hksamc

Hi all,
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The car has a very nice idle, good cold start, smooth run.

The issue happened when it was cruising under 2k rpm at fifth gear, sudden no throttle for 2 seconds...after 2 seconds throttle came back n it ran normally. The second occasion was at the traffic night, another under 2k rpm scenario, suddenly no throttle for a second, then acceleration came back n it ran normally. The last occasion was at the parking lot, reverse gear n parking, can feel that the car was running rich...

3 occasions happened on the same day...It was a very hot weather with direct sunlight, at least 104F or 40c, humid and hot. Was stuck in traffic jam in 10 min before the above scenario, stop and go using first gear and clutch.

​Any idea? thanks a lot.

Car cooled down for a night, this morning no such issue when moving in the parking lot.

Checked vacuum, no vacuum leak.

hksamc

I am suspecting vapor lock in fuel rail because of heat...any idea? thanks

theiceman

id lean more to coil or something else electrical if it were me.... no reason why i just tend to find it more likely .. maybe even a HTS going bad.

ab1752

I'm going through the same issues with my 89. I'm thinking this will be flywheel sensors so my parts cannon is loaded as such and will swap these out in August. Yay!

old man neri

Next time it happens take a look at your tach. Does it indicate correctly or does it go to zero? This should give you direction.

ab1752

Not to highjack the OPs thread but my tach stays "alive" and follows engine speed correctly.

hksamc

my tach stays alive at 1500rpm, didnt drop to zero too.

darylbowden

I had this happen with my '86 last year as well. It just felt like it really stuttered under load, especially uphill for a few seconds. It would then recover and then do it again later.

I meant to have my mechanic take a look at it, but then it just stopped. My guess is the vapor lock type scenario as it only started when I was on a super long road trip last summer (SF to LA) and then continued a bit through the teeth of the summer heat. I haven't noticed it at all this year and this car is one of 3 in my DD rotation so it gets a lot of use in this heat.

old man neri

It's been a while but I believe that indicates that it is not a crank or position sensor, or the computer having a fit. Maybe ignition related? Have the car running and jiggle the coil and key? I'm sorry I can't be of much more help.

hksamc

Thanks for your reply.
I have the same feeling that it relates to vapor lock scenario. Maybe a minor vapor lock issue. I seldom drive the car during excessive heat but i did it in the last occasion since i was fixing the oil leak at my mechanic's shop. I was stuck in traffic jam unfortunately and that scenario happened.
But the question is whether DME L jetronic vehicles are subject to vapor lock? I understand that the engine is at the back and the cooling is known to be old fashioned.

I drove the car inside the parking lot and it was perfectly good.

One additional info is that the car had 1/4 tank of gas.

Cheers.

hksamc

No actually. The car was actually running well. Just like you floor the gas pedal but nothing happened. the engine did not rev and stay at the rpm that it used to be....say 1800 rpm, floor the gas pedal, still 1800rpm, no jiggle...i was thinking the throttle wire was broken but it isnt. after 2 secs later, it came back to normal again.

ab1752

Cylinder head temp sensor is faulty in my car. Also did the flywheel sensors too, in spec but it's not a fun job so knocked all 3 off at once. Good luck, Op, please circle back with your fix!

hksamc

Got some updates.

Changed the cylinder head temp sensor. No luck.

However, the symptoms were getting obvious. It only happens during hot start. Lasts for 5 mins or so. The car was running rich.

I am now shifting the focus to the fuel pressure regulator and the fuel damper. I have done some research that the fuel will go into the vacuum tube to the intake manifold if the diaphragm inside the regulator is broken.

I am going to change both fuel pressure regulator and damper this weekend.

Cheers.