TL;DR: Chronic hot/warm restart (30–60 min heat-soak) traced to residual pressure bleeding off. Confirmed with a pressure test. Isolated the leak to the primary pressure regulator (not the check valve or frequency valve). Replaced the regulator internals—problem vastly improved.
Symptoms
I initially replaced:
Neither changed the warm-start behavior.
Lesson: With K-Jet, buy/borrow a proper pressure test kit first and diagnose. Otherwise you’ll waste money and time.
The Key Measurement
With a CTA fuel pressure test kit installed:
Working theory: Pressure bled off quickly → hot fuel boiled → pumps had to fight vapor before injectors got liquid fuel → long cranks.
Where can pressure go?
Residual pressure is primarily retained by:
…plus the accumulator helping to hold pressure steady.
So a fast drop usually means:
Mistake #2 — Not isolating before replacing
Because it was easier than opening the fuel distributor, I replaced the secondary pump and check valve first. No change—pressure still dumped.
Lesson: Isolate the failure point before buying parts, even if it’s more awkward.
How I Isolated the Leak (simple plugs + caution)
Safety first: Fuel, pressure, and spark are a spicy combo. Work cold, ventilated, fire extinguisher handy, no smoking, eye protection, and keep runtime short when you’re intentionally blocking return lines.
This was conclusive: the pressure regulator wasn’t sealing/holding residual pressure.
The Fix
I was hesitant to open the pressure regulator at first, but a local CIS-savvy friend sourced a pressure regulator rebuild kit (o-rings/shims/spring/regulator unit equivalent linked below). We:
After the PR refresh: Residual pressure held. That also implies the frequency valve was fine.
Results Now
Tools, Parts & References
Test/Hardware
Part I ultimately needed
Takeaways (so you don’t repeat my mistakes)
Happy to answer questions or share additional photos of the test setup/plug locations if helpful.
Special thanks: both Matt West (of west-cam) and GreyGooseRestorations were generous with their time and gave suggestions and helped me double check AI suggestions as I was learning. I really appreciate people who work hard to keep our cars running well, and many of these folks are very generous and helpful.
Symptoms
- 1987 Esprit Turbo HCi (US) with Bosch K-Jetronic.
- For both me and the prior owner, warm starts after ~30–60 minutes often required 20–40 seconds of cranking. Sometimes a little throttle seemed to help, but hard to be sure.
- Only once in two years did it fail to start, and that time the battery was low—likely a second issue overlaying the main one.
- Practical effect: post-meal restarts = anxiety.
- Car owned ~2.5 years.
- Prior owner installed a rebuilt fuel distributor from SpecialTAuto.com (DeloreanAutoParts.com).
- Two different Lotus pros had a go at it; one admitted limited K-Jet familiarity. Given what I know now, it's clear that this is a pretty standard k-jet issue and it's clear neither knew how to address k-jet fuel systems.
- After moving the car to Maui (no local Lotus specialists I know), I decided to learn K-Jet and do it myself. I got to work by ordering a recommended book (link below) and watching a lot of youtube videos on k-jet maintenance. Once I understood the basics, I started chatting with AI.
Mistake #1 — Replacing parts before testing
I initially replaced:
- Warm-Up Regulator (WUR) with a rebuilt unit (k-jet.biz).
- Fuel accumulator (upon inspection I noticed mine was leaking).
Neither changed the warm-start behavior.
Lesson: With K-Jet, buy/borrow a proper pressure test kit first and diagnose. Otherwise you’ll waste money and time.
The Key Measurement
With a CTA fuel pressure test kit installed:
- After shutting off the pumps, system pressure fell to zero within 15–20 seconds.
- It should hold residual pressure long enough to prevent vapor formation (vapor lock) during hot soak. Mine didn’t.
Working theory: Pressure bled off quickly → hot fuel boiled → pumps had to fight vapor before injectors got liquid fuel → long cranks.
Where can pressure go?
