As I move through my '90 U.S. spec Majestic 4.0 correcting issues and performing maintenance I do have a question about hot start.

Cold start is fine, the engine jumps to life immediately upon a turn of the key. Hot start is different, however.
The engine will crank and "quietly ignite" (for lack of better words).
It is certainly not like the robust, bang on cold start.

I just turned 81,000 miles and bought the car with 78,339 on it this past January.

This has been an issue since I bought the car and the car always starts.
Now, the time has come for the fix.
I am inclined to think the issue may be either a vacuum or fuel pump/fuel system deficiency.


I initially thought my problem might be the non-return valve P/N JLM1854, but I would expect difficult starting even on cold start.
My problem could be the fuel pump itself when it gets hot...?



Any ideas?
As always, my sincere "Thank you" for any ideas.

Roger

 

Hi Roger,

One possibility is that the Coolant Temperature Sensor (CTS) is out-of-range or its electrical harness is corroded, loose or damaged. The Engine Control Module relies on the CTS signal to apply cold-start fuel enrichment. If the CTS signal never reaches the proper value to tell the ECM to terminate cold-start enrichment and go into closed-loop fueling, when you start the engine hot the fuel mixture will be over-rich, slightly choking the engine. The CTS is the two-wire sensor mounted on top of the coolant thermostat housing at the left front end of the engine. The single-wire sensor provides the signal to the instrument cluster temperature gauge.

Another possibility is that the Fuel Pressure Regulator (FPR) is no longer holding as much pressure in the fuel rail as it should, and when you shut off the hot engine, the sudden loss of pressure is allowing the fuel in the rail to partially vaporize, leading to "partial vapor lock," if there is such a thing. The FPR works in conjunction with the non-return valve to maintain +/- 40 psi in the fuel rail, but with age both components tend to fail partially or completely.

Replacing the FPR is not difficult, and the part is affordable (search eBay for the most affordable options). The photo album at the link below shows how I replaced the one on our '93:

Welcome to Jag-lovers - Members Photo Viewing Page


The non-return valve may also be contributing to the issue, since it's the other component responsible for maintaining fuel pressure. I can't recall on a '90 if the valve is at the inlet of the fuel filter or in the plastic fuel pump canister inside the fuel tank. If it's in the fuel line ahead of the fuel filter, it's an easy swap. If it's in the tank, it's easiest to just add a new check valve in the fuel line between the fuel pump and fuel rail. Below is a link to a photo album showing how I did this on our '93:

Welcome to Jag-lovers - Members Photo Viewing Page


I'll look forward to hearing suggestions from other members.

Cheers,

Don

 

Roger:
It's been a while since I've seen anybody talk about the "key cycling trick", so I guess it's about time! If you cycle the key through positions I and II (without cranking) a few times to re-pressurize the line with a couple of priming bursts, will the car start pretty much as normal? If so, as Don suggested, I'd be inclined to look at a leaky check valve. I had the same set of symptoms on a '94 I used to own, and installing the additional check valve did the trick.

Cheers,
Scott

 

Thanks fellas, gives me a starting point for this week.

 

My problem was the coolant temperature sensor.
I installed a new CTS (P/N WT5044 5 minute job) took it to the market and that hot restart was robust.
Just what I was looking for.

 

Sweet! Well done and thanks for reporting back!
Scott

 

You're welcome for the "thank You". These are great cars and we have to pass info like mine along to help each other in keeping these cars on the road.

 

Thanks for letting us know, Roger! Hopefully it was that simple.

Cheers,

Don

 

To revisit this old thread my problem was not the CTS. I'm zeroing in on the fuel pump check valve P/N JLM1854. My research has found a/the matching Bosch P/N 1-587-010-539. It's modest cost encourages me to try one. To be sure, I'll report back to the forum on my results.