it pressure tested but would like to see if there is any knowledge circulating on what the LPG conversion butchers do to an ECM (if anything). I thought that their systems simply used the standard signals for Proportionate calculations for LPG. (Been wrong many times before though).

Any of you guys ever encountered this conundrum ??

All help truly appreciated

[JimN]

Thanks JimN. Your status is already legendary here in Ireland so if you're ever over here, I'll be the first to buy you a pint of Guinness (irish stereotypes permitted)

The part number folrom the MAP that came with the boat is 876 4133 although I'm almost certain it's not the original (strange brown colour - no dot matrix print)

I tried carb cleaner along all possible leak sites and unfortunately didn't walk away any wiser.

I'm considering taking the inlet manifold off to get it pressure tested but would like to see if there is any knowledge circulating on what the LPG conversion butchers do to an ECM (if anything). I thought that their systems simply used the standard signals for Proportionate calculations for LPG. (Been wrong many times before though).

Any of you guys ever encountered this conundrum ??

All help truly appreciated

Unfortunately, it's extremely expensive to convert a car, truck or boat to LPG in the US. Is yours still running LPG, or are you back to gasoline? If you're using LPG, I wonder if the jets are the wrong size.

I'd like to get over to that part of the World- two of my ancestors came to America during the third English Civil War and I'd like to see their old stomping grounds.

[SenselessSteve]

It's back to Gasoline Jim. I think the tank line and jets were all removed as donars for another boat. I thought it would be simple to convert back by plug welding the 8 gas inlets in the intake manifold. Unfortunately it hasn't worked out that way though.

Is there any books/manuals where I could get a part number for the MAP sensor as I'm sure the sensor that came in the boat isn't an original.

All 8 plugs are fouled identically so i'm back to either vacum or ECM.

Id love to welcome you to this part of the world. :-) I'd gladly exchange some proper Irish hospitality for someone with the skills to get this old girl singing again.

I'm going to spend tomorrow back in the garage trying to make one last push before I buy you your tickets

[mikeg205]

ECU for sale on ebay

http://www.ebay.com/itm/MEFI-1-ECU-F...p2056016.l4276 - could be reflashed...

here are some automotive parts to cross reference.

Indmar 5.7 TBI non – vortec
Starter
Delco 6562N

Fuel Filter
Napa 23481 or 3481 (gold) or Equivalent
Added inline before fuel pump Napa 3003


Oil Pressure Sender
NAPA SME 185899

Fuel Relay –
Napa AR153SB
Standard Motor Products - RY282

http://www.standardbrand.com/online%20catalogs-ecatalog/content.aspx

5.7 TBI Throttle Position Sensor
Napa MPF 329920
Standard Motor Products - TH42
IAC –Idle Air Control
ACDelco – ACD217429
SMP AC6

Map Sensor
2503679 1 bar MAP sensor
Delphi DEM PS10082
Napa Eichlin CRB 216865

Standard Motor Products AS4

Knock Sensor
Napa DSK 206
Standard Motor Products KS3
Fuel Pump
Napa P60987 – Low pressure
Napa P60962 – High Pressure
Distributor Cap - HEI
Napa Cap PE RR249SB
ROTOR - HEI
Napa Rotor – MPE RR250SB

[JimN]

Does it idle poorly, or is it relatively smooth? Assuming the exhaust smells of unburned gas, try this- unplug the MAP sensor tube and listen for any changes in the idle speed. If it changes, that's good. If not, check for vacuum at the end. If it has none, find out why.

If you have a multi-meter that will measure voltage and resistance, insert stick pins or T-pins into the wire side of the silicone seal on the MAP sensor wires, sliding past the seal and making contact with the terminals. Bend them so they can't touch each other. Use test leads with alligator clips and attach them to the pins.

Measure the resistance between the MAP sensor ground and ECT ground- IIRC, they share the same ground point and wire to the block. Measure the resistance to ground from the MAP sensor plug's ground terminal and also from the ECT's ground terminal- if you see more than about .1 Ohms, it's too high. If this checks OK, clip the ground lead of the meter onto a good ground on the engine block.

On the MAP sensor plug, Gray is control, Lt Green is the return voltage wire and Black is ground. The Gray should have ~5VDC at all times and the Lt Green should have a range of just less than 1VDC-4.5VDC. At idle, you should see about 1VDC on the Lt Green wire. If it's higher, or the Gray wire doesn't have ~5VDC on it, there's a problem. If the Lt Green wire shows higher voltage, it's telling the ECM that the engine is not at idle- low vacuum means the throttle is open, which requires more fuel. Low vacuum=high voltage=open throttle and since the MAP senses the vacuum below the throttle plate, this is critical.

With the key ON/engine OFF, measure the reference voltage on the Gray wire, using the pin in the ground position and the Lt Green wire should have high return voltage because there's no vacuum. Connect the vacuum gauge to the MAP sensor and pump it a bit- you should see the voltage decrease as the vacuum increases. You may not see much needle deflection on the gauge. If you never see needle deflection or voltage change, it's possible that the sensor is bad. If you have a GM parts provider, you could ask for the large, 1 Atmosphere GM MAP sensor. They also have a small one- this is used on the LTR and inserts in the manifold, so it won't work. The TBI and LT-1 used the same MAP sensor.

[SenselessSteve]

Thanks Mike. That's a great help. I'll order the MAP now.

I see there's an MEFI 1 ECU on the UKEbay also. http://m.ebay.co.uk/itm/381006821572?nav=SEARCH

I'm not sure if there's anyone here who could reflash so might have to send to the states. You don't suppose it would be possible that this one would be plug and play?

[mikeg205]

Thanks Mike. That's a great help. I'll order the MAP now.

I see there's an MEFI 1 ECU on the UKEbay also. http://m.ebay.co.uk/itm/381006821572?nav=SEARCH

I'm not sure if there's anyone here who could reflash so might have to send to the states. You don't suppose it would be possible that this one would be plug and play?

depends what it came out of... might work... would be great to confirm which boat it came out of.

[SenselessSteve]

Thanks Jim. I'll follow these steps tomorrow when I get back to the garage.

The idle isn't so bad although you can certainly hear the characteristics of too much fuel (in that it's doing it's best to combat the rich mixture).

When you say unplug the MAP sensor tube, do you mean remove the MAP sensor from the top of the intake manifold? (Where the small pipe inserts at the rubber seal?)

[JimN]

Thanks Mike. That's a great help. I'll order the MAP now.

I see there's an MEFI 1 ECU on the UKEbay also. http://m.ebay.co.uk/itm/381006821572?nav=SEARCH

I'm not sure if there's anyone here who could reflash so might have to send to the states. You don't suppose it would be possible that this one would be plug and play?

The only way to know for sure is to read the Checksum. If someone over there has a Tech1 with the marine card or possibly a Mercruiser/Volvo-Penta diagnostic computer, they should be able to do this. I connected our Tech1 to a Mercruiser and although I couldn't operate any functions, I was able to read some data. I have to think someone in a car/boat club has one, or if you have Malibu/Supra/Moomba dealers, they should be able to check this, too. For that matter, they should be able to read your data to see if/where a problem exists. If the numbers don't match what they should see, it's easier to diagnose problems than using a multi-meter (the sensor return and Battery voltages show on the screen).