308 QV hot starting problem, new

My 1985 308 GTB QV won't start when it's hot. When cold, it's fine. If I warm it up, drive it, and leave it for, say, 1/2-1 hour, it won't start. Cranks quickly, but won't fire. If I open the engine cover and let it sit for an hour or two, it will start and run fine. Any ideas as to what could cause this? (cycling the key several times does not help it) Thanks, in advance, for any help and suggestions.

 

Most likely, your car is losing the residual fuel pressure after engine shutoff (it should stay at about 3 bar for 20 minutes). Three possible causes (and usually investigated in this order):

1. Bad accumulator -- check to see if liquid fuel is leaking out of the vent nipple on the end. The US cars have a hose on the vent nipple going back to the tank so it's not obvious (and you need to remove the hose to check). On the euro cars, the vent nipple is left open to atmosphere so any liquid fuel is obvious (and dangerous).

2. Bad outlet check valve on fuel pump.

3. Bad o-ring in pressure regulator section of the fuel distributor.

Do some searching on those kind of terms for prior threads.

 

Steve, thank you! We'll check those things out tout suite.

 

Try a hot start with the throttle open. It could be flooded from the injectors leaking

 

Most likely culprit - Fuel accumulator.

 

Thank you all! I did try it with the throttle open; didn't help. I also tried cycling the key several times, which did not help either. The FI system is a K-Jetronic; we think it might be the fuel accumulator, or the fuel pump check valve, as noted above. Working on those.

 

I think the fuel is rich , How about adjusting with a 3mm hexagon?

 

We have not done that. But until this problem, the engine has run perfectly and the plug color has been fine. The present problem is solely one of the engine not starting when it is warmed up and then shut off. If I let it cool, it will restart. And the concensus among knowledgeable folks here is that the accumulator is the first thing to check out. We are going to get it on a lift and see if the accumulator is leaking internally; if it is, we'll replace it and see if that solves the problem.

 

For clarification: how hot is hot? Will it start 1min after shutdown? The checkvalve and accumulator are considered "warm start" issues. Like 15min-2hr.

There's a fuel pressure tool you can use to test the CIS system, and it isn't expensive. It will tell you if you are loosing pressure too quickly.

There will be debate, but Rifledriver indicates that the accumulators are usually blamed but rarely fail. My personal experience backs this up. My warm start issue was the check valve. I believe rust particles inside the tank(probably from the sending unit) appear to have kept the valve from closing. I added a fuel filter between the tank and fuel pump, when I changed the valve. I could see some particles in the fuel, so wanted to avoid this issue a 2nd time.

There's also a ton of info on this very common issue if you look in the archives. Sounds like a pretty standard case. Let us know what happens.

 

postscript maybe it's sucking air from somewhere.

 

Do you have details about the filter you installed?

 

If I wait five minutes after shutdown, she won't restart.

It looks like the accumulator is leaking- pulled the hose off and fuel ran out. So I ordered a new one and we should have it in by early next week. I'll report back.

 

Sorry, Rod, I don't remember exact details of filter(did that mod 10yrs ago), and 308 isn't on the lift at this moment so can't check. It wasn't an idea I came up with, but rather something someone else had already done in a thread just like this one. What I do remember is that it was from summit racing, inline style, aluminum case, with replaceable filter, and the end fitting size either matched our fuel line, or I bought threaded adapters to match it to our lines. I think just about any fuel filter would work. I did hang it on a bracket, though I think it was small enough that it would have probably done OK, just hanging on the fuel line.

Even though our tanks are aluminum, they have some steel parts in them, like the sending unit, so I think everyone is likely to have rust particles in their fuel system. The location of the factory filter keeps stuff out of the engine, but not out of the components before the engine.

 

One more to add to the list:

4. Leaking fuel injectors

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No, I can't agree much with that -- on K-Jet/KE-Jet, the slits in the fuel distributor are fully closed when the airflow metering plate is not deflected (i.e., when the engine is not running nor cranking) -- let me think about that some (but if the entire fuel volume of the Accumulator could discharge out a single leaking injector = I think we'd have a lot of reports of fuel hydrolocking and engine destruction).

