Rough running when hot

#1

My gasser runs rough for the first several seconds when the engine is started at operating temperature (180-190F) It seems to get worse if the engine is hotter and it dosent have this problem if the key is put in the ON postion for a minute or so before cranking the starter.

Am i looking at a thermo-time switch problem because of the cold start valve firing when the engine isnt cold.

I sorta want to get this problem fixed because the engine would stall if it has any load like the A/C compressor, heavy alternator load or being put into gear.
Sometimes it gets bad enough that itll stall on its own and the only way to keep it running is rev it to 4000+ rpm and it scares the children- think about the children! Also you get nasty glares from the elderly too

[EDIT]- also soccer moms give me dirty looks

#2

First off - screw the soccer moms, elderly and especially the kids!

Seriously though, mine does the same thing and IIRC I have heard it described (from L28E folks) as a form of vapor lock.

Because the fuel rail is mounted above the engine and is subject to heat soak (especially after you turn off the engine after dirving for a while) the fuel gets hot, possibly close to boiling, and when you restart, the less-dense fuel is not doing the job. When I was younger (realize that my 83 was my 1st car), I thought the same thing as you, that I have some sort of FI issue. In actuality, revving the motor brings up the denser, cooler fuel from the tank and the car runs fine.

I notice almost every time I drive the car when it is moderately warm outside and I try to restart soon after I have shut it off, sometimes it dies, sometimes it will idle rough, until it uses up the hot fuel in the rail.

When you leave the key in the on position for a while you are pressurizing the rail fully (I typically wait until I hear the pump shut off with the key in the on position to start the car) and that is having some effect on the running condition.

So basically, it it just a caveat of these engines - nothing really to worry about - or so I am told.

#3

Gasser fuel injectors leak when they become worn. Other than your description of the non-occurance of the problem if you leave the key on/engine off for a minute, what you describe is typical of leaking injectors: flooding.

The fuel rail is supposed to remain pressurized for hours after the engine is shut off, precisely to eliminate vapourisation of the fuel in the plumbing.

"Vapour lock" is something completely different. On vehicles where the fuel pump is mounted on the engine, enough heat at the fuel pump (transmitted through the fuel pump's body and exhaust plumbing) occurs that the suction stroke of the pump reduces the pressure on the heated fuel enough that a state change occurs -- the liquid gasoline being "sucked" momentarily changes to a gas, and the increased volume of the gas means that the pump's diaphragm won't move anything. Pressure falls off at the pump's discharge, and the engine stalls.

Vapour lock doesn't occur in FI vehicles, because there is no "suction" at the hot areas of the car -- the pump is remotely located, usually at the fuel tank but sometimes along the frame rail.

Kassim, because you can change the symptom by leaving the key on/engine off, I think your focus on the thermo-time switch is a good idea.

#4

I would tend to disagree Al. This problem is very common across all L-series gasoline engines. A search on ZCAR, ZDriver, HyridZ, would show many experiences similar to what kassim and I have experienced.

I for one have all new sensors and injectors on my L24E and am 100% confident that they are all functioning correctly, yet I still experience the issue on warm days, just like I did before with old injectors and sensors.

Let us know if you are able to eliminate the issue. I have lived with it as long as I have owned this car through 3 sets of injectors, 2 thermotime switches, 2 different ECUs (MT and AT), 2 CHTs, etc.

#5

Want to borrow a Snap-On fuel pressure tester apparatus? That will let you check residual system pressure, to insure that the system is remaining pressurised after engine shutdown (both the regulator and the FP check valve are leak points), and to ascertain pressure rise at the rail when you turn on the key. If the pressure rises slowly, look at the fuel pump or fuel restriction (inline filter, tank filter).

Leaky injector(s) is the most common problem though. Back in the day, I used to use "rebuilt" injectors and could rarely get a year out of them before they began leaking again. Also back in the day, the old L-Jetronic days of 1968 VW and '73 Volvo, I had a permanent fuel pressure gauge installed to monitor the rail pressure. Those early Bosch L systems were a real bastard.

#6

Fuel pressure might be something to think about. The FPR is also new on my L24E and I have recently re-installed the rail, so I know all of the clamps are tight, but the issue is always there. Drive for a while. Stop for a while. Start it back up - rough, rough, rev, rev, rev - all fine. Always seemed like a non-event to me.

I know that a lot of my Porsche 914 friends mount FP gauges on their rails to monitor the pressure. We have D-Jet on our 2.0s.

#7

I may have leaky injectors, my injectors are 23 years old and hasnt been cleaned to date, mabye ill clean the injectors and see if my problem changes.

