View Full Version : Fuel Injection Help, please

06-01-2007, 06:02 PM
Looking for advice for my 280i. Familiarity with the Bosch Jetronic injection would be invaluable.

Current symptom: Runs very strong for a few miles, followed by short periods of engine cut-out. Not individual cylinders dropping, but total cutout. The engine didn't die, as I left the clutch/gear engaged and the engine eventually cleared and ran well again (for the entire return trip of 1 to 2 miles). Suspect fuel flow issue.

Recent issue: Wouldn't start (very unhandy at midnight as I was trying to impress the wife with the drive home from a party). Immediately suspected lack of fuel and diagnosed to dead fuel pump. Found a length of silicone gasket material sticking out of the pump intake snout - loosened by injector cleaner????

Anyway, replaced pump and added 40 micron screen filter in front of pump. Engine still wouldn't start, yet I now had fuel pressure. Boned up on Jetronic manuals and diagnosed to warm-up valve - regulator plunger stuck preventing no enrichment during startup. Figure that one out with no relation to dirty fuel, as the plunger is not on the fuel side of the circuit. Sitting too long?? Rebuilt warm-up reg and everything is fine - except for intermittent cutout.

Suspicions: The filters (replaced the very large post-pump Bosch canister filter) stops debris getting into the mechanical metering unit and injectors - but am I facing sediment buildup after the filter due to this 20 year vehicle that has only 12K miles on it??

I purchased an electrical fuel pressure gauge to monitor in the cab during the next event - hasn't arrived yet. Interested in ideas to work on getting reliability into this machine. Not looking forward to entire fuel system disassembly and cleaning - options?


06-02-2007, 06:48 PM
I was having all types of fuel problems so I thought. I unplugged the O2 sensor off the manifold and it ran like a champ. It takes 10 seconds. It might just work?

06-03-2007, 09:19 AM
Thanks, that is a very good idea. I am going to try it today. The lambda sensor shouldn't cause this to happen, but i guess when a "computer" is involved (this early Jetronic is pretty stupid - no microprocessor that I know of), anything is possible.

I am so tempted to drop a 4.0 in and do the Megasquirt injection route...

Your suggestion parallels this article in a DeLorean site, but the purpose of this article was to cure the idle hunt issue. You probably know we share the same injection system. Some of their tech bulletins elude to a common problem their owners have with improper long term storage - crap clogging the system. That's what is leading me down this path.

DeLorean article excerpt and link:

"For my daily driver car, I found I could get better overall performance (as well as eliminate the mixture oscillation) by unplugging the lambda
sensor and re-adjusting the mixture screw to it's sweet spot. The lambda circuit is primarily an emissions reduction system and has marginal value for engine performance."

tech article (https://www.dmcnews.com/Techsection/lambda_elim.htm)

P.S. I have heard from other sources that this can kill a good O2 sensor (if left in) - exposure to emissions without proper temperature of heater. But our sensor doesn't have a heater..... should be OK to leave in I'm thinking.

06-04-2007, 07:31 AM
Several years ago I had similiar issues and after going through the entire system with less than satisfactory results, went to an Offenhauser manifold and Holley carb. Reliability is no longer an issue!

06-04-2007, 10:21 AM
Thanks for the suggestion. I thought of that a while ago too, but decided to go stock. I am not as interested in that any more :+(

Any difference in power or throttle response??

06-05-2007, 08:51 AM
What is the part number of the Offy intake that fits, please? I have only found intakes for the US heads. Or did you change the heads??

06-06-2007, 06:49 AM
I'd have to dig through my records. It would be easier to call Tom at The British T Shop in Connecticut (former TVR dealer) who did the conversion and has all the parts ready to go for anybody who wants to do it for their 280i. He's very helpful 860-889-0178. JMH

06-06-2007, 04:33 PM
No need to dig up the records. I have a call into Tom - it seems he works by appointment only on Wednesday. Must be golf day.

I will report the findings to the forum. Thanks so much for the contact!

I picked up two used 4.0 complete engines today for $80. Figured I couldn't go wrong for the price. One overheated and the other has a rod starting to knock. At least they were both running when parted from the cars. Between the two I have a chance of upping the cubes and moving to a more modern injection system. Unfortunately it won't be cheap to rebuild, but over time, we'll see... Should be good for a lot more torque and a few more ponies.

Hopefully Tom's advice will keep me rolling thru the summer while I play with these new options.

06-06-2007, 05:13 PM
I guess I should consider myself fortunate that I have an excellent Bosch mechanic who keeps my injection running very smoothly and has no problem troubleshooting it if it's out of sorts.
Unfortunately, I know he's a rare commodity and there aren't a lot like him left out there any more.

06-07-2007, 10:27 PM
Oh my god - I talked to Tom. He is a walking museum of TVR's and other related trivia. What a nice guy! The knowledge this guy has boggles the mind.

No wonder I couldn't find an Offy intake for our import heads. Although Offy is no longer in business, apparently they still make parts (as recently as this April) - including the somewhat custom intake our cars use, for the good price of around $500. Add a Holly 390 for several hundred and a custom thermostat housing for $50 and viola - you are carbureted! I know it will cost more than $1K for my 4.0L project, but that's the route I will be going some time soon. Tom remembers a 4.0L project he set straight by removing the stock 4.0 injection that the owner never got working correctly following the swap and put yet another custom intake and Holley 390 on. It went like stink! With my new "Innovate" wideband Lambda logger and "Megasquirt" I'll get that stock 4.0 injection humming.

Other possible cutout causes that he had experience with; clogged charcoal vent canister (hundreds of dead spiders...) caused vacuum lock in the tank and the ignition control module (lots of issues with these). Fix for module; Napa part # MPETP40SB for $27.69 and in stock at my local NAPA! I am putting two under the hood so I have a handy backup... Hopefully this will lead me to the issue so I can enjoy the car this summer.

I received the "Prosport" electronic 100PSI fuel pressure gauge and will install that as an in-cabin trouble shooting tool. THIS LINE OF GAUGES IS CHEAP - $45 COMPAIRED TO OTHERS AT HUNDREDS OF DOLLARS - check them out:


06-08-2007, 01:11 PM
Glad you got ahold of Tom. I've known him since I moved here 19 years ago and can't say enough about him. JMH

06-08-2007, 01:15 PM
I would be sure to fit an isolater to the fuel line, as you do not want to fill the cabin with petrol.

06-08-2007, 01:26 PM
I'm with you on that isolator - I appreciate the reminder! But I don't need one.

What's so amazing about that Prosport link I have above is that it is an ELECTRONIC gauge - you would think at $45 it would be manual, but no.

I have it in-hand with the separate sender. The gauge has a plastic case, made in Taiwan, but it has a true stepper needle and will work very well for a trouble shooting tool. Their senders are available separately for those who don't mind using an ohm meter or a data logger like my Innovate :+). I believe the most expensive senders were around $14 (oil and fuel). The others (temp, boost) were much cheaper. Std 1/8 NPT fitting.

And Tom. What can I say. I can't remember talking to a nicer, more knowledgeable guy - oh, I lied, that would be Marshall! He even knew the dealer who swapped the VINs on those '87 280I's that were really '86 models (mine is one). I complained about them putting a small crack on the corner of my windshield and the shotty reseal job and he said it was not a surprise. It was done in a period of several days in an old boiler factory of all places....