84 VW Rabbit GTI - Hard to start when hot

Discussion:

(too old to reply)

2006-08-30 22:55:19 UTC

Regarding my recently aquired 84 VW Rabbit GTI - manual trans - 8
valve.

I have read posts regarding topics relating to hard, hot starts but
have some additional questions.

The car starts fine when it's completely cold, but takes quite a lot of
cranking in order to get it to start when the engine is hot. I checked
the cold start injector and found that it is working as it should on a
cold start (sprays for about 8 seconds, then stops). However, the cold
start injector does not operate at all on a hot start. The car does a
"hot start" when I manually put 12 volts to the cold start injector for
a few seconds while a helper starts the car.

The other posts suggest that the failure is in the "hot start relay".
I can not find a hot start relay on the car, or referenced as a part
for this car. The only thing close is the CIS/Lambda relay. Is that
it?

I am about ready to add 12 volts directly to the cold start injector
via a switch or, timer relay.

Any suggestions?

Thank you in advance!

Jeff

SFC

2006-09-01 10:32:14 UTC

Permalink

Again a typical case of vapour lock. Fuel pressure drops off too quickly.
The fuel system should hold the pressure (about 14psi) for at least
20..30min. Check for leaks and if it's a cis injection replace the o-rings
of the fuel pressure regulator located in the fuel distributor.

SFC

Post by JH
Regarding my recently aquired 84 VW Rabbit GTI - manual trans - 8
valve.
I have read posts regarding topics relating to hard, hot starts but
have some additional questions.
The car starts fine when it's completely cold, but takes quite a lot of
cranking in order to get it to start when the engine is hot. I checked
the cold start injector and found that it is working as it should on a
cold start (sprays for about 8 seconds, then stops). However, the cold
start injector does not operate at all on a hot start. The car does a
"hot start" when I manually put 12 volts to the cold start injector for
a few seconds while a helper starts the car.
The other posts suggest that the failure is in the "hot start relay".
I can not find a hot start relay on the car, or referenced as a part
for this car. The only thing close is the CIS/Lambda relay. Is that
it?
I am about ready to add 12 volts directly to the cold start injector
via a switch or, timer relay.
Any suggestions?
Thank you in advance!
Jeff

Erik Dillenkofer

2006-09-02 09:20:38 UTC

Permalink

Replace the fuel accumulator (near the fuel pump by the tank). The
accumulator holds pressure in the system and prevents vapor lock.

Post by SFC
Again a typical case of vapour lock. Fuel pressure drops off too quickly.
The fuel system should hold the pressure (about 14psi) for at least
20..30min. Check for leaks and if it's a cis injection replace the o-rings
of the fuel pressure regulator located in the fuel distributor.
SFC

One out of many Daves

2006-09-02 14:38:13 UTC

Permalink

TEST TEST TEST
It is best to purchase some tools to monitor fuel pressure
Before just throwing parts at your problem, unless price is no object. ;-)

So many items could cause your problem and it could cost you over $600 just
in parts with injectors, fuel distributor, fuel pump or it's check valve or
relay, fuel accumulator, plus whatever else I have forgotten about like
slightly leaking fuel lines.
I had to do this with a Scirocco saved from the junkyard and it needed
almost everything. Started up instantly at all times though.
--
JMHO
later,
dave
(One out of many daves)

Post by Erik Dillenkofer
Replace the fuel accumulator (near the fuel pump by the tank). The
accumulator holds pressure in the system and prevents vapor lock.

Post by SFC
Again a typical case of vapour lock. Fuel pressure drops off too quickly.
The fuel system should hold the pressure (about 14psi) for at least
20..30min. Check for leaks and if it's a cis injection replace the
o-rings of the fuel pressure regulator located in the fuel distributor.
SFC

Dustin

2021-10-02 04:45:02 UTC

Permalink

What does this part look like

--
For full context, visit https://www.motorsforum.com/vw/84-vw-rabbit-gti-hard-to-start-when-hot-34684-.htm

Jim Behning

2006-09-09 01:57:36 UTC

Permalink

I think a different control pressure regulator fixed the problem in my
84 GTI. Test pressure guage was not reading correctly.

r***@peoplepc.com

2006-09-11 03:02:27 UTC

Permalink

The post alluding to vapor lock is probably correct. The CIS system is
very sensitive to having sufficient residual pressure in the system
when the vehicle is hot. Often the cuprit is the check valve at the
fuel pump. If the smallest speck of rust gets caught in the check
valve it will not close, and the fuel will return to the tank, ergo a
loss of pressure. Often this can be heard, when the engine is turned
off, it sounds like a series of pings coming from the area of the gas
tank outet. It sometimes is immediate and other times very slow
depending on the size of the speck of rust or debris.
One can check this by loosening one of the bolts that seure the
banjo fittings to the fuel filter --- if the check valve is faulty,
there will not be a sudden release of pressure. if the check valve is
ok you will get a spray of gas. One should be careful in doing this as
one can get a facefull of pressurised gas if the check valve is ok.
On my 81,82, and 83 rabbits there is a hot start pulse relay that
is not integrated into the fuse panel --- it is in its own separate
holder, usually affixed to the fuse box by tape or a tie fastener -- i
have also seen them merely stuffed behind the box or dangling loose.
Since i do not have a 84, i'm not sure where its located, but when
functioning property, it causes fuel to be injected on an intermittant
basis in very short squirts during the initial cranking. Its called a
hot start pulse relay and Bentley shows its location on page 49 of
section 4, above the fuse box and say it is identified by its three
terminals and part no 813 906 064. Every post 1980 rabbit has the
relay.

Jim Behning

2006-09-12 00:49:12 UTC

Permalink

Bad cpr will cause a loss of residual pressure.

Post by r***@peoplepc.com
The post alluding to vapor lock is probably correct. The CIS system is
very sensitive to having sufficient residual pressure in the system
when the vehicle is hot. Often the cuprit is the check valve at the
fuel pump. If the smallest speck of rust gets caught in the check
valve it will not close, and the fuel will return to the tank, ergo a
loss of pressure. Often this can be heard, when the engine is turned
off, it sounds like a series of pings coming from the area of the gas
tank outet. It sometimes is immediate and other times very slow
depending on the size of the speck of rust or debris.
One can check this by loosening one of the bolts that seure the
banjo fittings to the fuel filter --- if the check valve is faulty,
there will not be a sudden release of pressure. if the check valve is
ok you will get a spray of gas. One should be careful in doing this as
one can get a facefull of pressurised gas if the check valve is ok.
On my 81,82, and 83 rabbits there is a hot start pulse relay that
is not integrated into the fuse panel --- it is in its own separate
holder, usually affixed to the fuse box by tape or a tie fastener -- i
have also seen them merely stuffed behind the box or dangling loose.
Since i do not have a 84, i'm not sure where its located, but when
functioning property, it causes fuel to be injected on an intermittant
basis in very short squirts during the initial cranking. Its called a
hot start pulse relay and Bentley shows its location on page 49 of
section 4, above the fuse box and say it is identified by its three
terminals and part no 813 906 064. Every post 1980 rabbit has the
relay.