I do remember that the problem got worse after i put a bottle of fuel injector cleaner in the gas tank. Either it removed a little bit of dirt and it opened up a passage for it to leak or it eroded a seal and I have to get new injectors. (hope its just dirt)

#8

Installed the pressure gauge- I think i have either a pump or regulator problem. It reads 30-37 psi when cold (normal) and slowly lowers itself down to 17-15 psi when hot. Tommorow ill try pinching off the return hose and see if the pressure shoots up a little (regulator problem) or if it dosent (pump problem).

Whatever the problem is it grew from just a little slow starting when warm to a little stalling problem, and today my car couldnt start when it was hot leaving me stranded in the bank's parking lot for an hour while trying to cash Al's check (got your MO today- gotta ship tommorow, the bank closed before i got a chance to open your letter).

The problem is not a air intake/vaccum problem its defnitley a fuel system problem because pushing on the MAF's flap makes the engine run better and a little bit of starting fluid makes the car run pristine again.
Also the car wont pass 2700 rpm and accleration is about the equivilant of a kid on a bike (I cant keep up with school busses picking up children).

#9

Ben, what is the ambient temperature of where you drive your maxi? Also do you use the air conditioner?

#10

kassim503 wrote:Installed the pressure gauge- I think i have either a pump or regulator problem. It reads 30-37 psi when cold (normal) and slowly lowers itself down to 17-15 psi when hot.

Dumb question, but have you replaced the fuel filter?

This is pretty close to the usual clogged fuel filter symptom. And the pressure test point is downstream of the fuel filter too. What I'm getting at is the the fuel pump might be OK.

BTW . . . I (actually, Caxambu) salvaged the fuel pump from the '83 Gasser we dismantled three weeks ago. They make great fuel transfer pumps -- I bought one at a JY in 1996 and used it for a transfer pump for a long time, but don't have it anymore and thought I'd use this one for that, but if you decide you need a new (used) FP and can't find one, I could ship you this one for cheap. I almost pulled the one off the '84 at the Lakewood JY but figured when would I ever need two of them?

But if you haven't already, replace the fuel filter first for low pressure problems.

#11

kassim503 wrote:Ben, what is the ambient temperature of where you drive your maxi? Also do you use the air conditioner?

Ambient temperature varies. The issue is most noticeable in the summer when it can be anywhere from 75-80 on a cooler day, to 95-100 on a hot day. Rarely gets above 100. Humididty is usually around 30% (maybe less) and obviously decreases as the day goes on, maybe 10% in the late afternoon.

I have never really used the AC, just because it makes the car such a dog from a stop when it is on. Right now I have the belt off, so I can't use it.

#12

Today the car left me stranded

fortunatley it was 3 houses down from mine so I was just able to push it back. I popped the hood and got the car to start, found the car was leaning out.

Took off the fuel filter and blew thru it, gave a little resistance so I bought a new one. Problem wouldnt go away, disconnected vaccuum line on regulator, pressure didnt rise. Plugged the return line, pressure still low.

Finally I was able to get a new fuel pump from NAPA ($145 total) pulled the old one, ready to put the new one in, I forgot to buy hoses while i was there so im just going to give up for today and enjoy the weather.

Talking about fuel pumps for fuel transfer pumps I use a pump from a mitsubishi galant that I parted out, its got a 12-120 volt adapter wired up to it, its great for kerosene (heaters)

#13

Fuel pump was the culprit

Also the car dosent run bad when it starts warm

#14

I'm bumping this thread because I think I have a glorified version of this problem that seems to have gotten worse as of late.

When I drive the car for long periods (read: up to operating temp for several minutes) shut it off, then try to restart it a short time later (while it is still warm) it starts and dies - immediately. This does not happen if allowed to cool down. I have to hold the pedal down and it will chug, chug, chug and eventually it will rev up. I need to rev it pretty hard - 4-5K to keep it running, or very quickly get it in gear and go. Under load the issue will go away. It feels like once the fuel is used or something eliminated in the lines (air?), it is fine. Runs perfectly.

Feels like it is loading up with fuel maybe? Bad cold start or thermotime perhaps?

Unlike Kassim's issue, it will not go away if I keep the key in the on position for a short while before trying to start it. The thermotime and water sensors are relatively new, but I haven't checked them as being OK yet.

I thought I'd probe here for some suggestions while I check the sensors' reistance and see what I have.

TIA.

#15

Show us more pictures of your grille badge!

From what I see I like it

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Rough running when hot

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