Residual pressure is primarily retained by:
- Upstream check valve (at the secondary fuel pump on this car), and
- Downstream pressure regulator (in the fuel distributor, returning to tank),
…plus the accumulator helping to hold pressure steady.
So a fast drop usually means:
- Bad check valve, or
- Leaky pressure regulator, or
- Leak between them (e.g., injectors dripping, line/fitting leak, or frequency valve stuck open).
Mistake #2 — Not isolating before replacing
Because it was easier than opening the fuel distributor, I replaced the secondary pump and check valve first. No change—pressure still dumped.
Lesson: Isolate the failure point before buying parts, even if it’s more awkward.
How I Isolated the Leak (simple plugs + caution)
Safety first: Fuel, pressure, and spark are a spicy combo. Work cold, ventilated, fire extinguisher handy, no smoking, eye protection, and keep runtime short when you’re intentionally blocking return lines.
- Block the return (briefly!):
- Removed the double banjo on the distributor return and the small bolt feeding the frequency valve.
- Plugged both ports on the distributor with DIN 908 drain plugs and copper washers (sizes below).
- Bumped the pumps ~1 second to build pressure, then shut off.
- Result: Pressure held → leak was downstream of metering, i.e., pressure regulator/frequency valve area, not the check valve or an upstream leak.
- Differentiate PR vs. Frequency Valve:
- Reconnected the tank return and the frequency valve outlet.
- Blocked only the frequency valve inlet with an M8 solid bolt (copper washers both sides).
- Safe to run pumps normally in this configuration (return is open).
- Result: Pressure still bled off quickly → pressure regulator (PR) was the culprit (FV not held open).
This was conclusive: the pressure regulator wasn’t sealing/holding residual pressure.
The Fix
I was hesitant to open the pressure regulator at first, but a local CIS-savvy friend sourced a pressure regulator rebuild kit (o-rings/shims/spring/regulator unit equivalent linked below). We:
- Pulled the old PR,
- Installed the new internals with correct o-rings,
- Re-tested.
After the PR refresh: Residual pressure held. That also implies the frequency valve was fine.
Results Now
- Warm/hot restarts after full heat soak + ~45 minutes: 2 seconds of cranking and it lights.
- Not quite “tap-key-and-catch” hot starts yet (which I do have on cold start), but night-and-day better than the 20–40 second cranks.
Tools, Parts & References
- Book: Bosch Fuel Injection & Engine Management — Amazon.com
- YouTube: Grey Goose Restorations — - Grey Goose -
Test/Hardware
- CTA fuel pressure test kit — Amazon.com: CTA Tools 3420 K Jetronics C.I.S. Fuel Injection Pressure Tester - Compatible with Bosch : Automotive
- CTA adapter set (to connect at WUR outlet on distributor) — 3422 - CIS Adapter SetDefault Title
- BelMetric DIN 908 drain plugs (I used M12x1.5 and M8x1) — Steel Allen Socket Metric Drain Plug, DIN 908, M8 - M30
- Copper washer assortment — https://www.amazon.com/dp/B0DJPB3821
- Simple fuel-pump jumper (two spades to one spade) to run pumps without cranking.
Part I ultimately needed
- Pressure regulator rebuild kit (fuel distributor): Primary Pressure Regulator
(A mechanic friend sourced a similar kit locally for ~US$200.)
Takeaways (so you don’t repeat my mistakes)
- Measure first. Get a K-Jet pressure kit and learn to use it.
- Prove where the pressure goes before buying parts. Simple block-tests can conclusively isolate the fault.
- Respect the system. Short, controlled pump runs when returns are blocked; use proper plugs and new copper washers.
- AI can help you learn, but verify details against your exact variant (Esprit HCi uses k-jet with lambda, not ke-jet, not original k-jet).
Happy to answer questions or share additional photos of the test setup/plug locations if helpful.
Special thanks: both Matt West (of west-cam) and GreyGooseRestorations were generous with their time and gave suggestions and helped me double check AI suggestions as I was learning. I really appreciate people who work hard to keep our cars running well, and many of these folks are very generous and helpful.
