Problem starting when hot

fogcity · 08-25-2003, 08:53 PM

I know it's been talked about a lot before, but was there any common solution to check and fix when the car doesn't start right off when hot?

My symptoms (which are rare) is that I'll drive on a hot day, park for about 10min to an hour, and then it doesn't want to start very quickly. Normally it starts right up but today I had to crank it (without stopping) for about 5-15 sec. It did always start on the first (long) try, but sort of "stumbled" to life instead of roared.

Thanks for the input. I'm back off to the knowledge vault.

fogcity · 08-25-2003, 09:16 PM

Okay, from doing the search I can't figure out what all that fuel pressure readings/testings are, but I can check to see if my fuel relay is sitting right. Except, of course, someone has to tell me where to find my fuel pump and mentioned relay? Also, all the info I searched was for pre-1984 cars. Didn't something change regarding fuel delivery then?

GrindingGears · 05:47 PM

My SC does the same thing. In the mornings it fires right up, like my mom's Lexus. In the afternoon when it's hot it starts up like my brother's 1970 Chevelle. Doesn't bother me, but I'm curious why?

Wil Ferch · 08-26-2003, 08:23 AM

I really wish there were some concrete suggestions for the 84-89 cars on this point. My 85 does this too for hot re-starts. The SC's have a host of other possibilities as to what the problem is ( example: check valve at the fuel pump defective).

Some of these SC concerns translate over to the 3.2 Carrera's but it would be nice to know specific 3.2 issues, too.

---Wil Ferch

bigchillcar · bigchillcar's Garage

Will,
My '74 has a check valve in the fuel pump, but I don't think an '84 pump does. I think I'd suspect a faulty accumulator.
Ryan

ChrisBennet · ChrisBennet's Garage

Carreras have a check valve as part of the pump. They don't have an accumulator. The sensors on these cars can behave differently when they are hot. I would try tricking the illiminating the head temp sensor by replacing the it with a resistor (in the connector) of the right resistance. I'd also measure the resistance of the head temp sensor. This isn't likely the problem but the test is easy and cheap.
-Chris

BGCarrera32 · 08-26-2003, 09:56 AM

Quote:

I really wish there were some concrete suggestions for the 84-89 cars on this point.

Me too. So I finally took mine in to the shop. The check valve on the fuel pump only keeps fuel from flowing back through the pump on the pressure line, and mine is new. My problem as it turns out is the fuel pressure regulator, which is on the return line of the system. It is located on the drivers side behind the injector rail, and connects right to the hose headed back to the tank. The shop said my car would not maintain adequate fuel pressure after shutdown, and just because the regulator held vacuum with a hand pump, doesn't necessarily mean its any good. Since the Carrera pump doesn't run or "prime" the system when the ignition is turned to "on", it relies on the power of the pump alone to pressurize the system. So, if a regulator isn't holding the correct pressure at startup (allowing the pump to immediately build pressure), the injectors could be fuel starved for several seconds while the engine cranks. I had an engineer friend tell me it takes like 200% more fuel to start a cold engine, and 600% to start a hot one...(I think I have that right).

I went throught the CHT checks and resistor swap as well to no success. The next time your car acts up, jump the fuel pump fuse and run it for 15 seconds, then jump back in and try to start the car. My bet is that it will fire right up...

-BG

john70t · 08-26-2003, 10:09 AM

Although a stumbling firing sounds like lack of fuel, I don't think it's the fuel pressure if there is only a problem with the hot start.
Wouldn't the engine need more fuel on cold start and have more time to bleed off pressure sitting overnight?

BGCarrera32 · 08-26-2003, 11:09 AM

Quote:

I don't think it's the fuel pressure if there is only a problem with the hot start.

Then what do you think it is?

Wil Ferch · 08-26-2003, 12:47 PM

BGCarrera32:
Thanks for the data...and I personally think you're on the right track. Sure, it *may* be the internal check valve on the fuel pump, and adding a SC type check valve may help. It also could be injectors that bleed-down pressure and don't hold. If it's the fuel pressure regulator , as you suggest...on the driver's side...it just as well can be the similar looking fuel pressure damper on the passenger side of the car, too.

