Howell EFI, Timing, and Vacuum

[baileynb]

Hey guys, I'm running into issues and could use a little advice. 1972 Wagoneer, AMC 360, TH400. It does have an Edelbrock cam (can't remember the number) and an Edelbrock intake. No EGR. Howell TBI system with FlameThrower coil and distributor.

It's been running rough, I've been working out different things I've come across since buying it last year. I know I need to do a compression and probably leak down check. It was running "okay" with the carb it came with (also Edelbrock) but I put the Howell on with the FlameThrower distributor. The previous owner had an aftermarket ignition system that wasn't working correctly. I put the distributor in with engine at TDC on #1 cylinder compressions stroke and made sure the rotor was pointing so the fire order matched the diagram in the manual.

It took playing around with the timing to get it to run okay but recently started getting worse. I'm not sure what from the service manual to follow as far as setting everything initially. With the vacuum advance disconnected and plugged, the engine will idle around 700 warmed up and in park. I can set the timing to about 8 degrees BTDC and it idles okay. I plug the vacuum back on, go for a test drive, and it bogs down under load. If I put too much throttle (or go wide open) it sounds like it's backfiring through the exhaust. It also won't shift into third and struggles to even shift into second. I have to put about 12 degrees of advance without vacuum to get it to run better, but it still struggles with throttle under load. It will shift into third, but the shifts aren't smooth and consistant, but won't go over about 65 mph.

I put a vacuum gauge on it and with timing around 12 degrees (guessing since the cover only goes to 10) I'm only able to pull up to 14" of vacuum. If I advance any further on my timing, the engine struggles to idle. Setting timing at 8 degrees provides less than 10" of vacuum. It fluctuates beween 12 and 14". It's drivable, but I don't trust it long term. It still idles around 700 (it does occasionally surge between 650 and 750, but evens back out).

I've not done the IAC adjustment to set idle rpm, but not sure if it's necessary. I don't want to adjust timing out any further. Is there anything else I should check? I can't find any leaks, I've sprayed carb cleaner all around the throttle body plate and intake manifold. I have the front vacuum opening on the manifold is plugged, the rear opening on the manifold is being used for the heater controls (and also where I'm connecting for the vacuum gauge), the TH400 is using a separate dedicated manifold port, the large port on the throttle body goes to the PCV with a tee to the fuel vacuum canister, the port vacuum on the throttle body is capped with a bolt threaded into a short run of hose (Howell instructions say to use that for EGR), and the manifold vacuum on the throttle body is connected to the distributor. The port on the back is connected to the MAP. I installed Hydroboost when I installed disc brakes, so no brake booster (which was causing a vacuum leak).

The only other thing I can think of is to disconnect the fuel vacuum canister and put the gauge on the tee in case the canister is leaking. I'm going to also check fuel pressure, but I need to order a gauge, mine only goes up to 10 PSI. Any other advice or suggestion is greatly appreciated.

[tgreese]

Hi - did you buy the Howell system new from them, or used? I have found them quite responsive to technical questions via phone.

The ECU expects a tach signal. Normally it takes the trigger from the ignition coil on the factory ignition, the same as you would connect a tachometer to points ignition. What is the Flamethrower, points ignition or something else? Does it have a dedicated tach signal output? There is a signal conditioning board in the wiring harness close to the ECU that converts the tach signal to a pulse that is acceptable to the ECU. Pretty sure all it does is convert to a single 5V TTL-level pulse per coil trigger.

If you have the original Delco points ignition for '72, you could switch back to that and see if it clears up any problems with the Howell system.

Also the cam could be messing with vacuum at idle, and affecting the ECU. The MAP sensor looks at the manifold pressure, and vacuum fluctuates at idle with a hot cam, so I'm told. Howell could best comment on this.

I did not read through your theories - I think your problem is more basic than that. Suspect the Howell system would work properly when added to a good running engine without these performance modifications. The performance stuff may be ok - ask Howell about such things - but I'd suggest you need to start from a good running baseline before you add the TBI stuff.

I kinda think you made a mess of things when you put the Howell stuff on before you had the engine running the way you wanted it to. You also need to talk with Howell if your engine is modified. Now you've got the Howell conversion issues mixed in with the pre-existing engine problems. Maybe they aggravate each other or can be separated - don't know. Sorry to be negative here, but I think you need to face that possibility.

[baileynb]

Thanks Tim. FlameThrower is Pertronix electronic distributor with a stronger coil. The stock ignition was removed by a previous owner that installed a Comp Cams ignition system that was poorly wired in. I bypassed the bias resistor and ran the ignition switch wire to a relay I installed to provide full battery voltage to the coil (with 10 AWG wiring from battery). The Howell EFI kit was a new kit ordered directly from Howell. The coil (-) is connected to provide the tach signal.

I had previously reached out to Howell and was told the cam shouldn't be an issue with their prom. I've ordered an ALDL to USB cable so I can see the readings from the ECU. The only code I'm seeing from the SES indication is code 33, which from what I've read indicates low vacuum at idle (high MAP voltage).

