mark kibort

I havent been able to sleep well knowing that my 928 brother has not seen his 928 run in a couple of years, so i went over and we attacked it today.
We knew it would be tough , due to the 928 5 liter part euro motor being void of the cold start circuit. after the starter drained the little battery, , we ended up towing it behind his truck in 2nd gear. that way, it would get oil pressure, electrical would be fed,and if it was going to start, this would be the best way. ..........well, it didnt even kick or bite at all. nothing.. pure just compression braking, no heartbeat.
we gave up after about a mile of in and out of gear, cycling the ignition. seeing the voltage up normal... oil pressure normal , RPM in the 1400rpm range....... but nothing.
so, in the driveway, we did the normal tests. tried to see if there was spark. didnt look like any when plug grounded to the cross bar bolts (maybe bad ground for plugs) coil sounded like it was arcing, but voltage on the coil was around 4-5 volts (is that normal as measured on the positive and negative terminals????) . i noticed that the fuel pump wasnt cycling, so i jumped the fuel pump relay..... the pump could be heard, so we jumped the battery with his truck and started to run the starter... I then cracked the fuel line, fuel dribbled out.. didnt seem like much pressure , but forgot my fuel pressure meter to check that.... anyway, .. i was checking spark again and it started to catch.. i put the plug back in and it started to run... unreal! it was alive! we got it to operating temp and then, put the fuel pump relay back in to see if that was the issue. nope, it ran fine.. So, we started doing laps around the neighborhood. it ran great, power, smooth, etc.......

Now the question .... what changed? my theory is that the pump didnt run long enough to get fuel in the lines that might have been void of fuel..... but that seems odd because we have been able to start the car after rebuild and have it fire right up ....so, i have no clue why we could bumpstart , in gear for a mile with no hint of running, but messing around in the driveway, suddenly it starts. maybe pulling the fuel pump relay jared something in that relay as it is a little different than the S4 set up, with more electronics in the relay that could be intermittent.

good news , its running and willl be raced next season hopefully, but until then, it would nice to understand what the issue could have been. we are also installing the cold start system as we found it in his box of parts and should be an easy install. just going to duct the cold start into an open port to the euro plenum by cutting the dual feeds to the US head intake ports.at the back of the heads and putting a hose on that and connecting it to the plennum. ( the cold start components, contains the cold start actuator and the cold start injector )

any ideas what might of changed to cause the car to finally come to life??

John Speake

What type engine ?

mark kibort

It's the 5 liter i built up out of a 4.7L euro block, bored out to 5 liter. (long story......... we ended up using a used, spun bearing 4.7 euro block, bored it, put in a new crank. new bearings , welded up the top of the cylniders due to some deterioration, decked it, and put it together.

equiped with the euro 85 intake modified to accept the AFM of the 82 928 Ljet system.
euro heads
headers single 3" exhaust
85 5speed transmission
2900lbs with driver
290rwhp

GregBBRD

Although I'm 99.9% sure you will disagree and want to argue about it, I'm going to go out on the ledge and say the problem was either spark or fuel.

mark kibort

Greg.. Now that is quite enlightening......let me enlighten you and maybe surprise you as well. I agree.

Now, to try and figure out what could have changed during our efforts, can you offer some ideas? we only messed with jumper cables, turning on and off the ignition switch, and jumpering the fuel pump relay , but when running, it seemed to function fine. the battery was weak to start, but when bump starting it, the voltage was 13.5. no bite at all. just dead .... fuel pump was cycling when the engine was turned over, and then we would stop. (that characteristic "buzz" short term)

on the Ljet cars, is the voltage that would be measured at the coil be only 4-7 volts? could the reason i didnt get a spark on the spark plug when it was being turned over , via jumper wires, was because chassis ground doesnt really equal engine ground?

GregBBRD

That is normal coil voltage for a car with ballast resistors...actually a bit high. Just make sure you have the proper coil for that set-up.

Really tough to start an L-Jet car without a cold start valve. I'd start there, get it hooked up, and see how it starts the next time.

mark kibort

Thanks.... you are probably right there . the only other thing i noticed was , when i was checking fuel pressure, that the fuel dribbled out, rather than sprayed after fuel pump was cycling. when i loosened the fuel rail nut. but maybe its because it has that little ball bearing in there. thought it might not have any fuel pressure.

what is the sequence for the Ljet to function? it has to have spark, otherwise, the fuel injectors dont fire?, or is it the other way around. you need fuel injectors to be firing or the spark doesnt work.?
anyway, thanks for the info on the coil.. just checked my notes it was 6 volts when it was running ant about 4 when it was trying to start. its the stock coil, so we should be good there. (aha ha. ballast resistor)
yep, it has always been a huge pain and a source of frustration to start this thing on a cool day. looks pretty straight forward to hook it all up using the method i used on my old 5 liter part euro.

I just cant understand why when we were dragging this car in gear, to bump start it, why it didnt show any signs of life. either fuel was not reaching the engine, maybe that fuel pump relay was being finicky.
thats all i can imagine.

does anyone have any pictures on how the cold start is modified and connected? i might have been the only one to do it, and Rich had my old 5 liter and i think its been sold yet again since then.

mark kibort

So, i guess, ill cut off the two outlets that go to the heads and put a hose on that , and duct it too the top of the plennum below the runners there is an unused 1/2" port.

on that Regulator "thinkgy" (the silver thing that opens during the cold start sequence to allow air to flow from the air filter side of the TB) does that need to be connected to anything or can i just put a little mini filter over the inlet?
(EDIT) I think it needs to be connected to that port on the bottom of the "U" , so that it is getting fed Metered air by the AFM.(otherwise it might just be an intake air leak, unmeteed , and might not work as well..

i found the electrical connections that were tied off , so they go to that silver thingie and the cold start injector.

I just cant remember anything but cutting those two pipes that go to the heads and putting a tube on it and feeding it to the intake . that i remember.

James Bailey

I recall that later Euro 2 valve heads the ports on the back of the heads actually feed into the exhaust ports and NOT the intake. So a functioning cold start ends up shooting fuel into the exhaust....... I would probably just put the 1978- 79 CIS style plenum mounted 9th injector on with a momentary contact switch inside the cabin to prime the engine for cold starts.

mark kibort

Actually, i found this out before i started my 5 liter project back in 2000. yes, if you leave those two opposite pointing, horizontal tubes in place and mount them to the back of the euro heads, you might have a fire breathing dragon.. (gas added to the exhaust ports cant be good ) SO, what you do, is cut that off at the merge point........ and put a hose on it and port it to the intake plennum. ( i did this with the first 5 liter part euro) i just forgot where the intake to the cold start actuator, goes. there is a port at the bottom of the plennum that feeds the "u" , i think it goes there. that way , it gets metered air on cold start.

all the stuff is there, may as well use it. you need air, not just fuel so, as i remember, it worked REALLY well. still with stock function, but not feeding air into the intake ports, but feeding it into the intake itself.

mark kibort

FOUND IT ! the hose from the cold start actuator, just connects to the base of the "U" as stock.... scot has a hose on it right now that has been clipped and a ball bearing has been inserted. maybe we got lucky and its not "clipped " if it is, we will have to make a new one or get a new/used one from 928intl.

next , you can see the picture installed . the hose comes up from the base of the plennum and attaches to the cold start actuator.
so, the only mod we need to do is to cut the feeding air and fuel tubes and put a single hose on it and feed it to the plennum. (euro has a port under the #2-3 runners)