So...it can be any one of these 4-5 things ( maybe even the fuel pump itself)....so it would be nice to know the "common" failure point as we go digging into trouble-shooting analyses. Thanks BGcarrera32!
---Wil

BGCarrera32 · 08-26-2003, 01:17 PM

No problemo Wil-

thanks for all your past suspension advice. Here's my further reasoning that its the fuel pressure regulator- besides what my shop says (I have the *exact* same problem as user fogcity)

I have replaced my-

injectors
fuel pump and check valve (located right off the pump on a Carrera)
intake gaskets
throttle body sealing o-ring
all vacuum lines
all vacuum line rubber fittings to the regulators
intake boots
CHT
speed and ref sensors
cleaned all connections at injectors and 4 pronger at bulkhead
cap rotor plugs valve adjust fuel filter yadada

None of these things has resolved the issue.

Quote:

it just as well can be the similar looking fuel pressure damper on the passenger side of the car, too.

But, the fuel pressure regulator is the only one of these two that would allow fuel pressure to bleed off back to the tank...and assuming you aren't smelling fuel...

Good luck-
BG

ChrisBennet · ChrisBennet's Garage

I wonder if any of the fuel return hose is flexible enough to pinch off in order to keep the pressure up?
-Chris

BGCarrera32 · 08-26-2003, 05:13 PM

I've also heard you can crush the regulator can in a bench vise slightly to up the pressure (risky? nahhhh)...maybe this line (fuel regulator is above it).

You'll also notice my engine-out highly specialized fuel line condom in green...

fogcity · 08-26-2003, 06:59 PM

"The next time your car acts up, jump the fuel pump fuse and run it for 15 seconds, then jump back in and try to start the car. My bet is that it will fire right up... "

BG - Can you explain how to do this? "Jump" the fuel pumb fuse? "Run it" for 15 seconds - run what?

You've given me a lot of help and good ideas (whether you knew it or not) in the past: I'm glad we share the same year car.

fogcity · 08-27-2003, 08:00 PM

BG? Anyone?

ChrisBennet · ChrisBennet's Garage

BG,
On my '86, the fuel pump fuse is something like #7 if you go by the #'s on the fuse box lid. #1 is the fuse closest to the "skinny end" of the fuse box i.e. closest to the driver/rear of car. Look at the fuse box "card" on the outside of your fuse box cover.
I run a jumper between the bottom of #7 and #6 to force the fuel pump to run. If you don't have a jumper you can just bridge the bottom part of the two fuses with something metal for a few seconds. You should hear the pump run when you do this.
-Chris

BGCarrera32 · 08-28-2003, 11:52 AM

Sorry, just saw the thread again...

I swear mine is labeled from the front bumper end as #1 headed back towards the driver as #22 or however many there are...

Anyway, the idea is to jump power to the fuel pump. Counting from the front bumper end on mine, connect a jumper wire to fuse 16 (I think 16 is the pump) and touch the jumper to fuse 17 in the panel (horn or something). The fuel pump should run. What I *highly* recommend you do is get a cheapo fuse holder in line on your jumper wire and use the same value fuse as the fuel pump so you don't fry anything inadvertantly.

Anyway, you get the idea...

-BG

ChrisBennet · ChrisBennet's Garage

Quote:

Originally posted by BGCarrera32
What I *highly* recommend you do is get a cheapo fuse holder in line on your jumper wire and use the same value fuse as the fuel pump so you don't fry anything inadvertantly.

Wow, and I thought I was being careful because I didn't suggest bridging the fuses with your tongue...

-Chris

BGCarrera32 · 08-28-2003, 12:01 PM

Quote:

Wow, and I thought I was being careful because I didn't suggest bridging the fuses with your tongue...

But if you have a tongue piercing, its probably o.k.. And I don't BTW...

If I recall this is what I did, black blob is inline fuse.
And now that I look at it, sure is *brilliant* having all that electrical right by the fuel feed and vapor lines...

1fastredsc · 08-28-2003, 12:02 PM

My 44 used to have a hot start problem and it was the fuel check valve. All it does is hold fuel pressure in the system after you shut the engine off. Of course it would start just took a lot of cranking, but after replacing the check valve, it would immediately fire up.