I suspect it's not the stock cam only because there was paperwork for an Edelbrock cam with the mess of paperwork I received with the Jeep. Ironically, I got laid off and now have time to work on things, but not the money for parts... I didn't want to tear into too much and deal with purchasing new seals/gaskets and have another vehicle I need to get running. I was about to buy a 1975 Cherokee parts vehicle before getting laid off and had planned to rebuild that engine and swap the drivetrain to move to a manual transmission and repurpose the D20 to convert my International (with T18) to 4x4.

I probably just need to pull the timing cover to verify the timing marks are lined up properly and remove and reseal the intake manifold, maybe it's leaking from the lower side or somewhere I can't get a blast of carb cleaner into.

[tgreese]

Smoke machine? If I had a manifold leak that I could not detect otherwise, that's how I'd proceed. There are instructions online for building a smoke machine, or maybe you could borrow one.

There must be a way to check whether you have jumped time without pulling the engine apart. Dial indicator on the #1 intake valve? Timing chain slack should show up if you move the crank back and forth and watch the distributor rotor.

[Bakydnutbstr]

Sounds like timming chains shot ,too much slack slop in it. Do you know the engines mileage? Who knows what the PO did mechanically use the old chain set up or new, did he beat on the engine?
Spraying carb cleaner around manifold and carb when running ( worked for me ) causes it to run ruff er. Locating the air leak area.

[baileynb]

Yeah, no clue what the PO did. I think the PO I bought it from only had it for a few months and gave up after having an issue with the transmission (ended up being the kickdown solenoid) which is why I was able to get it so affordably.

No clue on the mileage, but doubt it's been rebuilt in the 50 years of existence.

[baileynb]

I did the compression check. Engine was warmed up and my wife had the throttle open as she cranked. Fuel pump fuse was removed and the coil wire disconnected.

1 - 110
2 - 130
3 - 120
4- 130
5 - 115
6 - 110
7 - 110
8 - 125

Can improper timing cause issues with compression, I don't think so, but I'm wrong a lot. The numbers seem low to me, but I'm not sure what the normal/acceptable range is on an AMC 360. Can a timing/compression issue cause low vacuum pressure? I ordered a cheap smoke machine (for the cost of stuff at the big box store, a $60 machine seemed about the right price) but don't have it yet. Still plan to do that before moving the Jeep to the driveway until I have funds to tear into and bringing the International in to finish fuel injecting it (Hamilton TBI system instead of Howell).

[baileynb]

Went back and did a wet compression check, forgot about it at first.

1 - 125 (+15 from dry)
2 - 130 (same)
3 - 140 (+20)
4 - 140 (+10)
5 - 140 (+25)
6 - 110 (same)
7 - 120 (+10)
8- 140 (+15)

So I think it's low across the board, but I have a mix of piston ring and valve issues? The ones that went up on wet tests are piston related and the ones that stayed the same are valve train? Even then, a few of them seem low even on wet, which would point to both a ring and valve issue?

Thanks.

[Bakydnutbstr]

The low compression can be caued by improper valve adjustment not opening enough or exghust staying open not seatingfully ,damaged valve - seat,worn shoulders on valve and seat,rockers need adjustment, weak valve spring. Rounded lobes on cam (runs like crap then), Piston rings worn , causes blow-by , head gasket bubbling in radiator or back into overflow tank, just somethings I’ve experianced .
You’re going about it the right way keep plugging away

[tgreese]

Compression numbers look fine. Valve timing can (does) affect compression, but I'm not sure if you can notice anything unless you had an earlier baseline to compare to.

I wonder if something got messed up when you switched to the new distributor?

You understand that the absolute firing order is all that matters? Ie the book order is 18436572 but #1 can be any location on the cap as long as the distributor rotor points to the #1 wire at #1 cylinder TDC. There is no required position for the #1 on the cap, as long as the wires are in order and the distributor rotor points to the #1 wire at #1 cylinder TDC. If you crank the engine with the #1 plug out, you can hear the compression stroke of #1 and align that with the timing marks for TDC. Then look at where your rotor points and make that #1, connecting the wires in order clockwise from above.

You can also get an idea about how much slack is in the timing chain by turning the engine with a wrench back and forth and looking at how far you need to turn before the rotor movement reverses. The distributor is driven off the front of the cam gear, and the chain slack is between the crank and the cam. You need quite a bit of slack before the chain will jump time.

Also, if this engine has never been apart, and has more than say 100K miles, the cam gear teeth could have broken. I believe the original cam gears for these engines had an aluminum hub with nylon teeth which come apart. Common for this era. This will definitely cause the engine to jump time. Maybe you can see the cam gear through the fuel pump hole? Maybe buy/borrow a bore scope and take a look in there? There are cheap ones that plug in to your phone.

Second thought - original cam gear seems unlikely if the cam has been replaced.

[baileynb]

I moved the Jeep out of the garage to bring in the IH for now.

I dropped the distributor in at no1 TDC on the compression stroke, I just aligned it in a way so the cap points matched the diagram and there was room to adjust without the vacuum canister hitting anything. I know my firing order is correct.

Once the IH is running, I'll bring the Jeep back in. I still need to smoke check the engine to see if there's a vacuum leak, I think that's my best first step.