Vapor Lock?

The car starts and runs fine from a cold start. You can drive as long as you want and everything is normal. When you shut down it will re-start up to 15 minutes later. After that, it just turns over and won't fire off. I have confirmed the ignition is working correctly. While it was hot and not starting I pulled a plug and observed the plug fireing. I've confirmed the fuel pump is working by removing the airfilter with the ignition switch in the on position lightly pressed down on the air induction valve and heard the fuel pump come on. Im begining to suspect a vapor lock? The temps are in the 90 degree range down here so once you run the car and shut down, its gets pretty hot under the hood. About a week before this starting happening, I installed a new set of plugs NGK BP6ES gapped at .025 as recommended from factory specs. I drove the car 2 or 3 times before this started. Could this plug be part of the problem? I can't imagine why but I didn't have a hot startup problem before? Im not sure where to go next and am open for suggestions. Joe

 

I'd suspect a failing pump before the plugs, I run one range hotter on my carbed cars in that same brand...

I think the injected pump has an integral valve, that maintians pressure?

A failure of that would air lock the line maybe?

 

Sounds familiar..............Check the accumulator outlet (The hose coming out the back of the accumulator going to the top of the Left fuel tank), if there is fuel in there then most likely you have a leak in the accumulators diaphragm which holds the pressure in the system. also may be one of the check valves. I had a similar problem recently.

-Darren

 

Pitts, I am having the EXACT same problem as you and have narrowed it down to a leaky-bad accumulator. I have one on order and should have it in by Thurs-Friday and will post test results. Just search "fuel accumulator" for diagnosis and removal. One guy even has a diy with pics.

 

Here's another one from a thread I found. It looks like there is no easy answer for this. There are several things it "could be"? Joe

Hi Lawrence1 I have a 1980 308 GTSi #33393 and had the same problem earlier this summer and here's what I did to fix it. I first I put in a new fuel pump (original one still in so I thought I'd try here first) didn't help as I thought but wanted to put in a new fuel pump anyway. Then I put in a new fuel filter and fuel accumulator, still didn't help. Then I put in a new warm-up regulator and bingo problem fixed. So, if after your trouble shooting nothing works replace the warm-up regulator. Good luck and let me know how it turns out. Pauly

 

True...But the smokin' gun (hopefully) for me is that the accumulator is leaking fuel from the accumulator vent....Fingers crossed.

 

Last night I ran the car till it got hot and parked it for an hour. Would not restart. I tried to floor the gas and let the engine spin for about 20 seconds. Still nothing. I removed the air filter and with the ignition switch on, pressed the baffle down about 1" for about 5 seconds and could hear the fuel pump run. Walked back to the drivers side and the car fired right up? So...there's something going on right there at the fuel? THe safety switch "MUST" be working because it triggered the pump when I pressed the baffle down. Could the car not be drawing enough air on a hot start to trigger the baffle to open? I'm considering replacing the safety switch but either it works or it don't? Am I missing something? Joe

 

Hey Pitts. Well, I'm happy to report that my hot start problem is fixed and it was in fact the fuel accumulator. Do yourself a favor and check yours.....it is very easy to check as mentioned by a previous poster. Just remove the vent line from the rear of the accumulator and check for fuel...it's that simple. The accumulator is the canister right next to the fuel pump. This is the easiest fix I have ever done on this car.

 

I've been silently ovbserving this thread as my 1980 400i has the same symtoms..my system is exactly the same as the 308's (X2)..thanks for the help..Where to buy the accumulator since it's simlpy standard Bosch..what is the part #..thank you so very much..p.s...the 308 forum has saved my bacon for years..thanks guys..Jacques..

 

Got Mine from T Rutlands. http://www.trutlands.com just type in accumulator in the search or just call them. I replaced my fuel filter while I was at it and had the tanks drained.
-Darren

 

Hi Guys, I'm taking the car over to Kelly (about 45min away) on sunday and were going to put it on jacks and check the accumulator. He's got the same issue and its his accumulator too. I disconnected the electrical connector at the warmup regulator and the problem went away...sort of. Now I have to spin the engine with the gas floored to make a hot start. But at least it will start! I am suspecting the accumulator as well and will find out for sure on Sunday. Will keep everyone in the loop. Joe

 

Update: Sunday I took the car over to Kelly's. We changed the oil, trans and brake fluids. We got some really ugly brown brake fluid out of the system. While up in the air we did a good visual inspection with the normal gigs found. Kelly's impression is that its a solid car which goes a log way. The fuel pump and accumulator were checked ok. After we put everything back together we took it for a ride and got it hot. Parked it for about 30-45 minutes and it would not start. We tried disconnecting the cold start system and with the gas floored it still would not hit a lick. NO gas smell so it's not flooding? We pulled the air filter out and with the ignition switch ON..pressed the bellows downward about 1/4 inch for about 5 seconds. Hit the starter and it fires right up? It's obvious its a fuel system problem but I have no idea what to do to try and trouble shoot. Cold starts are normal so I'm still not convinced its not a vapor lock? Anyone with experiance with these (1980- 2v) fuel systems have any suggestions? joe

 

How did you guys come to the conclusion that the fuel pump and accumulator are okay? If you didn't check fuel pressure with the engine running and fuel pressure after "X" number of minutes with the (hot) engine off I would not say you made a conclusive test.

On another note..... if the brake fluid has been neglected (sounds like it has) I would assume the coolant has also been neglected. If you don't know when it was changed last I would change it now (before the price of anti-freeze goes up again!!

 

Next time this happens try removing or unscrewing the gas cap. It should start right up... I think.