 

We'll have to agree to disagree on this one . First off, Steve please know that I have the utmost respect for you and your expertise. Having been a member here for the last 17 years and reading your posts I suspect that you have likely forgotten more about these cars than I will ever know. That stated, I've been working on Bosch CIS systems for over a decade, and I can confirm that leaky fuel injectors in isolation can indeed be the cause of hot start abnormalities. You are completely correct that at engine shut down the airflow metering plate will be at its resting position and not exerting any movement on the distributor control plunger. As such, the distributor metering slits will be closed and there will be no movement of fuel from the lower chambers to the upper chambers of the distributor. That stated, if multiple injectors are leaky, the remaining pressure in the upper distributor and fuel lines can discharge residual fuel into the intake manifold resulting in challenges upon warm restart. Note that when performing fuel pressure analysis for hot start diagnosis, problems with items #1-3 (described in your post above) will result in abnormal residual fuel pressure readings while leaky fuel injectors will not. Sometimes this can help with narrowing down the issue to the injectors. Attached is the Bosch Kjet trouble shooting guide that calls out injector leaking as a potential cause for difficult warm starts.

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Apologies, I should have been more clear when I added 'leaking fuel injectors' to the list of items to consider in post #2. Specifically, leaky injectors should be considered on the list of items that can cause warm start issues on CIS cars but generally are not a cause of loss of residual fuel pressure in isolation.

 

I'd believe that a couple of leaking CIS injectors on a 4 cyl. could cause warm restart difficulty, but one leaking injector on an 8 cyl or 12 cyl? No problemo

 

Agreed!

For reference, the two scenarios where I have encountered leaky injectors contributing to warm start issues both involved 3x8 cars. For one of the cars I thought we had easily sorted the issue after finding an abnormal residual pressure in the setting of a failed fuel accumulator. Replacing the accumulator corrected the residual pressure abnormalities but not the warm start challenges. I pulled the injectors and found 7 of the 8 injectors leaked badly. After servicing the injectors and confirming resolution of the leaks with an injector tester the warm start issue was corrected. The other car had normal residual pressure on initial fuel pressure testing. All 8 injectors on that car were leaking, with 6 of them having wide open leaks and terrible spray patterns.

I do a lot of work on CIS injectors and not surprisingly the low mile garage queens with original injectors have the highest likelihood of poor spray pattern and leaks. The same steel Bosch CIS injectors are used in many older Mercedes models and it's not infrequent that I find original injectors from 150k+ mile Mercedes that are leak free with excellent spray pattern. Many folks like to toss the old steel injectors, but they definitely can be rehabilitated with ultrasonic cleaning coupled with specialized back flushing techniques while maintaining the injector pintle open.

 

That's a lot of leaking going on . Since the V8s will usually fire up on a single bank, that makes good sense that it would have to be more than 50% of the injectors leaking to have a warm restart problem with good residual pressure. In fact, I can't recall a single time someone posted here that "the residual pressure is fine, but I still have warm restart problems", but maybe the vast majority of DIYer who post here drive their cars enough to avoid that condition developing. Were both of your examples seldom-used, super-low-mileage Garage Queens?

 

Low mileage, yes. 'Garage Queens', debatable . A 308 QV and a 328, both driven less than 100 miles per year. the 308 was immaculate, the 328 was not well taken care of.

 

Just a follow up to this problem: it WAS the fuel accumulator, which we replaced with a new one. In addition, we were able to buy the Bosch paart for less because of a post here on Fchat with a crossover number to (I think) a Mercedes Benz part. These CIS systems were fitted to quite a few cars and parts like the fuel accumulator are evidently common to many of them.

Much appreciation for all the help on this forum!

 

One pleasant surprise when I got my 328 was that the fuel injection system was the same as several older European makes I worked on in the 80s and 90s. There are a few customizations to fit the engine bay but otherwise it's exactly how I remember from back in the day, and most parts are generic, reasonably priced, and easy to source. There is good documentation from Bosch online as PDFs. So even with an average understanding of Bosch K-Jet I still feel like I can fix at least one part of the Ferrari with some level of competence! The rest of the car will be a learning experience.

 

Thank you for sharing the follow-up and congratulations on resolving the issue! Wishing you many miles of trouble free diving ahead.

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