rufrob

Hello Rennlisters.
Thanks for all your help in the past,
My rebuild is done and now I have a 3.4liter engine. However I have been having some starting and running issues. It floods. I have to remove the fuel pump relays and crank it for it to start. Sometimes if I am quick I can reinstall the relays before it dies. I have replaced the fuel filter, spark plugs, injectors (from the 924/964 turbo), adjusted the base idle and CO mixture. Now sometimes it will start first try in the morning and when the engine is warm it will restart up to 1 hour after shut down. When the engine is cold idling is smooth, but hesitates and misses when driving. As it warms up it goes away and drives well.
Since the overhaul I have only driven around town, no highway.
Some back ground: my pistons showed signs of burning, ie pitting.
I had fuel tank issues caused by peeling POR15, but since then I have replaced the tank with a very clean used tank from a 1988 Carrera and have replaced both fuel pumps and rewire the pump circuit in order to get direct current to each pump individually.
Once I had a similar problem but it was due to pumps not coming on due to slightly burnt relay sockets. But now both relays click and I can smell the raw fuel soon after cranking.
BTW fuel accumulator was changed about 2 years ago.
Any ideas?

Mark Houghton

Thermotime switch/cold start valve malfunctioning??? That would inject raw gas, ordinarily needed just for cold starts.

rufrob

Good point the thermotime. Come to think of it the wiring connection at the switch is poor at best. It keeps falling off. I will check it tomorrow. thanks,

rufrob

I will get some pics up soon. Thanks Mark. You were correct. Simply disconnecting the thermotime switch made the car start. I swapped it for a used one and now she starts albeit belabouredly. Next issue is the long cranking, hesitation during mid-range acceleration and slight run-on which were not there before the rebuild. Any hints?

rufrob

Update. The problems started a year ago when the POR 15 began to peel, wreaking havoc with my entire fuel system. I got a super clean used tank from an 1988 Carrera. Then I did the overhaul due to smoking and oil leaks. Now I have a 3.4 with 924/964 Turbo injectors. I sorted the flooding and hard start with a new thermotime switch and much of the hesitation by changing the fuel filter, rear pump, and cleaning (as best I could) the fuel accumulator, WUR and the fuel distributor head. The latter having the biggest impact. But its is still there. Idles fine and delivers truly biblical power. I set the timing and c/o but have been playing the c/o to address a very slight knock under boost past 4000rpm. The Brazilian coil is 2 years old, and CDI works well.
The hesitation start at about 2000rpm, is intermittent and worst when cold, but more regular when the car is warm. Its driving me nuts. Plus I am afraid of damaging my fresh rebuild, since the last rebuild was partially due to running too lean.
I don't know what my compression ratio is and am using the stock intercooler and fuel pump.
Any ideas?
I was going the try the 044 fuel pump next, but shouldn't it be mounted in the rear and not the front?

Thanks and cheers,

Rob

Oilonly

044 BOSCH MOTORSPORT (ref 0 580 254 044) in front of the car rufrob.

Dave 86 930 Fl

What have you done wrt the WUR? Has it been opened and cleaned? How about fuel pressure, have you set cold/hot pressures? I would suggest sending it off to Brian Leask and get it updated to match your build.

Regards, Dave

rufrob

Update. I figured out the problem. After swapping the front pump to see if anything would change my mechanic decided to recheck the C/O and HC. The H/C was crazy high. We rechecked the timing to find the apprentice set it incorrectly. Surprisingly it could run. Reset the timing and the engine was so smooth, and the exhaust sounds like its making popcorn. Now to take a highway run to "clear the carbon".
Anyone has a big intercooler? Thanks everyone!!

Einsteiger

So glad to hear everything turned out well and that your rebuild was not compromised. Now for a little theraputic highway time!

rufrob

Well, I took the girl friend home at 1 am on the the highways which traverse Tokyo. The engines didn't feel as responsive and free spinning as it did before, but at least the miss and hesitation is gone. When "cleared the carbon" however, there was no carbon to speak of, no cloud of black smoke which was present before. She, the car not the girlfriend, felt planted and pulled, ahh pushed, strongly, no knocking or pinging. I am afraid to floor it but even so my girlfriend read out 230kph-ish. I boosted to get up to speed then could cruise at very little throttle and little boost, below 180 she is running on vacuum, again car, not girlfriend. On the way back I am sure I hit around 240 but I dare not confirm this as the horizon comes quite immediate. Lowering the front suspension greatly improved stability, but I have to live with scrapping the front spoiler getting in and out for parking lots.
I have never driven nor heard a 3.4 before. At idle the engine has a distinctive dah,dah,dah,... sound. Not a miss, the idle is smooth, the c/o and h/c are bang on. Is that sound normal for the 3.4?