 

Got the new accumulator in and installed last night. Its a pretty simple installation from under the car but it didn't fix the hot start problem. I'm losing pressure somewhere so it looks like my old accumulator was OK. While under there I could see where some fuel has leaked from one of the bottom fuel filter fittings. Over time it has discolored the fuel line just below the attachment fitting. I was really hoping the accumulator was the problem but now I'll go to plan B. I may look at replacing the filter setup with a single filter design. Any recommendations on that? Anybody needs a good used accumulator send me a PM. Bah humbug!

One thing for sure....if you get stranded with a hot start and suspect a vapor lock this works for me every time. Remove the air filter and with the ignition key on, lightly press down on the round plate at the CIS inlet about 1" for about 5 seconds. This opens up the fuel system and pushes the vapor out and fuel in. Replace the filter and start it up. THis works for me every time on a hot start. Joe

 

I contemplated changing to a single filter when I re did my fuel lines, filters, etc. I had a local shop re build the old assembly like new and until I had it installed...just right..it had leakage. The fittings must be very clean and tight to be sure it won't. If the overall condition is good I would remove it and clean then reassemble it. If that doesn't work for you you will need the larger QV filter to do the job, not a single from the early FI system.

And...if you have this type of leak so close to the exhaust system...do not drive the car!

 

Bummer. I suppose it could be your fuel pump check valve. Go to autohausaz and it is the same as the 76-79 MBZ 450SL.

 

Thought I'd give you guys an update. After chasing my tail a while, I decided I needed to get a set of gauges on the CIS to see what was going on. I had no doubts it was vapor locking. I called a couple of local shops that work on Benz, Jags ect ect and got quoted 1 hr labor (at $60-$110 per-hr) to give me some pressure readings. So after surfing the web for a bit, I came across a set of Bosch CIS gauges for $99. They also had the Haynes fuel injection 1978-1985 CIS repair manual for another $20+. Anybody else interested here’s the link on the gauges http://www.autorepairmanuals.biz/site/573683/product/STRTU447PB and the manual is Haynes #10215. The box arrived about 1 week later. I read up on the CIS a little and made a few calls to Larry Fletcher who is the “Master Ninja Guru” of Bosch CIS systems. I connected the gauge to the fuel distributor as directed by Larry and checked the fuel pressure. It was around 70psi (or 5bar) with the pump on which is good fuel pressure. Once the system is pressurized it should hold some pressure long enough to let the engine cool down and prevent vapor lock. Mine held pressure for about 3 seconds after turning off the pump! I mean it went to ZERO before I could turn off the key and walk to the back of the car! I have no fuel spraying out anywhere so the fuel is obviously going back into the tank. At Larry’s suggestion, I first checked the fuel pressure regulator which is on the fuel distributor and easy to get to. Don’t confuse this with the fuel accumulator under the car. If the seal is bad, the pressure regulator will allow the fuel pressure to drop rapidly through the fuel return in the fuel distributor. The regulator checked ok. Since I had already replaced the accumulator there was nothing else left but the &^%$$(* check valve. I jacked up the car and removed the external check valve and “presto”. I could blow air from both directions through the check valve. I “whopped” the hell out of it with a 17mm wrench and it started working again. This check valve is not the correct valve for the car and looks like something for hydraulics. I’m not sure how long its been this way and they used rubber hose and hose clamps to make the short connection between the fuel pump and the accumulator. It struck me odd when I installed the accumulator and I guess I should have given it more attention for safety sake when I first saw it. You guys need to take a look at this on your car because I don’t know how long that rubber fuel hose or clamp would last with 70psi of fuel pressure in there. If that sucker blows out, you’ll be spraying raw fuel on your exhaust. So… I ordered the correct external check valve kit from autohausaz.com for $21.53 (bosch part # 1-587-010-003) and I’ll build the correct hard tubing with banjo fittings to make the connection as it should be made. When it’s all said and done, I’ve spent a little less than $200 on everything, I’ve got my own set of gauges now for any future fuel trouble shooting and the best thing is that I got a good education on how the CIS system works.

 

Not to mention you've likely saved your pride and joy from a nasty fire waiting to happen.
Excellent outcome imho.

 

This will be my final post on this subject. The correct check valve came in and I built the correct connections for the install. Once verything was back together I powered up the fuel pump and the fuel pressure went to 72psi. Once the system was pressurized, I turned off the fuel pump and the pressure dropped to 43psi. I let the car set while checking the pressure every 30 minutes and looking for any leaks. After 2 hours the pressure was still at 40psi and no fuel leaks were detected. I couldn't stand it any longer so I fired up the car and drove it hard for about 15 minutes to get it good and hot. I parked it and let it set for 1 hour which was usually when it would be vapor locked. The car started right up in less than 1 second! What I did notice is NOW there is an obvious difference in the start up time, cold or hot. Previously (with a faulty and gradually failing check valve) I had to grind on the starter on a hot start for 15-20 seconds before the car would fire. Now it's less than 2 seconds on a hot start! So...I am making an assumption that if you find your starter time getting longer, it could be an indicator of fuel pressure check valve problems? Lastly...I want to thank Larry Fletcher from Fairhope Alabama who is the CIS fuel system top expert who spent several hours on the phone with me helping to trouble shoot and giving me part numbers to order. If you've got an overhauled CIS on your car, odds are Larry re-built it! You guys keep that name handy for future reference on the CIS system. I drove the car to work today. It's 96 degrees today and no hotstart problems. Yipppeeeeeeeee! Joe

 

Joe, Your coming to my house to help me with mine WHEN?????????

Kelly

 

Kelly, I may be going to the big easy on Sunday. If I do, I'll give you a buzz and we can throw the pressure gauge on yours. We'll know in about 10 seconds if you've got a leakdown. Joe

 

We're leaving the house about 10:30 to go on a drive if you would like to join us.

 

At 4 min in video fuel percolation start at 45 deg